Ed -- I agree with Eric on this one. Dan Margulis has done a ton of hard work to contribute many great things to the imaging world... even if just by being a strongly opinionated contrarian to force others to be really sharp.
But if we wanted to have a battle of dueling experts we could get into all of the equally experienced & credentialed people like Andrew Rodney and Bruce Fraser who put out very different approaches on many important matters. It doesn't make DM wrong about everything, but the fact that some of his ideas are good doesn't make him right about everything either. I use experts to identify areas of workflow that I may want to pay attention to. But at the end of the day three things make more impact to me than just the experts' face-value statements:
- - Trying to sort out the underlying theory of why things work the way they do, rather than just following an expert's blanket statement such as "always do X" or "never do Y" just because I the expert claim it's mindless to do otherwise
- Pragmatic experience of working with a technique for my purposes, and weighing the benefits vs. the problems
- How well the technique meshes with everything else I'm doing in my workflow
Eric has mentioned some of the short-comings of parts of DM's base level technique. In your selected quote, he claims that wide(r) gamut images don't exist, or grudgingly admits that even if one can be found it's a rare case. Well as I showed in this thread, I found one myself in the first test case I looked at and suspect my library contains many more. So they can't be all that rare. Further his use of polarizing terms like "mindless extremes" and "ham-handed", seems to me to have moved beyond simply having strong opinions based on facts, to a level of religious fervor. I don't doubt that he has good reasons for what he says, but some of his points contradict my direct experience and he seems to lace his factual info with some big dollops of rhetoric. It makes me have to work harder to mine the useful parts of his approach. This is annoying... but I digress.
My goal is to understand things, test them, and use them if pragmatic & beneficial. Part of what I wanted to accomplish in commenting in this thread has not been to be argumentative, "right", or convince people to use a technique that they don't understand or need.
Rather it has been to debunk some of the simplistic anti-ProPhoto RGB sentiment that has been publicized out there and demonstrate why using it could be beneficial for some people, based on real cases and a real way to test images of one's own...
Greg -- I'm sure you know, tonal separation in itself is not a problem, as long as within the context of a given color space the colors look and reproduce equivalently. The human eye does pick out relative differences more easily than absolute differences... color shifts for any reason would be undesirable. As I've said all along we have to be aware of the trade-offs in working with something like ProPhoto RGB and not be (to borrow DM's term) "ham-handed" in applying it. The real problem would be applying a set of image adjustments that distort the color in undesirable ways. This can be just as easily done in sRGB, Adobe RGB or any other by a person who is heavy-handed or imprecise in their post-processing work.
So it comes back to knowing how to use the technique appropriately according to its strengths & weaknesses. If the choice is clip saturated colors or risk shifted colors, I'll take the latter and learn how to make more precise corrections. For example one simple thing I adopted awhile ago is making most tonal adjustments on separate layers with the blending mode set to luminosity to hold color shifts at bay. It works equally well in any color space but is potentially more important with ProPhoto RGB images because of the wide range of tonal values and saturated (even artificial) colors... in essence these factors give people more rope with which to hang themselves, so care must be taken. But really that level of care should be taken in a smaller color space anyway... distorted color is distorted color whether the gamut is wide or narrow, or the tone values are dense or spaced out.
As long as the colors are not distorted, any image in Adobe RGB or ProPhoto RGB is going to be converted back to another (usually smaller) color space for viewing onscreen or printing, anyway. So the wider tonal spacing of ProPhoto RGB is not the final story and we also have to pay attention to how it compresses back down for output.
Your suggestion of matching the color space to the image is no bad thing. If I had a complete level of discipline right now
I'd be using Joseph Holmes' series of 5 DCAM color spaces, which I've mentioned before. But there are some pragmatic reasons I don't (aside from being lazy
), one of which is that I can't select any of them as the output of ACR for RAW conversion. The other of which is I haven't put into my workflow the critical step of evaluating an image's real gamut to know how large or small a color space to use for it. I do know that I have many images where color clipping may have occurred in the past, so right now I'm choosing to err on the side of caution using ProPhoto RGB as the default, and don't seem to be suffering for having done so.
Be that as it may, we still have the fact that imaging applications like ACR, Lightroom, Lightzone, etc. are wired internally for ProPhoto RGB no matter what color space you convert an image file into. HDR applications, which I'm working with, introduce a further challenge by going to a 32-bit tonal spectrum as the "working space" (although HDR image formats are not really color managed yet in the same way). So we are going to have to come to grips with working in big spaces with high resolution for tones, and gamuts involving saturated colors. IMO it's eminently doable, for those who want that extra bit of kick.
As a side note I'd be interested to see a real test case of the scenario you outlined here with a blue sky gradient for example. I don't know if you have time to create one. I may have a go at it if time permits in the next couple of days...