Photoshop v.6.0 Color Settings for Linear Space Workflow

The color-management in version 6.0 is now clear, clever and very good, it enables the linear workflow without any trouble at all.

Please download the AIM profiles it is a small 2 kB zip archive that contains the following ICC profiles:

1. AIMRGB, working-space profile.
2. AIMRGBpro, widegamut working-space profile.
3. nativePC, publishing profile for the Web and for uncalibrated PC systems
4. nativeMAC publishing profile for the uncalibrated Mac systems.

It is important to note that in order to actually work with linear image data the non-linear images must be converted to the linear working-space (the middle choice in the Embedded Profile Mismatch -dialog).

If the "Use the embedded profile (instead of the working space)" -option is chosen when images are opened then the image data remains non-linear and Photoshop only performs the required compensation on-the-fly for the monitor only.

About the Dreaded Custom Profiles

All AIM profiles are saved with full colorimetric description in the filename of the ICC profiles. Therefore in the Embedded Profile Mismatch -dialog Photoshop will show not just some indeterminate ICC profile name, but the full colorimetric information of that space like shown below:

nativePC is: Trinitron primaries, D65 white-point and gamma 2.5

This way there is absolutely no fear about unknown characteristics of "custom" profiles and no particular need to distribute that working-space profile, if the profile is ever needed it can be easily created with Photoshop in a few seconds according to the displayed characteristics.

If you are using a custom RGB working-space then please do the same, it will in the future help both you as well as your partners a great deal. Just append the description of your working-space into the filename of the ICC profile when you save it.

About choosing color-spaces

The AIM RGB working space has the Trinitron primaries and the AIMRGBpro working space has the WideGamut primaries, the rationale behind theses choices are discussed below.

Every now and then we can read that a certain color-space would be "strong" with some hues and "weak" with some other hues and that some color-space would be "larger" than another color-space. Strong, weak, larger, smaller, what does this actually mean?

A color space (also known as color gamut) defines the saturation range that the particular gamut holds, most saturated colors are at the gamut edge.

When converting colors from a large gamut to a smaller gamut those colors that reside out of the receiving gamut will be mapped (e.g. clipped or scaled) in order to fit them into the smaller gamut and thus image detail can be badly damaged.

The size of the color-space relative to the available digital resolution also plays a role in choosing the color-space. The gradation in the saturation axis is more coarse with a large gamut than with a smaller gamut.

Larger and Smaller Gamuts

The below chart shows the gamut size of the most common color-spaces inside the illustration of the CIE XYZ space (drawn in form of Yxy) that is the gamut of the human vision. In addition four white-points are plotted.

This chart is somewhat crowed so it is divided below into the two charts:

Larger Gamuts

Larger color gamuts

The above chart show the larger color gamuts:

• WideGamut or 700/525/450 nm
• CIE RGB
• NTSC(1953) or CCIR 601-1
• AdobeRGB(1998)

As can be seen AdobeRGB(1998) and NTSC(1953) are technically very close to each other, in color managed workflow there are no particular benefits or disadvantages between them. They are both in the midway between a true large gamut and the CRT monitor and television gamuts.

Interestingly CIE RGB clips the most important hues (the greens) and also cyan and blue, in this respect it is not much better space than the smaller gamuts (shown below) are.

The WideGamut is largest of these four gamuts, it is widely used gamut because it approximately covers the gamut of the traditional imaging products, film and photographic paper.

Smaller Gamuts

Smaller color gamuts

These smaller gamuts are all different approaches to describe the native color-space of either the CRT monitor or the television tube.

• AppleRGB, Trinitron (CRT monitor)
• ColorMatch RGB, P22-EBU (CRT monitor)
• CCIR 709, sRGB, HDTV (Television)
• EBU-ITU, Pal-Secam, CIE_XYZitu (Television)
• SMPTE-C (Television)

As can be seen these gamuts are technically very close to each other, in color managed workflow there are no particular benefits or disadvantages between them.

However, when considering the non-color managed world (such as the the Web and uncalibrated computer systems in general) when using one of the smaller gamuts it is beneficial to choose that gamut that most accurately specifies those uncalibrated systems. For a couple of decades the Mac system has been considered to be the better, more accurate system in digital imaging and one of the main reasons for that is that the Apple RGB working space specifies such an accurate gamut, the Trinitron gamut.

Particularly there are no CRT monitors with the HDTV primaries that the sRGB specifies.

Choosing the working-space gamut

In general there is none or only a very little benefit in choosing a wider gamut than the Trinitron for the working-space gamut.

When using a wider gamut working-space gamut like AdobeRGB, CIERGB or the WideGamut the image data surely will be in that space, but Photoshop has to apply the correct color-management on-the-fly over that data that goes to the small gamut CRT.

The net effect is that the benefits of the wider gamut working-space is not visible at all on the CRT.

For the above reason Photoshop 6 now has an option in the Advanced ColorSettings: Desaturate Monitor Colors by nn %. Using this setting the finest detail from the wider gamut that potentially is there in the data can actually be seen on the small gamut of the CRT but with the reduced overall saturation if the image. About 20 percent saturation decrease of AdobeRGB or CIERGB gamut is enough to cover the extra gamut space so that the potential extra fine detail due to the larger gamut will be visible on the CRT, but with the overall 20% desaturation of all the image data. Any higher percentage will be somewhat degenerative since it will expand the simulated gamut way outside the visible spectrum.

There is benefit from a wider gamut working space only when the image output is a very wide gamut device like imagesetter (that prints to film) or a high quality dye-sub printer, with such a wide gamut output the Desaturate Monitor Colors by nn % is a very useful feature (but requires a lot of experience).

About the Blend RGB Colors Using Gamma 1.0 -option

This option is definitely a step towards the right drirection, but in version 6.0 it only covers a very small portion of the editing operations that it should cover. With linear workfow this option is redundant.