Introduction
Do the three images below look identical? If they look different (probably very different,
see example), it means that your browser does not display color correctly.
[Click on each image to see a larger version.]
| sRGB |
Adobe RGB |
ProPhoto RGB |
 |
 |
 |
 |
 |
 |
The tables below capture the browser support for color spaces as of June, 2007. Should the results concern
you? Probably not, unless you encounter a page where the site author (probably a photographer) indicates that
something other than sRGB is used, such as Adobe RGB.
| MacOS 10.4.4 |
| Browser |
Color Space Support? |
| Safari 2.0.x |
Yes |
| Firefox 1.5.0.12/2.0 |
No |
| Internet Explorer 5.2.3 |
No |
| Windows XP |
| Browser |
Color Space Support? |
| Apple Safari 3 beta |
Yes |
| Firefox 1.5 |
No |
| Internet Explorer 6.0 |
No |
| Netscape 7.1 |
No |
Windows users can download Safari 3 beta at apple.com/safari.
Discussion
When using a web browser, the accuracy of the color and the density (brightness) of an
image depends on a number of factors.
- Whether the display is color-managed, with reasonably accurate calibration and profiling;
- Whether the browser properly interprets the color space of an image;
- Ambient lighting;
- The viewer’s eyesight (eg color-blindness).
Excepting Apple’s Safari, images look reasonable on the millions of PCs
out there just by pure luck; a browser can only display sRGB images correctly if it can display images of all color
spaces correctly; the task is the same. It’s only because virtually all images on the web are in the sRGB
color space and most monitors display something reasonably close to sRGB that images in a web
browser look anything like they’re supposed to.
A computer display that has not been calibrated and profiled will produce
a rendition of an image which may or may not look very much like it should. It might be too dark or too light,
and the colors might shift significantly. By comparison, a high-quality calibrated and profiled system should
display images very accurately. A high-quality display can also display a wider range of color (gamut)
than a cheap one. Even so, no display can reproduce anything close to the range of color the human eye can
discern.
Most web browsers assume that the color space of
an image is sRGB, a commonly-used color space which is the de-factor standard for web use. Such images
will display accurately in a web browser (within the limits of the monitor and whether it has been calibrated and
profiled). An image which uses another color space, such as Adobe RGB or ProPhoto RGB may
look very different unless the image is tagged with that color space and the web browser reads that tag
to correctly display the image. The gripe that photographers have with sRGB is that it has a relatively
small gamut—meaning that it cannot reproduce many colors commonly found in high-quality photographs.
Ambient lighting (both color and intensity) can affect color perception
substantially, as can a non-neutral background, such as a wall or carpet or even monitor bezel which is not
a neutral gray.
The viewer’s eyesight comes into play—color blindness being
the obvious issue. Even without color blindness, none of us perceive color in exactly the same way, and with
age the lenses in our eyes slowly become more yellow.
Brief explanation of RGB and Color Spaces
The most common type of digital image consists of a red value, a green value
and a blue value for each pixel. A value of 0 indicates no luminance (black) and the maximum value indicates
the brightest possible value. For 8-bit images, these values are 0 and 255. For 16-bit images, these
values are 0 and 32768 (at least according to Photoshop—16-bit in theory allows 65535). Thus, {0,0,0}
is pure black, and {255,255,255} is pure white. JPEG images are always 8-bit.
These triplets of red/green/blue values have no inherent color by
themselves. For example, the triplet (82, 89, 128} might be a medium pure blue on one particular computer
display, a cyan-blue on another display, a magenta-blue on a printer, etc.
To define which color the red/green/blue triplet describes, a frame
of reference must be used. This is known as the color space. Color spaces are relative
to a standard called CIE L*a*b,
which independently defines color in absolute scientific terms.
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