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Why doesn't the ambient lighting condition change the perception of colors we see on a monitor?

Why doesn't the ambient lighting condition change the perception of colors we see on a monitor?


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Suppose that I take a picture of an object illuminated by an incandescent light bulb and I choose the daylight white balance setting. The picture I then get will display a white object as looking yellow, which is how the object would look had my brain not processed the image according to the ambient lighting conditions.

The question is then why the way the picture looks doesn't change depending on the ambient lighting conditions. If a white piece of paper continues to look white when illuminated by an incandescent light bulb, then why would that same piece of paper displayed on a computer monitor look yellow when I'm viewing it in a room illuminated by incandescent light bulbs?


The phenomenon you are referring to is color constancy: The apparent hue of a reflective surface remains constant even when changes in the spectral power distribution of the illuminant alter the wavelengths reflected from it (Mather, 2008). In other words, despite substantial changes in illumination, we usually experience the color of an object as being constant.

The spectrum of wavelengths that enter our eyes is jointly determined by 1) the spectrum of the illuminating source (a variable), and 2) The spectral reflectance properties of the object (a constant).

To achieve color constancy, an object's spectral reflectance is the constant color parameter that needs to be evaluated.

Any information that better characterizes an object's spectral reflectance is a cue to colour constancy. This includes (Mather, 2008):

  1. Local color contrast. Cone excitation levels of one surface relative to another remains constant when both surfaces experience the same change in illumination. Relative cone excitation levels are invariant ratios useful for achieving colour constancy.
  2. Color adaptation. Adaptation reduces the contribution from the source illumination by lowering activity in the most highly active cone classes.
  3. Global contrast. Global spectral changes generally represent changes in the illuminant; localised differences usually correspond to reflectance differences.
  4. Luminance highlights. Glossy surfaces offer near-perfect reflections of the illuminant, which can then be factored from the rest of the scene.
  5. Mutual reflections. The pattern of reflections that arise from different surfaces, under the same illumination, carries valuable information about the reflectance properties of each surface.
  6. Range of reflected spectrum. This gives an indication of the breadth of the illuminating spectrum.

A graphical example of the effect of lighting conditions is found below (Fig. 1.)


Bowl of fruit photographed under artificial daylight (left), hazy day light (middle) and clear blue skies (right. Source: Mather (2008)

The most powerful cue to constancy is thought to be local color contrast (Mather, 2008). In other words, the relative contribution of the different cone classes stays constant, despite differences in the spectrum of the illuminant.

In your example, the object (paper) is not represented by a reflectance, but as an image; a representation taken out of its context, and it will appear yellow. Even if the ambient lighting is the same, as in your example, the monitor displays a 'real' yellow color, which has a different spectrum, because it is not a reflectance, but it is generated by a light source: your monitor; as mentioned in the excellent comment of @AMR. The real sheet of paper will have a different reflectance spectrum. Hence, both photo and real sheet will be interpreted as a function of ambient lighting by your visual system and they will appear different.

Even when your image was printed as a photo, the color is obviously different from the white sheet of paper. So the ambient light has a different effect on the reflectance spectrum of the photo and the real sheet.

Also the global contrast is different: the photo with a different spectral content than the real sheet is re-placed into the context of ambient lighting. Hence, the photo it is out of context and will be re-interpreted.

Reference
- Mather, Foundations of perception and sensation 2nd ed. Psychology Press 2008


Colour measurement instruments

6.2.1 Colorimeters

A colorimeter can measure the absorbency of light waves. During colour measurement the change in the intensity of electromagnetic radiation in the visible wavelength region of the spectrum after transmitting or reflecting by an object or solution is measured. Such a measurement can help to find the concentration of substances, since the amount and colour of the light absorbed or transmitted depends on the properties of the solution, including the concentration of particles in it. A colorimeter is an instrument that compares the amount of light getting through a solution with the amount that can get through a sample of pure solvent. A colorimeter contains a photocell which is able to detect the amount of light passing through the solution under investigation. The current produced by the photocell depends on the quantity of light hitting it after passing through the coloured solution. The higher the concentration of the colorant in the solution, the higher is the absorption of light less light passing through the solution means less current created by the photocell. A colorimeter takes three wideband readings along the visible spectrum to obtain a rough estimate of a colour sample. Traditionally, the word ‘colorimeter’ is used for a device, having three filters, that simulates human vision. Colorimeters can be classified into two types:

Visual colorimeters are of two types:

Visual absorption meters/colour comparators

True visual colorimeter or tristimulus colorimeter.

The former type compares the colour of the test sample, usually liquid, with that of standard and finds a match between the two. Such instruments are employed for chemical analysis, concentration determination, and grading on the basis of colour.

The tristimulus colorimeter emphasises visual equivalence or psychophysical estimation (see Section 7.2 ). In this instrument, radiant power from the light source is incident onto the object. The reflected radiant power passes through one of the three tristimulus filters and falls onto the photo-detector, causing it to give a response proportional to the corresponding tristimulus value of the object-source combination. This raw data is then transferred to a microprocessor for the computation of the absolute CIE tristimulus values. It is a useful tool for monitoring the production of a coloured object. Most commercial tristimulus colorimeters are satisfactorily precise, but their measurements may not agree with the tristimulus values obtained by spectrophotometry.

The oldest and simplest colour comparator is the Nessler tube, which was developed into the Duboscq colorimeter. This type of colorimeter can compare only the optical properties of solutions of a particular colouring substance, but this is all that is required in many colour-assessment tests. Figure 6.2 shows the construction of the instrument. There are two vertical cells which accommodate the reference and test solutions, having the same colorant but of different concentrations. Two movable glass plungers can be operated to vary the path lengths L1 and L2 of the absorbing solutions until the colours in both fields in the eyepiece appear the same. Applying the Beer–Lambert law, the concentration of the unknown solution can be determined by multiplying concentration of the known solution with the ratio of path lengths. According to the above law, when the colour of both solutions appears equal, each of the light beams must have passed through the same number of molecules, and the number is directly related to the concentration of the solution multiplied by the path length ( Equation [6.1] ), i.e.

If the concentration C2 is known, we can easily calculate the other concentration. The accuracy of the measurement depends on the visual perception of the observer. Hence in Hilger–Spekker absorption meter, visual assessment was replaced by measurement with photoelectric cells. A calibrated light gate was adjusted till the electrical output matched that for the test light. The equality was assured when there was no deflection of the galvanometer.

True colorimeters define colours in terms of their own primaries. A number of colorimeters were specially developed for colour vision research. These were very elaborate, costly and highly specialised to serve one or a limited number of purposes. The earliest true colorimeter was Clerk Maxwell’s colour box (1860), consisting of a prism unit with adjustable slits in the appropriate parts of a light path to control independently the amounts of red, green and blue light beams viewed as a homogeneous colour in an optical viewing unit to match the colour of the sample shown in the other half of the optical unit. The relative aperture areas x, y and z were recorded as the amount of the three primaries.

Three famous visual tristimulus colorimeters used in Great Britain for research on various aspects of normal colour vision were those of Guild (1925) , Wright (1927) and Donaldson (1935) . Guild used an incandescent source and three colour filters. Donaldson used similar colour filters. Wright used an elaborate optical system to separate three wavelengths, namely 460, 530 and 650 nm, from white light to use as primaries. However, they produce a metameric match, and the results vary from observer to observer. Donaldson (1947) modified the instrument by using six primaries to overcome the problem of metamerism. The instrument was used for field trials on the 2° and 10° colour-matching functions ( Wyszecki, 1964 ). It lost its popularity owing to the difficulty in calibration and its poor field illuminance. However, some of its basic features have been retained in the designs of other instruments.

MacAdam’s Binocular Colorimeter ( MacAdam, 1950 ) provided a large bipartite field for simultaneous viewing by both eyes. The instrument consisted of two symmetric parts, each of which could be used for spectral match with the colour stimulus by the other part. Wyszecki’s seven-field colorimeter ( Wyszecki, 1965 ) was designed with an array of seven visual fields for viewing with both eyes. The instrument was developed mainly for research where more than two visual fields were necessary, such as study on colour difference matching, colour-matching ellipses, hue matching, etc.

None of the above colorimeters was commercialised, because they were not very attractive in terms of cost, time and skill required. The Burnham colorimeter ( Burnham, 1952 ) is relatively simple in construction and utilises additive mixing of primary stimuli, made up of coloured filters and a light source. A transparent disc ( Fig. 6.3 ) is divided into three sectors bearing coloured filters, red (R), green (G) or blue (B). The disc is free to rotate about a central axis, and the axis can move horizontally, varying its position with respect to a stationary circular beam of white light shown by a small circular aperture plate, the centre of which has the same vertical position as the centre of the disc. After passing through the disc, light from the beam is mixed by multiple reflections:

6.3 . Burnham colorimeter with red, green, blue filters and aperture plate. (Different quantitites of R, G and B in mixture give white, yellow, orange and other colours.)

When the beam and disc are concentric, rotation of the disc is without effect. The transmission of the filters and their relative angular size can be adjusted so that the mixture has the coordinates of a suitable reference white ( Fig. 6.3a ).

As the disc is moved horizontally within the beam, the relative portions of the three primary colours change ( Fig. 6.3b ).

Rotation of the disc changes colour ( Fig. 6.3c ).

The saturation of the colour varies monotonically with the eccentricity of the disc.

The Lovibond comparator is a type of colorimeter made in Britain by The Tintometer Ltd. It was invented in the nineteenth century by Joseph Williams Lovibond and updated versions are still available. The Lovibond colorimeter (1870–1880) is still a popular commercial visual colorimeter, even after 100 years of use and development ( Lovibond, 1887 Chamberlin and Chamberlin, 1980 ). Lovibond colorimeters are used in the analysis of products such as edible and industrial oils, oil derivatives, liquid chemicals, paint vehicles and coatings. They are based on subtractive colour mixing of coloured glass filters. There are 250 Lovibond glass filters for each of three primaries, namely magenta, yellow and cyan, of a very permanent nature. The filters are graduated in such a way that two ‘1.0’ glasses match a ‘2.0’ glass plus a colourless glass. Equal values of all three together give a grey series down to black.

Putting suitable Lovibond filters in the light filters in the light path, nearly nine million colours of varying brightness can be matched. In fact, the whole visible colour gamut can be covered, except the highly saturated green area. This area can now be covered using a cyan illuminant in the matching field instead of normal north daylight light source. The colour is assessed by visual matching of samples such as surface colours or transparent samples, including liquids kept in the sample field and the coloured filters on the path of illuminating light in the reference field. Automatic Lovibond instruments, which overcome the subjectivity of visual methods, are now available. The menu system guides operators through the selection of operating parameters. Thereafter, measurements are initiated by just a single key press and take less than 25 s to complete. Use of sample cells up to 6" path length ensures precise colour measurement, without multiplying errors, even with unsaturated samples. Sixteen interference filters are used for measurements in some automatic machines.


SpyderX Elite – same color on different screens

When two or more monitors are calibrated with a sensor like SpyderX and the software reports a successful calibration and the monitors don’t match visually – is there something wrong with the calibration?

Matching two monitors requires us to keep in mind five important points that we describe within the next few pages. One important thing that we want to mention right in the beginning of this article: You need a flexible and accurate calibration tool that is made for technically matching and visually tuning the color output of computer monitors, such as SpyderX Elite.


Point 1:
If you want to match monitors, consider that they mostly differ physically. Monitor calibration will optimize and correct color output on a display, but it is not able to improve the physical quality. If one of the devices is a wide gamut monitor (which covers AdobeRGB) while the other covers a standard gamut only (sRGB), then higher saturated color outside sRGB can’t be reproduced by that standard monitor. Colors within the sRGB color space are covered by both and can be matched closely by following this article.

Point 2: Room light conditions as well as any color surrounding your monitor will influence your color perception. For this reason, it is very important to keep all conditions equal. This includes even the color of the background behind the monitors and the desk’s color. Also, the angle of view often changes the color perception. Simple displays with TN panel technology are more affected than better IPS panels, for instance.

Point 3: The computer system needs to handle all connected and monitors that are being used with full color management capabilities. This includes white point correction as well as linearization of the color primaries via LUT (Look Up Table) of the video card. While the white point will be handled by the image editor or browser, the linearization will be flashed to the LUT of the video card. It is important that the video card needs a separate LUT for each connected monitor.

Point 4: Some software tools don’t support color management. Microsoft’s Internet Explorer is one example, as is the Preview tool in Windows. The latest Firefox, Photoshop (all versions), Lightroom or other image editors handle color spaces extremely well. Only an overlapping window (between two monitors) won’t work, even when using one of the properly working tools mentioned. Opened files need to stay on one display only. In this case, when a file is moved from one monitor to the other, the full color correction will be applied in the moment you drop it (releases the mouse button) onto the appropriate monitor.

Point 5: Visual matching will always be necessary if you want to match monitors. This has nothing to do with the calibrator, rather it’s about human color perception. This is affected by personal white point correction. Like a camera, the human eye can only compensate one light source type at a time. But if there are two monitors side by side, they will differ in their color spectrum (even if both devices are LED screens). In the images on the right side, the white point was first set to daylight, second to the CCFL lights in the right showcase and third to the halogen lamps in the left showcase. The same effect occurs using two monitors – sometimes more, sometimes less. The human eye (here it was the camera) always compensates for the white point of the main light source, which is mostly the bigger and brighter monitor right in front of the user. In the same moment, the white point compensation doesn’t fit to the second monitor anymore. This can’t be corrected by a sensor, because this is an individual compensation, varying from person to person. The only way to match the second monitor to the primary one is to visually adjust the correct calibrated monitor in terms of its white point to the main monitor. Because this will be done in a linear way with the feature “SpyderTune”, the calibration will keep its accuracy, but match the white point as best as possible.

Here’s the whole process step by step:

This all starts in a dimly lit room set to approximately 100 LUX. (The reason why this is necessary and how to ensure the best possible room light level is described on the following page.) Now calibrate the monitors with SpyderX Elite and its StudioMatch feature. As long as the color space of the photo workflow is sRGB or AdobeRGB, the calibration target will be 6.500k color temperature and Gamma 2.2. The monitors should be calibrated to a luminance of 120 cd/m 2 . After these two calibration processes, the monitors are technically calibrated and matching. Due to the different light sources (see Point 5 above) users will see a difference in the white point. To compensate for that, use the feature “SpyderTune” to visually match the secondary monitor to the primary one. It is important that the main display stays as is and not adjusted after its calibration.

  1. Start in a very low room light (approx. 100 LUX)
  2. Calibrate monitors with SpyderX Elite and StudioMatch
  3. Calibrate primary monitor to the following target:
  • 6.500k color temperature
  • Gamma 2.2
  • 120 cd/m 2
  1. SpyderTune to match the secondary monitor visually to the primary monitor

1, 2, 3 – if number 1 is visible: clearly=monitor too bright – very barely=luminance is good – not visible=monitor too dark and/or room light too bright

Why room light conditions are so important

It’s really important to work in a dimly lit room – here’s why: Imagine that you are sitting in a pitch dark room, looking on your monitor showing a dark gray cross (RGB 4, 4, 4) on a black background (RGB 0, 0, 0) – you can barely see it. But what if you move your monitor in direct sunlight? Can you still see the cross? No, it’s not visible anymore, but what happened? The sunlight is so bright that your eye’s iris reduces the size of your pupil to a very small aperture. As a photographer you know that f22 is not the correct aperture to work in the darkness. So, your monitor shows you details, but you aren’t able to see it – that’s why post-production needs to be done in dim, ambient light.

Here’s an easy way to measure your room light: Take your camera and set it to the “S”-mode. Now set it to ISO 100 and your shutter speed to 1.0 second. (Be sure to set your exposure compensation to 𔃰’.) Now cover your monitors with a cardboard or switch them off and focus your camera on your desk area. Then check which aperture value is automatically used by your camera. If this is between f4.0 and f5.6, your room light is a perfect level (around 100 LUX) to do image editing and post production.


Why are most metals gray/silver?

Why do most metals appear silver in color, with gold being an exception?

It is hardly surprising that the answer to this question relies heavily on quantum theory, but most people will be surprised to hear that the full answer brings relativistic considerations into the picture. So we are talking quantum relativistic effects.

The quantum bit of the story tells us that the colour of metals such as silver and gold is a direct consequence of the absorption of photons by d electrons. This photon absorption results in d electrons jumping to s orbitals. Typically, and certainly for silver, the 4d→5s transition has a large energy separation requiring ultraviolet photons to enable the transition. Therefore, photons with frequencies in the visible band have insufficient energy to be absorbed. With all visible frequencies reflected, silver has no colour of its own: it's reflective, an appearance we refer to as 'silvery'.

Now the relativistic bit. It is important to realize that electrons in the s orbitals have a much higher likelihood of being in the neighborhood of the nucleus. Classically speaking, being close to the nucleus means higher velocities (cf speed of inner planets in solar system with that of the outer planets).

For gold (with atomic number 79 and hence a highly charged nucleus) this classical picture translates into relativistic speeds for electrons in s orbitals. As a result, a relativistic contraction applies to the s orbitals of gold, which causes their energy levels to shift closer to those of the d orbitals (which are localized away from the nucleus and classically speaking have lower speeds and therefore less affected by relativity). This shifts the light absorption (for gold primarily due to the 5d→6s transition) from the ultraviolet down to the lower frequency blue range. So gold tends to absorb blue light while it reflects the rest of the visible spectrum. This causes the yellowish hue we call 'golden'.

Reflectivity as function of wavelength. Purple/blue light corresponds to 400 - 500 nm, the red end of the visible spectrum to about 700 nm.

D electrons in metals allow optical transitions in the visible regime. Visible light can be absorbed by elements having unbound valence electrons in the d shell. So

Chemistry: optical d->s$^2$ transition

  • Iron [Ar] 3d$^6$ 4s$^2$
  • Tin [Kr] 4d$^<10>$ 5s$^2$ 5p (full d shell)
  • Aluminium [Ne] 3s$^2$ 3p$^1$ (is a special case: no d valence electrons, but Aluminium reflectivity. I have no other explanation than the calculation of Fresnel equations. However I can't grasp the reason for this distinction.)
  • Lead [Xe] 4f$^<14>$ 5d$^<10>$ 6s$^2$ 6p$^2$ (full d shell)
  • Zinc [Ar] 3d$^<10>$ 4s$^2$ (full d shell)
  • Tungsten [Xe] 4f$^<14>$ 5d$^4$ 6s$^2$
  • Nickel [Ar] 4s$^2$ 3d$^8$ or 4s$^2$ 3d$^9$
  • Copper [Ar] 3$d^<10>$ 4$mathbf$ (one s and full d shell)
  • Gold [Xe] 4f$^<14>$ 5d$^<10>$ 6$mathbf$ (one s and full d shell)

The shiny metals, except aluminium, have d electrons. A single s electron and a full d shell hint at an important d to s$^2$ orbital transition in the visible spectrum. A full s shell is energetically preferred. There seems to be no explanation for the colored appearance of gold and copper, other than a distinctive electron configuration - at least chemistry does not provide an answer.

Physics: sign change of $epsilon(lambda)$ near blue

If the absorbed light is reemitted (in fact reflected) for the whole visible spectrum, the metal appears shiny as a mirror. In fact, our bathroom mirrors are made of an aluminum backside coated glass.

Here physics has to explain more than just "is there a d valence electron". A second more physical reason doesn't describe its origin: Reflectivity, out of the Fresnel equations using $n=sqrtqquad extqquad epsilon_r=1-fracqquad extqquad omega=omega_p $

out of the Drude free electron gas model for electrons (and density of electrons $n_e$), is high through the whole visible spectrum for these metals. This sign change at $omega=omega_p$, plasma frequency is the reason for a changing $epsilon_r$, therefore a changing refractive index $n$, due to the Fresnel equations, a changing reflectivity. If this change happens to be in the visible spectrum, then there are colored reflections like gold. Blue absorption of gold happens, because special relativity has to be taken into account for this heavy element. See top answer. Copper and Gold don't have a high reflectivity for blue ($approx 475,$nm).

"The color of metals can be explained by band theory, which assumes that overlapping energy levels form bands.

In metallic substances, empty conduction bands can overlap with valence bands containing electrons. The electrons of a particular atoms are able to move to a higher-level state, with little or no additional energy. The outer electrons are said to be "free," and ready to move in the presence of an electric field.

The highest energy level occupied by electrons is called the Fermi energy, Fermi level, or Fermi surface.

Above the Fermi level, energy levels are empty (empty at absolute zero), and can accept excited electrons. The surface of a metal can absorb all wavelengths of incident light, and excited electrons jump to a higher unoccupied energy level. These electrons can just as easily fall to the original energy level (after a short time) and emit a photon of light of the same wavelength.

So, most of the incident light is immediately re-emitted at the surface, creating the metallic luster we see in gold, silver, copper, and other metals. This is why most metals are white or silver, and a smooth surface will be highly reflective, since it does not allow light to penetrate deeply.

If the efficiency of absorption and re-emission is approximately equal at all optical energies, then all the different colors in white light will be reflected equally well. This leads to the silver color of polished iron and silver surfaces.

For most metals, a single continuous band extends from valence energies to 'free' energies. The available electrons fill the band structure to the level of the Fermi surface.

If the efficiency decreases with increasing energy, as is the case for gold and copper, the reduced reflectivity at the blue end of the spectrum produces yellow and reddish colors.

Silver, gold and copper have similar electron configurations, but we perceive them as having quite distinct colors.

Gold fulfills all the requirements for an intense absorption of light with energy of 2.3 eV (from the 3d band to above the Fermi level). The color we see is yellow, as the corresponding wavelengths are re-emitted.

Copper has a strong absorption at a slightly lower energy, with orange being most strongly absorbed and re-emitted.

Silver. The absorption peak lies in the ultraviolet region, at about 4 eV. As a result, silver maintains high reflectivity evenly across the visible spectrum, and we see it as a pure white. The lower energies corresponding to the entire visible spectrum of color are equally absorbed and re-emitted making silver a good choice for mirror surfaces.


Color & Heat Absorption


This is a compilation of information from students who are conducting scientific color experiments about color and heat absorption.

Questions:
#1 - I am doing a science fair experiment on color vs. heat absorption. I need ideas on research.
#2 - When using a thermometer, is it better to use cloth or construction paper?
#3 - Is it better to use a light source or the sun? Ben Franklin's research with cloth and snow sounds interesting. Has anyone tried to set that one up?

Best Scientific Answers
Color and Heat Absorption - from "Ask a scientist"
Color and Heat Absorption - from MadScientst Network
Best Student Experiment

Heat Absorption and Emissivity - Information from others


JP : As you probably already know, dark colors (black) will heat up more than light colors (white). Try using thermometer strips sold at pet stores (to stick on the insides of reptile cages to monitor temperature). They're cheap, don't break, are flat so you can put them under a piece of paper (if that's what material you're using) to check your temperatures. Try some materials with different reflective surfaces too (foil shiny black vs. rough-surfaced black for example).

Chris Willard : I would follow Ben Franklin's observations, put different colors on a block of ice (he used snow). Set the ice in the sun and observe how the darker colors melt down into the ice faster (presuming it will, I've not tried this). another idea might be to set a thermometer under pieces of cloth that are set in the sun or under a lamp to measure different temperatures.

Anonymous: White reflects more energy than black does. Absorbed energy is of course not destroyed but usually converted to heat so the answer to your question is yes, makes a difference.

Mac : Color can affect heat absorption because of emissivity. A number of variables can enter into the picture, so if you conducted an experiment, you'd need to proceed carefully, to avoid skewed results. Emissivity would probably be the key differentiator in your question. (Look up emissivity in the dictionary).

Given two identical glass containers - one being of one color A and another being of another color B and that they would be filled with, say, some identical heated liquid, and then allowed to cool -

And given that the emissivity of container colored A and the emissivity of container colored B is substantially different, then the rates of cooling would be different. [You would need to measure or otherwise determine what the 'emissivity' of each specifically colored glass is.]

Emissivity of materials is of significant concern in some industries - for instance - if you are building a spaceship - and you want to keep parts of the spaceship cool or other parts warmer. The 'color' (more precisely, the emissivity) of the surface of the ship will determine whether that portion of the spaceship will be cold, cool, warm, or hot.

There are lists that give the values of emissivity of various materials - in books on spacecraft design, thermal properties handbooks, and similar texts.

Two of the main attributes you would want to look at in an experiment that would demonstrate this would be 1. the material's emissivity and 2. the material's thermal conductivity.

To remove multiple external variables from your experiment - you might want to place both of the glasses of liquid into a black box (keeping them out of sunlight/away from external heat / light sources). Don't put them in the microwave either! :-)

And if do perform an experiment - if you use two thermometers or thermocouples, be sure they are calibrated. And gosh - publish your findings here if you do perform the experiment.

If you paint one glass Black and the other glass White, which container do you think will cool faster? Any hunch?

Anonymous: About the absorption of heat and emissivity in coffee cups: The cups would take heat energy from the coffee at same rate, given same material of cup, as this is conductive heat transfer, while the white cup will radiate heat to surrounding air more slowly than the black cup, and so in total the black cup of coffee will cool down quicker.

An excellent student experiment about color and heat absorption

The following is documentation of a student's experiment with color and heat absorption. We only know her as "Madeline" and here's the research that she posted on the bulletin board at Color Matters, January, 2000.

Question
Does the amount of thermal energy (heat) produced by a colored fabric after 30 minutes of intense light relate to its position in the spectrum?

Hypothesis
When a color (colored fabric) absorbs light, it turns the light into thermal energy (heat). The more light a color absorbs, the more thermal energy it produces. Black fabric absorbs all colors of light and is therefore warmer than white fabric which reflects all colors. I predict that the colors of the spectrum appearing the darkest and most like black (violet, indigo, and forest green) will produce the most thermal energy. The other colors (red, orange, and yellow), will produce the least thermal energy because they appear lighter or more like white.

Materials
1. a thermometer (preferably an indoor/outdoor thermometer because they have the largest temperature range)
2. a 1&rsquo x 1&rsquo piece of heavy corrugated cardboard
3. tape
4. a clock, stopwatch, or timer
5. sunlight (If you&rsquore short on sunlight, use a with a halogen floodlight, at least 100 watts. A halogen bulb is a good choice because it has a high light intensity and its light spectrum is very similar to sunlight.)
6. six 100% cotton T-shirts (or pieces of cloth) in red, orange, yellow, forest green, indigo, and violet

Procedure
A simple way to measure how much thermal energy a colored material produces is to measure the changes in its temperature:
1. Tape the thermometer in the center of the cardboard. Make sure the tape doesn&rsquot cover the thermometer bulb.
2. Set the cardboard/thermometer indoors, out of direct sunlight.
3. Lay the red cloth over the cardboard/thermometer so it is touching the thermometer bulb.
4. Set the lamp so the bulb is 2 feet away from and perpendicular to the cardboard/cloth.
Turn the lamp on.
5. Position the cardboard/cloth so the thermometer bulb is in the center of the beam of light.
6. Wait 30 minutes, then record the temperature under the cloth.
7. Turn the light off and take the cloth off the cardboard.
8. Repeat steps 3 through 8 using each of the other colors of cloths. (Orange, yellow, forest green, indigo, violet.)
9. Repeat the experiment at least 6 times and calculate the average temperatures for each color.

Conclusion
My hypothesis is correct. The darker colors (forest green, indigo, violet) produced the most thermal energy after 30 minutes of intense light. The lighter colors (red, orange, yellow) produced smaller amounts of thermal energy. (The average recorded temperature (°F) for each of the colors is shown in Graph 1.) Interestingly, the temperatures of the fabrics fell in to two groups instead of increasing as the colors got closer to violet. The difference between the temperatures of the red, orange, and yellow fabric was minimal, only 10ths of a degree. The same thing was true for violet, indigo, and forest green fabric. However, the difference between the temperatures of the two groups was a little more than 3 degrees (Fahrenheit). In conclusion, even though violet, indigo, and forest green are generally referred to as "cool" colors, you will be warmer if you wear them! You may not be any warmer if you wear blue instead of green, or green instead of purple. Similarly, it won&rsquot make a difference if you wear red instead of yellow, or yellow instead of orange, but on a hot day, wear one of the warm colors!

Bibliography
Gardner, Robert. Science Projects About Light. Springfield, New Jersey: Enslow Publishers, Inc., 1994, p. 92
Morton, J.L. Color Matters - ElecroMagnetic Color - 1995-1999

About Light
There are many different kinds of light. The different kinds have different wavelengths. Ultraviolet light, for example, has a wavelength of 10-8 meters. Visible colors have a wavelength of about 10-6 meters, the diameter of a bacteria. Infrared light also has a wavelength of about 10-6 meters, but has a longer wavelength than the visible colors. The different colors of visible light have different wavelengths, but the wavelengths are very similar. Violet light has the shortest wavelength, is the coolest, and is closest to ultraviolet light. Red light has the longest wavelength, is the warmest, and is closest to infrared light. The other colors of visible light increase in wavelength and warmth as they get closer to red and infrared light. (For example, yellow light has a longer wavelength and is warmer than indigo light.)

When you shine white light (the light that includes all the visible colors) on a colored object, the object will appear to be the color of the light it reflects. All the other visible colors are absorbed. If the object reflects a warm color (red, orange, yellow) it will be cooler than an object which absorbs them. For example, if you shine light on a blue object, it will absorb the warm red light, and will be warmer than a red object which would reflect that light.

Results of Experiment (completed 8 times)

Cloth Color Red Orange Yellow Dk. Green Indigo Violet
Temperature( F) 76 77 76 80 81 78
78 76 77 76 82 78
76 77 78 83 79 82
76 79 77 80 81 84
78 78 76 86 83 82
78 75 78 81 82 80
78 78 79 79 78 84

77 77 77 81 81 80 Standard Deviation 0.991031 1.246423 1.035098 2.915476 1.642081 2.390457
Average Temp. ( F) 77.13 77.13 77.25 80.75 80.88 81



Does a pink jail cell calm an angry prisoner? Will a pink locker room make a football team weak? Find out at Color Matters: Drunk Tank Pink

Links to More Science Projects

Here's a compilation of all the pages with information from students who are conducting scientific color experiments.

You might also be interested in .

Does a pink jail cell calm an angry prisoner? Will a pink locker room make a football team weak? Find out at Color Matters: Drunk Tank Pink


What shade of light grey can be seen on 99% of monitors?

I'm working from a design where the grey shade F0F0F0 is used as a subtle contrast on list items to lift them from the pure white background, eg:

I have a two monitor setup, and on one monitor, I can see the grey background of the cards, on the other I can't. The problem monitor has no built in or driver based hue/saturation/gamma settings. Playing with contrast and brightness doesn't help

My guess is there is some percentage of users who have a similar monitor, and even more who could configure their monitor but simply don't know that they should, or how to do it.

Now the solution would be to darken the grey - but I want to find the sweet spot where as many users as possible can see the grey without making it too dark to be subtle on well calibrated monitors.

Has anyone dealt with this before and have some suggestions - or are there any statistics on safe shades of grey to use on the web.

Here is a blog post talking about the same problem

I came across the material design color palette. Looking at the grey scale they provide, I see that 50, 100 and 200 look the same on my bad monitor, but the difference between 200 and 300 is noticeable yet subtle on both the calibrated and bad monitor :

Is this the case on anyone else's monitor? Then maybe using a light grey(200) as background instead of white, with a darker grey for items(300). It would be a minimal change for correctly calibrated monitors, but may improve the design's visibility for the average monitor.


Update 2021-01-29

I’ve added several more color spaces to the widget above.

One of the color spaces is linear mixing, which doesn’t have great hue linearity, and is perceptually way too light in the white-black ramp. But I include it for comparison because some have suggested that it is appropriate for gradients.

Another great resource for “better gradients” is Matt Deslaurier’s gradient Observable notebook. That now has an open source license and a correct implementation of XYB.

The XYB color space is part of JPEG XL, and thus its main motivation is image compression. Its hue linearity is not great, about halfway between CIELAB and IPT. However, it has a nice transfer function - it’s a cube root with an offset, which has generally similar darkness/lightness as CIELAB, but with smoother derivatives throughout. If I were to make a new color space, I would choose this transfer function.

SRLAB2

A very little known color space is SRLAB2 by Jan Behrens. It uses the CIELAB transfer function but updates the matrices for better hue linearity. Overall it performs very well the only flaw I found is that the red-white ramp bends toward orange (as does CIELAB).

Juha Järvi has produced a gist analyzing SRLAB2 in more detail, and there is some Reddit discussion as well. Thanks to Juha for bringing this to my attention.


Is That Dress White and Gold or Blue and Black?

Our perception of color depends on interpreting the amount of light in a room or scene. When cues about the ambient light are missing, people may perceive the same color in different ways. Related Article

A photograph of a dress on Tumblr prompted an Internet discussion: What color is it?

Some people see a white and gold dress in dark shadow.

Some people see a blue and black dress washed out in bright light.

Some people see one interpretation and then switch to the other.

The striped dress takes up most of the frame in this photo. If we take two pieces of the dress and average the colors in Photoshop, we get a flat pattern of color:

How Do We Interpret Those Colors?

Our eyes are able to assign fixed colors to objects under widely different lighting conditions. This ability is called color constancy. But the photograph doesn&rsquot give many clues about the ambient light in the room. Is the background bright and the dress in shadow? Or is the whole room bright and all the colors are washed out? Different people may pick up on different visual cues in the image, which can change how they interpret and name the colors.

IS THE DRESS IN BRIGHT LIGHT?

If you think the dress is in shadow, your brain may remove the blue cast and perceive the dress as being white and gold.

If the photograph showed more of the room, or if skin tones were visible, there might have been more clues about the ambient light.

If you think the dress is being washed out by bright light, your brain may perceive the dress as a darker blue and black.

Other photographs show that the dress is actually blue and black. In this second photograph, the white wedding dress, dark curtains, visible skin tones and body shadows help us accurately judge the amount of ambient light in the room.

A photograph of a dress on Tumblr prompted an Internet discussion: What color is it?

Some people see a white and gold dress in dark shadow.

Some people see a blue and black dress washed out in bright light.

Some people see one interpretation and then switch to the other.

The striped dress takes up most of the frame in this photo. If we take two pieces of the dress and average the colors in Photoshop, we get a flat pattern of color:

How Do We Interpret Those Colors?

Our eyes are able to assign fixed colors to objects under widely different lighting conditions. This ability is called color constancy. But the photograph doesn&rsquot give many clues about the ambient light in the room. Is the background bright and the dress in shadow? Or is the whole room bright and all the colors are washed out? Different people may pick up on different visual cues in the image, which can change how they interpret and name the colors.

If you think the dress is in shadow, your brain may remove the blue cast and perceive the dress as being white and gold.

If the photograph showed more of the room, or if skin tones were visible, there might have been more clues about the ambient light.

IS THE DRESS IN BRIGHT LIGHT?

If you think the dress is being washed out by bright light, your brain may perceive the dress as a darker blue and black.

Other photographs show that the dress is actually blue and black. In this second photograph, the white wedding dress, dark curtains, visible skin tones and body shadows help us accurately judge the amount of ambient light in the room.


2 Answers 2

It's kind of a funny misconception that the sun is yellow. I mean, astronomically speaking it is indeed a yellow star, more precisely G-type main sequence / yellow dwarf. but don't be fooled by the terminology: astronomically speaking, you'll also find that the Earth consists completely of metal!

Actually you should consider the sun as white.

The main reason, strangely enough, why we think the sun is yellow is that we never look at it. That is, directly enough to judge its colour. When the sun is high in a cloudless sky, it's just too bright to see its colour (and evolution has trained us to not even try, because it would damage the eyes). Only near sunrise or sunset do we actually get to look at the sun, but then it's not so much the colour of the sun but the colour of the atmosphere we're noticing – and the atmosphere is, again counter to perception, yellow-orange-red in colour. Well, not quite – the point is that the atmosphere lets red / yellow light through in a straight line whereas bluer frequencies are more Rayleigh scattered. That's the reason why the sky is blue, and also adds to the perception of the sun being yellow: it's yellow-ish in comparison with the surrounding sky colour.

When you see the sun through clouds, you get to see its actual colour more faithfully than usual, both because (as Mark Bell wrote) Mie scattering doesn't have the colour-separating effect that Rayleigh scattering does, and because you then see it against a grey / white backdrop instead of against the blue sky.


1) Luminance / Brightness Level

One thing to know about monitor luminance (or brightness, in simple terms) is that it&rsquos typically the only genuine hardware adjustment you can make to an LCD monitor. You are basically altering the backlighting with a dimmer switch.

The above is only untrue if you select a luminance setting that is lower than your monitor can naturally reach, in which case a software adjustment comes into play. Ideally, you don&rsquot want this, since it eats into the monitor&rsquos gamut (the range of colors it produces) and leaves it open to problems such as banding.

Always use software that tells you how bright the monitor is and lets you adjust it interactively.

Software versus hardware

Software adjustments are the ones that go through the graphics processor, while hardware adjustments are those that bypass the GPU and address the monitor directly. The former may cause problems in some cases, which is useful to bear in mind. Expensive monitors tend to allow more in the way of hardware calibration, enabling a higher image quality.

What setting to use?

Monitor luminance is measured in candelas per square meter (cd/m2), sometimes referred to as &ldquonits&rdquo. A new LCD monitor is usually far too bright (e.g. over 200 cd/m2). Aside from making screen-to-print matching hard, this reduces the monitor lifespan.

You need a calibration device to measure the luminance of your monitor and always return it to the same level, as the backlighting slowly degrades. The trouble with using onscreen monitor settings to do this (e.g. 50% brightness) is that their meaning changes over time.

The arbitrary setting

Although arbitrary, the 120 cd/m2 setting that most software defaults to is a fair place to start. Most monitors can reach that level using the OSD brightness control alone, without resorting to reducing RGB levels and gamut. The setting you use is not critical unless you are explicitly trying to match the screen to a print or print-viewing area.

Dictated by ambient light

Ideally, you should control the ambient lighting in your editing area so you&rsquore free to set the luminance you want. The monitor should be the brightest object in your line of vision. If you&rsquore forced to edit in a bright setting, luminance must be raised so that your eyes are able to see shadow detail in your images. Some calibrators will read ambient light and set parameters accordingly. In controlled situations, this feature is needless and even unhelpful.

The paper-matching method

Many printers set their monitor luminance very low. By this, I mean between 80-100 cd/m2. The idea is to hold a blank piece of printing paper up next to your screen and lower the luminance until it matches the paper, or just set a low level so that this is more likely.

Potential downsides include a degraded monitor image since not all monitors can achieve this low luminance level without ill effect. Still, you could try it. This is about finding what works for you and your gear.

Matching the print-viewing area

Another way printers set monitor luminance is to match it to the lighting of a dedicated print-viewing booth or area. Although the light in this area may differ to that of the final print destination, it&rsquos useful to note that monitor calibration is never quite an exact science. As well, print display lighting is always adjustable in its intensity. Using this method, the monitor luminance might be as high as 140-150 cd/m2. This setting should be natively achievable by any monitor.


Set Up Color Calibration Setting For Color Management

This is my third post in a series of tutorials, essays, and videos that aim to mystify Colour Management. The first article gave a general overview of the topic, and the second dealt with the mundane topic of Color Settings in Photoshop. As ever I will stick to the essentials in hoping to be clear and concise.

Colour Management is the art and science of predictably translating environmental colours through digital input devices into reliable, high-fidelity, output. An essential part of the colour workflow is your monitor. Not only should it be fit for purpose, you will need to tune it up. Monitors need to be calibrated and profiled to give predicable results. Calibration is setting devices to an appropriate set of values. Profiling is a record of the colours available in a device whether that is your camera, printer, or monitor. Using profiles aids the translation of colour from one device to another.

Colour Management helps make colour translations predictable, because there is really no such thing as totally accurate colour matching system. The tonal range of monitors vary depending on the type of monitor used, and the tones and colour of a print are dependent on the printer and paper used.


Watch the video: Warum gibt es Farben? - Einfach erklärt Gehe auf u0026 werde #EinserSchüler (December 2022).