Dan Margulis approach to color correction in PS and Affinity Photo

[LenC]

This is long – my questions start in the third big paragraph.

After spending a couple of years trying to learn how to improve my photos in AP, I think I see some light along the difficult path in the form of Dan Margulis’s Professional Photoshop (5th ed.) and his other books.* His approach to color correction involves understanding human perception, color spaces, image processing algorithms, and means of rendering images in print and on screen. It should translate well to other image processing programs such as AP. I find his approach so persuasive that if I had the time I would get PS to pursue it. Right now, I need some help applying some basics to AP.

Two fundamental tools that Margulis discusses at length are curves and channel mixing. He gives many examples of color correction with curves in RGB, CMYK, and LAB that are easy to learn from. A minor issue is that he displays curves with dark on the right, whereas AP only shows dark on the left. These can be compared by mentally or physically rotating the curves 180 degrees. PS has a one-click control to flip them.

Channel mixing does not translate so well. The fundamental Margulis maneuver in PS is to choose a channel in RGB (e.g., the most contrasty), use the Apply Image command to create a BW layer from that channel above the image layer, and then use Luminosity blend mode to increase the contrast. Creating this layer from existing channels seems to involve only a couple of steps. But this does not work in AP, which seems to be set up only to blend two layers, not create a separate one. Also I can select a source layer but I don’t understand how I select the destination (the pixel layer I created to receive the channel). This has got to be trivial but reading Apply Image help does not seem to help. “Apply” button grays and becomes active in a way I have not figured out. Also it appears that the equations operate in only one color space, while PS allows blending cyan with RGB. Can someone help me see if my task can be done in AP? It’s got to be simple.

And why are the Composite channels more functional (show, edit) than those of the other layers?

 

Although it goes beyond my immediate inquiry, it could be an important influence on the evolution of AP if, among those AP and PS users who are aware of Margulis’s work, there is enough interest to justify developing better user interface elements. (I already have a couple of ideas.) Many advanced retouchers are very enthusiastic about his writing (see reviews of his books on Amazon). Margulis and co-workers have also automated some of his more complex approaches using PS script actions, available through a freely distributed panel. This appears considerably more capable than the AP macros.

 

* Professional Photoshop: The Classic Guide to Color Correction (5th ed., 2006); Photoshop LAB Color The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace (2nd ed., 2015); Modern Photoshop Color Workflow: The Quartertone Quandary, the PPW, and Other Ideas for Speedy Image Enhancement (2013).  Somewhat pricey, but good value. I bought second-hand copies of the first book and the first edition of the second. One lacked the CD. I have not read the third, but there is plentiful information available online, including videos for most chapters.

[blackxacto]

I would like to see what Affinity can do with channels. Is there a video tutorial anywhere?

[firstdefence]

For anyone that runs Photoshop as well as Affinity Photo here is a link to his Picture Postcard Workflow Panel

See the link for Videos in my sig, and scroll down to the Channels section... or use find (Press ⌘ + F and type 'channel')

 

[toltec]

3 hours ago, blackxacto said:

I would like to see what Affinity can do with channels. Is there a video tutorial anywhere?

 

Here is one to start with. There are others (I think) so I’m sure someone will post them.

 

 

 

[firstdefence]

Hey, I'm someone lol!

[toltec]

OK someone else 

 

[firstdefence]

@LenC Wouldn't the Channel Mixer Adjustments Filter work for you?

I'm just reading up on Dan to get a fast forward on your questions.

[LenC]

Thanks, firstdefence and toltec, for your suggestions. I will review these tutorials and if they answer my questions I will post something more specific in this thread (may take a while). If @MEB is about, he answered a channels question a while back quite incisively.

Sorry for slow reply - I had notification on and thought I would get emails, but I had not realized there were so many options.

[LenC]

The Apply Image procedure that I am trying to reproduce in AP is described for PS in a video labeled "Chapter 04. The Apply Image Command" on the page

http://www.moderncolorworkflow.com/private-resources

and described in detail in Professional Photoshop (5th ed.) in Chapter 10, "Every File Has Ten Channels."

 

 

[LenC]

If anyone is still interested, or may come on the topic in the future, the answer to the question of how to create a gray-scale pixel layer from the current RGB image in order to blend it using some special blend mode, such as Luminosity, is as follows.

Open an RGB image. Choose the channel to convert from the Composite channels in the Channels panel (e.g., Composite Red). These have the eye and pencil icons on the right.

Right click on the channel of the same color among the channels listed with the original image's name (e.g., Background Red). Choose Create Grayscale Layer. The new layer will appear above the original layer.

Adjust the blend mode.

 

Incidentally, the preceding post's reference to PP5 should include Chapter 8 as well as 10.