Editing in RGB

margems · May 12, 2005

I am a graphic designer and photographer. I have been editing images in CMYK for over 15 years for offset printing use. Now I am shooting digitally and need to learn to edit in RGB.

I find that CMYK allows for easier editing of particular colors. In RGB it is like more of a balance. For example, if I want to reduce cyan in CMYK, I go into curves and pull the curve down. Only cyan is affected. If I want to do the same in RGB, I have to go to the red channel and pull the curve up. However, this increases the red instead of just decreasing the cyan. Any suggestions?

I would also edit just the black channel in CMYK to brighten the colors of an image. I haven't found an equivalent method in RGB. Any suggestions?

Thanks.

VG · May 12, 2005

margems said:
I am a graphic designer and photographer. I have been editing
images in CMYK for over 15 years for offset printing use. Now I am
shooting digitally and need to learn to edit in RGB.

I find that CMYK allows for easier editing of particular colors. In
RGB it is like more of a balance. For example, if I want to reduce
cyan in CMYK, I go into curves and pull the curve down. Only cyan
is affected. If I want to do the same in RGB, I have to go to the
red channel and pull the curve up. However, this increases the red
instead of just decreasing the cyan. Any suggestions?

I would also edit just the black channel in CMYK to brighten the
colors of an image. I haven't found an equivalent method in RGB.
Any suggestions?

Thanks.

margems · May 12, 2005

I use the selective color tool when needed, but find its use limited especially due to its specified and non-adjustable range of colors (i.e. red, yellow, etc.). I'm not looking to change the makeup of particular color ranges. It wouldn't help me adjust the whole range of colors (i.e. to remove a little midtone black or a cyan cast from the whole image). And you can't choose how a color is added or subtracted (i.e. no curves).

How would I use an adjustment layer for this purpose?

SBriggs · May 12, 2005

Assuming your using Photoshop, couldn't you just got to Image> Mode> CMYK color---do your editing there and then go to the same menu and convert back into RGB?

--
Sam

KTG · May 12, 2005

I sympathise with your frustration.

When I color correct for flesh tones I often make a Duplicate of the image, convert to CMYK. Make the corrections, Flatten, convert back to RGB and then paste into the image in the RGB Layers Palatte with a Color Blend Mode.

I'm sure there is some degridation in the image and the technocrats will be able to advise as to how much. For me, I have trouble seeing a problem.

k

VG · May 12, 2005

You're working with CMYK values on the fly in an RGB environment. You're not going to get the same results that you would using straight CMYK.

You look as if you need to brush up on color selections. Irregardless of CMYK or RGB or LAB, colors are integrated components, not just a specific channel. The channels are only grayscale luminous indicators.

A midtone black is gray. Curves doesn't choose how a color or added or subtracted, only the tonal range of that color.

I would suggest that you read the help file in PS on selective color. It will probably give you a much better understanding. You can do any equivalent CMYK corrections with this tool and further enhance its use by using one or more adjustment layers.
HTH,
VG

margems said:
I use the selective color tool when needed, but find its use
limited especially due to its specified and non-adjustable range of
colors (i.e. red, yellow, etc.). I'm not looking to change the
makeup of particular color ranges. It wouldn't help me adjust the
whole range of colors (i.e. to remove a little midtone black or a
cyan cast from the whole image). And you can't choose how a color
is added or subtracted (i.e. no curves).

How would I use an adjustment layer for this purpose?

margems · May 16, 2005

VG,

I just read the help file on Selective Color. And now I understand better what the colors represent. I did have a misconception there. But I still don't see how I could do equivalent CMYK corrections with this tool to the corrections I can do in curves in CMYK. With Selective Color, you can only alter a color in a straight percentage (i.e. 10% for all color values). In curves, you can vary that however you want. Generally, I pull the black curve down in the middle to brighten colors (I don't want to decrease its strength in the dark areas). You can't do this with Selective color. Or if there is a way, please tell me.

A midtone black is grey when it stands alone. When it is mixed with other colors it no longer "looks" grey, so I don't refer to it that way.

As far as "curves not choosing how a color is added or subtracted," I think we are dealing with semantics. Curves are used to control the levels (or tones) of a channel color. Using curves does, in effect, result in the addition or subtraction of the color from designated levels, depending on how you set the curve.

How can I use adjustment layers to perform this function?

margems

VG said:
You're working with CMYK values on the fly in an RGB environment.
You're not going to get the same results that you would using
straight CMYK.
You look as if you need to brush up on color selections.
Irregardless of CMYK or RGB or LAB, colors are integrated
components, not just a specific channel. The channels are only
grayscale luminous indicators.
A midtone black is gray. Curves doesn't choose how a color or added
or subtracted, only the tonal range of that color.
I would suggest that you read the help file in PS on selective
color. It will probably give you a much better understanding. You
can do any equivalent CMYK corrections with this tool and further
enhance its use by using one or more adjustment layers.
HTH,
VG

Focus Photoeditor User · Aug 17, 2010

well if you need to decrease the cyan in rgb you could just increase the red and decrease the green and blue, or if you keep the luminance constant you can just do one of the above two options.

You would have the same problem in cmyk if you had to increase or decrease a primary color (R G or B)

Kate Street · Nov 13, 2010

Actually, it is possible to adjust for flesh tones when working in RGB using CMYK.

Simply place color sampler points in the parts of the face you want to monitor. (Ex: somewhere where there isn't make up such as between the eyebrows).

When the color sample measurements appear in the INFO palette, go under the little eyedropper in each sample, press the tiny little triangle there, and select CMYK from the pop up menu. (Even if you're editing in 16 bit, choose the plain CMYK).

Now all your reading will appear in CMYK and you can adjust until you get the numbers you want.

You haven't changed modes, you're still using RGB, but you're measuring the effect of your RGB corrections in CMYK "language."
--
Kate

JulesJ · Nov 26, 2010

Have you tried Curves, then click on the RGB drop down in the Curves box, and you can then adjust each of RG&B curves independently?
Jules

--
Julesarnia on twitter

joey_B · Nov 26, 2010

Maybe it would be an eyeopener to do some research on 'layer blending modes'. I think your problem is not so much on how to alter channel information, but on how to let those alternations only affect certain aspects of a picture, like color or luminosity.

Try this for starters: Put a Curves adjustment layer on top of your original image,and tweak the R, G and B curves until you have pleasing color. Only evaluate on color, not on brightness. Your picture will probably look like crap now.

What you want with this layer, is to only apply the color info to the original. If you put the adjustment layer into 'Color' blend mode, it does just that. (you change blendmodes by clicking the dropdown box on top of the layer pallete, where it says 'normal').

Same way around, if you want to change the Luminosity info without altering the colors, you could put up a B&W adjustment layer, or a channel mixer layer (maybe in mono-mode, but that's not neccesary), and make a nice contrasty rendition. When you change the blendmode of this one to Luminosity, only this info will be sent trough to the bottom layer.

gollywop · Dec 2, 2010

you can use the HSL pane in ACR to single out Cyan. This is one of the simplest and most effective means of color adjustment I have yet found.

If you are shooting jpeg, you can still open it in ACR and gain a good deal of the same control.

--
gollywop

-----------

Search

Editing in RGB

margems

Member

VG

Senior Member

margems

Member

SBriggs

Leading Member

KTG

Leading Member

VG

Senior Member

margems

Member

Focus Photoeditor User

Senior Member

Kate Street

Senior Member

JulesJ

Forum Pro

joey_B

Senior Member

gollywop

Veteran Member

Similar threads

Keyboard shortcuts