Interchannel Color Correction

[Guest]

Although this is a very old technique and this sample chapter online is 18 years old I wonder if interchannel color correcting with the Apply Image command on channels is obsolate or it's worthwhile going deeper into it anyway.

"Rather than working with Adjustment Layers, Chris does all his color correction through the Apply Image command. The Apply Image command allows you to mix varying amounts of different channels with each other with precise control"

I understand that the Fade command also provides a way to have blend modes on channels (copy/paste/fade). Yet, Apply Image has masks and add/subtract modes. Channels (RGB/CMYK) are in a way similar to plates in prepress so maybe those who started in the industry decades ago (half-tone etching?) are more familiar with this technique. I think interchannel color correction plus density masks are still powerfull tools.

Thanks

[skoobey]

Re: Interchannel Color Correction

We have channel mixer adjustment layer now

[Guest]

Re: Interchannel Color Correction

But is it really the same?

[skoobey]

Re: Interchannel Color Correction

Well, depending on what you want to do yes and no. It replaces information from one channel to the other, but it lacks blending modes of the apply image. I must admit that I don't use that kind of color-adjustment.

Density masks I use.

[Sabrina81]

Re: Interchannel Color Correction

The article you linked to is all about working with CMYK files. Very few people do that sort of work.

[Shoku]

Re: Interchannel Color Correction

The two channel mixing tools, Apply Image and Calculations, can be useful in extreme circumstances. As when one channel is way too light or overly dark to cause an extreme color cast.

A simple move without masking in Apply Image can reduce a blue cast in shadows like the image below.

Both tools can be used in CMYK and I have found Calculations to be very effective in CMYK to reduce casts and improve the black channel.

However, I use them very rarely as there are other ways to accomplish most of what they can do, and we get fewer bad images these days that would benefit from these tools.

[Guest]

Re: Interchannel Color Correction

A reminder of the blending procedure: the channel that I plan to blend into must be displayed on screen. Then, I choose any other channel as the source in the Apply Image dialog box. Then, It's about % opacity. In normal blending if I pick 20% opacity that would create a channel that is a mathematical blend where each pixel being 80% of the older channel plus 20% of the blending channel. Total amount is 100%. What if I want to go over 100% (as it is possible in Channel Mixer), will "add" allow that?

Thanks

[Shoku]

Re: Interchannel Color Correction

A reminder of the blending procedure: the channel that I plan to blend into must be displayed on screen. Then, I choose any other channel as the source in the Apply Image dialog box. Then, It's about % opacity. In normal blending if I pick 20% opacity that would create a channel that is a mathematical blend where each pixel being 80% of the older channel plus 20% of the blending channel. Total amount is 100%. What if I want to go over 100% (as it is possible in Channel Mixer), will "add" allow that?

The Blend modes act like they do for any layer adjustment. To blend a channel to another channel via Apply Image more than 100% is not possible. The effect can change based on blend mode, but usually the more successful Apply Image adjustments are subtle. However, you could use Apply image multiple times to the same channel using Add, but the result will not be the same as the result from Channel Mixer.

You could also use Calculations, where you can select specific channels to blend.

Whatever you use you will need to experiment and settle on adjustments that work best for you.

[klev]

Re: Interchannel Color Correction

Add blending adds values together.

[r3,g3,b3] = [r1,g1,b1] + [r2,g2,b2]

It clamps anything that hits 255. You can see this by using add blending over a layer filled with white. It has nothing to do with the percentages indicated by channel mixer. You can of course apply things multiple times, but I prefer to keep things as simple as possible.

[Sabrina81]

Re: Interchannel Color Correction

You seem to be trying to find a difficult way to accomplish a relatively simple result. Why dig up an antiquated method from 18 years ago when Photoshop provides greatly improved tools that do the same thing?

[skoobey]

Re: Interchannel Color Correction

You seem to be trying to find a difficult way to accomplish a relatively simple result. Why dig up an antiquated method from 18 years ago when Photoshop provides greatly improved tools that do the same thing?

Precisely.

[Guest]

Re: Interchannel Color Correction

Why dig up an antiquated method from 18 years ago when Photoshop provides greatly improved tools that do the same thing?

I understand that and the channel mixer makes all of this easier. Yet, if I want to blend other channels (L* etc..) the antiquated method will still do it.

On a seperate note; the method explanation I originally postes sounds misleading:

"he blended 25% of the cyan channel into the magenta channel. Interestingly enough, he used the magenta channel to mask itself out by checking Mask and Invert."

In fact, the result is 25% of the cyan channel into the magenta, yellow and black channel (he blends into the cmyk composite).

How one would achieve that with the channel mixer?

Thanks

[klev]

Re: Interchannel Color Correction

In fact, the result is 25% of the cyan channel into the magenta, yellow and black channel (he blends into the cmyk composite).

How one would achieve that with the channel mixer?

Thanks

That's trivial with channel mixer. Just set them appropriately. Whatever you do, it has to be equivalent to some sequence of mixing operations, and you can work through it in a minute or two.

The thing about blending the L channel is the worst idea anyone has ever posted on here, because it doesn't follow a scale similar to any other channel, so it makes no (mathematical) sense to take a linear combination of it and something else.

[Sabrina81]

Re: Interchannel Color Correction

I understand that and the channel mixer makes all of this easier. Yet, if I want to blend other channels (L* etc..) the antiquated method will still do it.

On a seperate note; the method explanation I originally postes sounds misleading:

"he blended 25% of the cyan channel into the magenta channel. Interestingly enough, he used the magenta channel to mask itself out by checking Mask and Invert."

In fact, the result is 25% of the cyan channel into the magenta, yellow and black channel (he blends into the cmyk composite).

How one would achieve that with the channel mixer?

Thanks

Blah blah blah blah blah. Pursue these geeky nits if you must.

I'm. Not. Interested.

[skoobey]

Re: Interchannel Color Correction

Blah blah blah blah blah. Pursue these geeky nits if you must.

I'm. Not. Interested.

Exactly. Doing actual work is far more entertaining. What is the point of experimenting with something that can't possibly be of any use?