Perceptually Uniform and Error Free Saturation Effect using Channel Mixer

A linear RGB working-space makes it possible to use the Channel Mixer operation of Photoshop for various editing operation in the perceptually uniform CIE XYZ color space, in this demonstration saturation enhancement is demonstrated and compared with the built-in Hue/Saturation -command of photoshop in two working-spaces, the linear AIMRGBpro and the non-linear AdobeRGB(1998).

Accurate ChannelMixer command files for the AIMRGBpro working space were created using the CIE photopic colorimetry in Microsoft Excel, ranging from saturation of -99% to +100% (200 files all together, best to save them into their own directory for easy usage). The method for perceptually uniform saturation adjustment is to scale the x,y chromaticity points of the RGB codes in relation to the whitepoint x,y location by a chosen constant. Mathematically this reduces to scaling of the gamut of the linear RGB space in relation to the whitepoint x,y location, illustrated on the right.

Gamut scaling is often considered to be an inferior method as it can cause saturation clipping (out-of-gamut colors) so the demonstration image (a 16-bit/color photo in AdobeRGB(1998) space with the profile embedded) is a colorimetricly accurate Kodak Q-60 Color Input Target, such a target should show gamut clipping problems as well as many other errors more clearly than an everyday photo.
 

AIMRGBpro workflow with ChannelMixer saturation
 

AIMRGBpro workflow with Photoshop built-in Hue/saturation command
 

AdobeRGB(1998) workflow with Photoshop built-in Hue/saturation command
 

1. Open the original by preserving the embedded profile.
2. Convert to AIMRGBpro profile.
3. Apply Saturation increase with AIMRGBpro +033.cha using the ChannelMixer.
4. Apply USM at A=150, R=0.5, T=0.
5. Convert to nativePC profile for Web publishing.
6. Convert to 8-bit/c mode.
7. Save as JPEG with Quality 12.

1. Open the original by preserving the embedded profile.
2. Convert to AIMRGBpro profile.
3. Apply Saturation increase by +30 using Photoshop Hue/Saturation command.
4. Apply USM at A=150, R=0.5, T=0.
5. Convert to nativePC profile for Web publishing.
6. Convert to 8-bit/c mode.
7. Save as JPEG with Quality 12.

1. Open the original by preserving the embedded profile.
2. Apply Saturation increase by +30 using Photoshop Hue/Saturation command.
3. Apply USM at A=150, R=0.5, T=0.
4. Convert to nativePC profile for Web publishing.
5. Convert to 8-bit/c mode.
6. Save as JPEG with Quality 12.

Slowly toggle between original (option 1) and one of the edited version at a time and evaluate what workflow gives perceptually most uniform effect, without major damages to the image.

Additional reading suggestions:

The new Workflow Comparison Gallery, USM, Gaussian Blur and Saturaration so far.