Saturation-depending gradation curve, what is it all about?

[Kabambatron]

Dear all,

While using several different attempts to find information about a color operation that puzzles me, I stumbled upon this forum. I would like to kindly ask you about your opinion.

Heidelberg once produced high end scanners that where run by their own software called NewColor. This software not only allows to scan and alter images in RGB but also in a form of LAB color space.

Besides different tools to alter color, there is a brightness gradation curve tool with two options called global and neutral.

I already verified that setting the option to global allows for a simple adjustment of the L curve. I could reproduce the effect in Photoshop using a similar shaped L curve adjustment.

The option neutral, however, still amazes me. I played around with it while using IT8 color targets as sample images. The program seems to apply the set curve with maximum intensity to neutral tones and reduced the intensity with increasing saturation. Maximum saturated colors are not influenced at all while gray scale wedges are influenced similar to the way they are when using the "global" setting. This function is in the manual only described as a tool to reduced grayness.

I don't know if the intensity of luminance adjustment is increased linear to the change in saturation or if another function is applied. I could not reproduce it in Photoshop yet. However, it seems to increase the contrast in a unique way I have not seen before and many images benefit from it.

Have you hear about it before and do you know more about it? Is there a traditional Photoshop or Image Magick procedure with the same result that I do not know of yet?

Best regards,
Christian

[xpatUSA]

Dear all,

While using several different attempts to find information about a color operation that puzzles me, I stumbled upon this forum. I would like to kindly ask you about your opinion.
The option neutral, however, still amazes me. I played around with it while using IT8 color targets as sample images. The program seems to apply the set curve with maximum intensity to neutral tones and reduced the intensity with increasing saturation. Maximum saturated colors are not influenced at all while gray scale wedges are influenced similar to the way they are when using the "global" setting. This function is in the manual only described as a tool to reduced grayness.

Is there a traditional Photoshop or Image Magick procedure with the same result that I do not know of yet?

Best regards,
Christian

Have you looked at RawTherapee? It has a tool called the "HSV Equalizer" (Hue-Saturation-Value). The tool is by no means intuitive but a curve of sorts can be applied to Saturation independently of Hue and Value.

Also, under Lab adjustments it has 6 curves where anything can be re-plotted to anything, voila:



My curve for chroma-in to chrome-out is way OTT, just to show what can be done.

The victim was a faux tinted IR shot with very little saturation:



RawTherapee's native working space is ProPhoto and it uses 16-bit floating point so you can get pretty drastic and get away with it

[Kabambatron]

Thanks Ted for the heads up. I used RT at wpork when we did not have Light room. The HSV approach is the most promising, but Photoshop does not offer this color mode. Otherwise I would have used an appropriate S-curve on the Value channel and used the inversed saturation channel for masking the the curve, to make it saturation depending. I will have a look at raw therapee in this respect.

[bambleweeney]

Photoshop does (or did) have an HSB/HSL filter that disappeared in CS4 apparently. It is pretty useful and can still be downloaded from the Adobe web site (Google Adobe HSL filter which should get a link)
I use it to create a saturation mask for the Hue/Saturation adjustment layer allowing me to affect saturation depending on the ammount of saturation in various areas of the image.

[jcuknz]

I have found an HSL menu page in PSPX6 in the Adjust/Hue and Saturation menu which I have never found to be much use for anything realistic as opposed to manipulation/distortion etc but thanks for the head-up ... with only the left part of the image selected I managed this
An IR shot of the creek at Canon City CO.[?]



Maybe I should look at RT