Do Curves Throw You a Curve?
By Mark Segal
Since the appearance of Adobe Photoshop Lightroom, Adobe Photoshop CS3 Beta with Camera Raw, then CS3 with Camera Raw 4.x people have been asking about where best to implement luminosity and colour adjustments. Lively discussion of this matter occurred most recently on this website's Forum, and since before that on the Applied Color Theory List (ACTL), a Yahoo membership group run by Dan Margulis.
Mark Segal, a member of ACTL, and contributor to this website, was an early adopter of the new software products and has printed a large number of images from his raw files processed using CS3 and Camera Raw 4 in both Beta and commercial versions. Much of the recent discussions have focused on the question of using Curves and other luminosity adjustment tools in Camera Raw 4 and Photoshop.
Based on his experience using these applications, Mark found a number of positions taken in these discussions surprising, and decided to test the various arguments. He thought the results of this work sufficiently interesting to write-up and share with others. While a large amount of very good material already exists on how to use the new tools, the particular interest of this article lies in the comparisons it makes between them, and in the ways it explores the interactions between contrast and saturation and how these interactions are controlled, whether in Camera Raw or in Photoshop.
Because this essay is much longer than usual for essays on this website, containing some 34 illustrations needing particular layouts, it is made available here as a PDF download, permission granted to print and copy – with acknowledgement as appropriate. Mark has also created a Discussion Forum topic Your Curves under “Digital Image Processing”; we recommend that all discussion of this article be contained within this one topic; this helps to minimize duplication and it provides for continuity.
As most readers would know by now, Dan Margulis, a noted author on the editing of tone and color using Photoshop, has expressed considerable reservation about aspects of how the RGB composite curve performs in Photoshop, and similarly – how tone curves perform in Camera Raw. As Mark’s findings do not always confirm these positions, he has invited Dan Margulis to respond on this website and I have agreed to place online whatever Dan wishes to have published here.
In July we posted Mark Segal's essay above – Do Your Curves Throw You a Curve, and Dan Margulis was invited to respond to the article on this website. So far, Dan has not taken-up that invitation, but on his Applied Color Theory List he informed his readers that he didn't believe Mark's article covered several critical image types which in his view would be particularly challenging to edit in a raw converter without damaging the image. Mark has now responded to these concerns in a new segment of his paper, which you may download here.
Mark is a periodic contributor of essays and ideas to this website. He has been making photographs for five decades, got into digital imaging with Photoshop 6 and a film scanner in 1999, was fully digital and a "raw image" convert since 2004 and has produced thousands of inkjet prints using successive generations of Photoshop, Camera Raw and Epson professional printers.