Re: The group's techniques, 2

Thomas Hurd,MD


Thank you so much for managing this competition. For me, this was the very first time I presented a file to anyone in CMYK.
But it was great fun and challenging to come up with a file, even though I had no idea what to expect, just that I was trying to head as close as possible to the original impossible RGB colors as I could manage while stuck in CMYK.
Looking at all the entrants before the comments were posted, I agreed with what you, and many others, concluded. There were a lot of images that were close to one another and pretty good.
On Saturday, I just kept looking back and forth, saying “contrast, color” over and over. And I was most anxious to read everyone’s comments. And they didn’t disappoint. 48 hours later I know a lot more about color correction in CMYK. What happens when you add C, why do you add C, where does M100Y100 show up, etc. 
Before I run on (and on...), I want to say that 209 was my favorite, because I liked the color of red and there was good detail maintained along the yellow stripe. 
And for most of the last 2 days, I thought thought red was a bunch of nearly equal M and Y. Then I decided it was a little more M than Y, but C < 6. Today I think maybe it’s c16m80y70b??
It’s probably even tougher to look at a monitor for an hour, with no other colors around except a white background and a yellow bag, not enough to even give me a good excuse to bring up simultaneous color contrast. 
And now I just want to know: what is red?

Tom Hurd

On May 18, 2020, at 12:05 PM, Dan Margulis via <dmargulis@...> wrote:

When faced with multiple problems in the same image it pays to plan out the approach before striking out in all directions at once. Here, how much work should be done in RGB? How much in RGB? In CMYK?

Before seeing the image, I would have bet that, since we have a somewhat RGB-centric group, that’s where the fun might be taking place, whereas since I have more CMYK experience I might be doing more work there. It didn’t turn out that way.

Five of us determined from the get-go that we were going to make at least two versions of the image and then combine them. In four of these cases one of the versions had been desaturated, either slightly or completely. Unless I missed it in the notes, I was the only one who used Hue/Saturation limited to Reds, so as not to disturb the yellows.

Only three people applied RGB curves and only two of them were trying to affect overall color; notably in #209 there was a desire for a warmer, more orange red.

Only two people tried channel operations within RGB. Both wanted to boost contrast in the red channel, a good idea since that’s the one most responsible for shape when the interest object is bright red. One person accomplished this by blending the green channel into the red; the other by multiplying the red into itself. Neither version made it to our list of favorites.

When the image starts out this colorful, LAB doesn’t have many attractions, so few people used it. What’s going on? If people aren’t going to use much RGB, or much LAB, surely they don’t just convert into CMYK and get the disaster that is the default, #200. Or do they?

A CMYK fact of life: the lighter the desired color, the worse the possible gamut mismatch. If we were doing pink flowers the problem would be much more severe, and we’d see a lot more variation in the quality of our corrections.

Why? Since we can’t lay down solid magenta ink without creating a red rather than a pink flower, we rely on the paper itself to create lightness. This is unfortunate, since paper is not absolutely white; it reflects a certain amount of green and of blue light, both of which are red-killers.

The response of the experienced CMYK practitioner is that adding more ink allows a more colorful result, and that it is better to have the flower too dark than too gray. But exactly how dark to make it is a tough judgment call

When an RGB file is full of brilliant colors that CMYK can’t hold, it’s critically important that we get them as bright as we possibly can. Here’s my favorite trick, which I illustrated in CC2E with a picture of brightly colored cycles.

1.   Assuming approximately correct colors in RGB, make two copies and move them into LAB.

2.   Copy 1: desaturate it slightly until you are sure that nothing will be lost by moving it into CMYK.

3.   Copy 2: use Color Boost or similar action to produce colors so bright that you absolutely will lose a lot of detail on conversion.

4.   Place Copy 2 as a layer on top of Copy 1.

5.   Change layer mode to Color. No apparent change from Normal mode, since the L channels of the two layers are identical.

6.   Move into CMYK without flattening. Surprise! Suddenly the detail returns, because Color mode in CMYK tries to retain the structure of the black channel, which is responsible for a lot of the detail.

7.   Add another copy of Copy 2 to the stack and set mode to Normal, massacring detail once again.

8.   Reduce its opacity to the maximum you can stand. The higher the opacity, the more colorful, but also the more detail is sacrificed.

So by habit, I used this elegant procedure and produced a suboptimal image. Why? Because with a lot of colors in play, of various darknesses, it’s really hard to know whether we’ve gotten all the color possible. Not true in this Carnival image. Getting maximum color is a piece of cake, pretty much everybody did it. The robe is dark enough that if we push its maximum color to 0c100m100y0k nobody will care. It’s easy to do with CMYK curves. No need for all these gyrations when we can just attack the detail in the CMYK channels directly.

Three other people followed the above procedure. Meanwhile, eight people took the more direct approach of converting into CMYK followed by blends into at least the cyan and often the magenta channel. Of these, one (#210) used my LAB procedure as well. The other seven, AFAIK, just glommed the file into the terrible #200 default and then fixed it. One of the eight blenders took his blend source from within CMYK but the other eight used RGB channels as the source: at least the red into the cyan, and often the green into the magenta. That is a highly sophisticated technique that I wouldn’t have expected to be so widespread. It appeared in many of the versions we listed as favorites, including #203, #210, #211, and #214.

Some of these people also applied curves to the RGB channels to add contrast before blending with them. Particular kudos to Rick Gordon, who thought to convert the Adobe RGB file to ProPhoto RGB before using its channels as a source. ProPhoto has a much wider gamut and isn’t impressed by how red this image is. It therefore shows subtler detail in its channels than Adobe RGB does.

Beyond that there was some variation, but few surprises. Two of us experimented with different rendering intents on conversion. One person created an entire layer of 0c100m100y0k and used it, masked, for various purposes. Six people used CMYK curves, sometimes through a network of masks. Two used Selective Color to enhance the shadows.

All in all, an excellent group effort.













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