Colorspace - sRGB vs AdobeRGB

Started Jan 28, 2003 | Discussions thread
OP Chuck Gardner Forum Pro • Posts: 10,381
Re: Colorspace - sRGB vs AdobeRGB

It seems to be to be similar to the old days of computing when the
computer could only display say 16 colours out of a total palette
of 4096.

In your example the number of monitor colors depended on the number of bits. Regardless of colorspace each pixel has 8 bits per color can represent any one of 16,777,216 colors (256*256*256) its where those colors are in the human vision / CIELab gamut relative to the colors you are trying to reproduce that is important.

The colour space basically defines what actual colour each of the combinations of 24 bits maps to.

Color scientists started to map and create a model for human color perception in the late 1800s, and in 1932 the CIE ( a color standards organiziation) established the three-dimensional colorspace model and 3D measurement coordinate system which is the basis for the CIE Lab colorspace used by Photoshop as it native mode. Colorspaces are like the borders surrounding countries on a map of the world. Some political borders on maps are defined by physical contraints such as rivers and oceans, but others are completely aribitrary and usually draw by a committee with its own agenda. Colorspaces are similar. Some are defined by the capablities of specific devices such as monitors, while others are aribitrary and incapable of being reproduced completely on screen or in print.

Before computers ICC profiling color management consisted of trying to get all printing companies using similar inks (SWOP standard) and printing ink densities. Once SWOP standards were in place there was a reasonable expectation that the same CYMK dot percentages would print the same from printer-to-printer.

The first desktop color was done on Macs and a Mac monitor became the defacto standard for color matching. Radius, seeing a market for more accurate monitors developed the Pressview which had hardware calibration tools. Radius monitors had better phosphors with a wider gamut than Apple monitors and soon became the default profesional standard. The AppleRGB and ColorMatchRGB colorspaces were derived from these devices. sRGB is another colorspace which was defined by hardware. It was proposed by Microsoft and HP and defined around what a VGA monitors and CCD scanners at that time could reproduce. Monitors and CCD devices have gotten somewhat better, and as a result sRGB THEORETICALLY limits their potential.

Thus, with a wide colour space,
there is a bigger difference between each of the colours, and vise
versa with a narrow colour space.

AdobeRGB, ProPhotoRGB, WideGamutRGB and a host of others are aribitrary colorspaces which are not based on a hardware. They were developed to address the problem of converting the range of colors an RGB monitor can display into a CYMK separation for printing. It is a fact of life that CYMK pigments cannot reproduce all the cyan, purple and blues a monitor can display. You can edit the files to tweek the colors through the roof on screen, but you'll never see those colors in the printed page. The idea behind the larger gamuts is to expand a limited input gamut from the camera or scanner wide enough to cover both the RGB gamut of the input device, and the CYMK gamut of the final printed result. The only defect in this is the fact the monitor, which is relied on to adjust the color, can't accurately display the entire large working space or the CYMK output space.

would it be fair to say that if you were wanting to get the best quality prints (as opposed to monitor

display) and were taking photos of every-day things (i.e. wide variety of colours), that the adobe RGB is > a better choice than sRGB ?

If you look actual colorspace utilization as Marqulis explains it, sRGB and AdobeRGB are like two armies, each 16 million strong. The difference is that most of the sRGB soldiers are on the front line in the trenches (the part of the CIELab gamut the camera / scene photographed actually record) while many of Adobe's possible color combination are held in reserve in parts of the gamut not typically photographed.

But AdobeRGB is better in general for capture because it is a better fit to the destination CYMK output. But since you usually don't know what you'll use on the web vs printing its best to shoot in AdobeRGB all the time if you are sophisticated enough to convert the files you do use on the web to sRGB. Embeddding a profile (i.e., attaching a profile tag in the header) is different than converting. See page 99 of the PS 7 manual for an explaination of the difference

Also, do you have any comments as to the gamut of typical photo

prints (i.e. developed using photographic process) as opposed to printing on an ink-jet printer.

I haven't had an opportunity to compare them

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