PS Curves & Prophoto Limitation?

[mcmorrison]

Hello,

In using the Prophoto colorspace, I find that making an adjustment of a single unit, say from 153 to 152, on a curve in one of the color channels makes a large, and often too large, shift in color. I am guessing this is because each of the 256 steps has to cover more ground in Prophoto than it does in A98 or sRGB.

I am using 16-bit files so the steps are available in the image, but it seems that PS curves only allows integer steps, and not fractional steps, thus limiting the fineness of adjustment that can be made in Prophoto. As a result, I have often had to revert to A98 in order to achieve the fineness I would like.

If it is possible to enter fractional values in curves, I would love to learn how. If not, I would love to see the capability in a future version of PS. It seems strange to me to have this great big colorspace, and 16-bit file capability, and then to limit the values that can be entered for adjustments to just 256 levels. . .

I also find I like the percent (with one decimal place) readouts in Lightroom, and wish for this option in PS (I realize that the info panel has a 0.000 to 1.000 readout, which is a good start). If we had this ability in PS, the curves issue would disappear?

Best Regards,

Michael Morrison

[Schewe]

In using the Prophoto colorspace, I find that making an adjustment of a single unit, say from 153 to 152, on a curve in one of the color channels makes a large, and often too large, shift in color. I am guessing this is because each of the 256 steps has to cover more ground in Prophoto than it does in A98 or sRGB.
[a href=\"index.php?act=findpost&pid=162420\"][{POST_SNAPBACK}][/a]

Do it on an Adjustment layer than set your opacity to 50% (or whatever opacity gets you to where you want to be).

[mcmorrison]

Hello Jeff,

Thanks for the suggestion. I do use the approach you describe at times, but there are other times when it is more difficult. A lot of my work is restoration and reproductions where I am doing detailed color adjustments so I have a curves adjustment layer with many components: point adjustments in each color channel and in overall tone. The times I have trouble are when I have made several adjustments and have much of the correction done, and I want to make another adjustment but need a finer control for it than the unit adjustment will give me. I could use the unit adjustment and then reduce the opacity, but then all the other adjustments—which are as desired—would be thrown off. Yes, I could, and do, use an additional adjustment layer, but it adds to the complexity and all.

Thanks again,

Michael Morrison

[Jonathan Wienke]

Set your color adjustment layers at 50% or whatever gives you fine enough control in the first place, and then you won't need to add additional ones later.

[bjanes]

Hello Jeff,

Thanks for the suggestion. I do use the approach you describe at times, but there are other times when it is more difficult. A lot of my work is restoration and reproductions where I am doing detailed color adjustments so I have a curves adjustment layer with many components: point adjustments in each color channel and in overall tone. The times I have trouble are when I have made several adjustments and have much of the correction done, and I want to make another adjustment but need a finer control for it than the unit adjustment will give me. I could use the unit adjustment and then reduce the opacity, but then all the other adjustments—which are as desired—would be thrown off. Yes, I could, and do, use an additional adjustment layer, but it adds to the complexity and all.

Thanks again,

Michael Morrison
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For restorations and reproductions do you really need ProPhotoRGB? I would think that Adobe RGB would cover the gamut of most color prints and such.

Bill

[thompsonkirk]

If you change your Curves blending mode to Luminosity, you'll fend off color shifts.  

(Bill is probably right about working space?)

Kirk

[bjanes]

If you change your Curves blending mode to Luminosity, you'll fend off color shifts. 

(Bill is probably right about working space?)

Kirk
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Or if you do need a bit more gamut, you could use [a href=\"http://brucelindbloom.com/]Bruce Lindbloom's[/url] Beta Color space, which covers  the color film gamut.

[Jonathan Wienke]

If you change your Curves blending mode to Luminosity, you'll fend off color shifts.

That would kinda defeat the purpose of using the curves for color correction, though...

[thompsonkirk]

Indeed.  Your mileage/workflow may vary, but in ProPhoto my habit is to control contrast, make a Luminosity Curve; to control color, make a Normal Curve (or to stay within gamut, reduce the saturation in a selected color range/area).  I'd avoid a Normal Curve in ProPhoto to control contrast, because you can get such overbearing outcomes in prints.  Especially Canon & Leica yellows (I don't know about files from other systems).  

K

[mcmorrison]

Hello,

Thanks for all the input. I hadn't realized that Bruce's BetaRGB was tuned so closely to film. It makes great sense for working with restorations! Yes, Prophoto does seem like overkill for restorations anyway. I do use a luminosity-only curve separate from color sometimes, and at other times combine them. I seem to get good results from both with different images. Perhaps with more experience I'll settle on one or the other more generally?

While it seems to be an issue that only Adobe can solve, I still wonder why the curves dialog is limited to integer values when the rest of PS is so accommodating of big color spaces? Perhaps in the next version?

Many thanks!

Michael Morrison