View Full Version : Replacing a Color Channel


Doug Nelson
06-03-2002, 12:01 PM
View here (http://www.retouchpro.com/tutorials/index.php?m=show&id=23)

Another great tutorial from Jakaleena. This one tells how to replace a damaged or otherwise ailing color channel with a whole new one.

DJ Dubovsky
06-03-2002, 12:51 PM
Oh cool. One of my terrible photos made it's debut in a tutorial. Yup that was a nasty one. Great tutorial again Jak. You're getting to be quite the pro at this tutorial business. Hey, you do a few more and you could be the next Katrin publishing her own How to book. :) Of course if you keep popping them up on this site no one will buy the book. :D Just kidding
DJ

Ed_L
06-03-2002, 01:28 PM
That one will be very useful for a lot of people. I'm beginning to wonder just how many gifts you're going for! :D

Ed

Jakaleena
06-03-2002, 01:46 PM
Originally posted by Ed_L
That one will be very useful for a lot of people. I'm beginning to wonder just how many gifts you're going for! :D

Ed

Now that people have started tossing presents at me, I'm figuring these tuts are like the old S&H Green stamps. I'm building them up to exchange for a LAWN TRACTOR! (John Deere please... :) )

:tongue:

Jakaleena
06-03-2002, 01:53 PM
Originally posted by DJ Dubovsky
you could be the next Katrin publishing her own How to book. :)
DJ


Actually, that's not a far cry from reality. My plan is to make a pitch to the local adult education facility to start a class on restoring old photos (they already offer computer classes). I'm just trying to get a lesson plan together and some materials to work with before I approach them with the idea. When Doug asked me to write some tuts, it helped give me a nudge toward preparing my prospective class materials...

DJ Dubovsky
06-03-2002, 04:35 PM
Alright!!! Excellent idea and a good way to go about it. I think you will be great at it Jak. Let us know how your venture turns out. Sounds like a real good plan.
DJ

winwintoo
06-06-2002, 10:05 AM
From turorial
"1. Make a duplicate of your image. Select Image > Duplicate from the pull down menu, or right click on the blue bar at the top of your image and select Duplicate. In this image that I am working on, the blue channel looks pretty guilty, so out it goes..."

Just a heads up: Macs don't have a blue bar at the top of the image nor to Macs have a right mouse button (unless they're using and aftermarket mouse) Even if there is a right mouse button present, clicking it doesn't bring up the choice of duplicating the image.

In many instances, clicking the "control" key in combination with a mouse click will mimic the Windows right mouse click, but not in this case.

The only way I can find to duplicate an image on a Mac is with the Image>Duplicate menu option.

In addition, to duplicate an image and automatically append the word "copy" to its filename, hold down Alt (Windows) or Option (Mac) when you choose Image>Duplicate.

take care,
Margaret

Jakaleena
06-06-2002, 10:17 AM
Thanks for clarifying that, Margaret. It's been a long time since I worked on a Mac, so I'm extremely poorly versed in Mac menu commands.

I'm glad you're looking out for those Mac differences!

winwintoo
06-06-2002, 10:32 AM
I should pay more attention, but I've used a Mac as long as there have been Macs, and also had to use a Windows machine at work, so I've gotten used to translating. Doug mentioned a while ago that there doesn't seem to be many Mac people participating and I got to thinking that maybe if I contributed more, it might inspire others to contribute too.

I still enjoy your tutorials and I admire your concise prose (I tend to trip over my own hands whenever it try to explain anything LOL)

Please keep the tuts coming and I'd be happy to translate any differences for you,

Thanks again for the good work,
Margaret

Doug Nelson
06-06-2002, 10:37 AM
Margaret:

How about some Mac tutorials? :)

Jakaleena
06-06-2002, 10:39 AM
If you are aware of any sort of translation lists or anything, I'd really be interested in having that.

Kind of like the PC-Mac version of an English/Spanish dictionary... :lol:

fugitive
06-06-2002, 10:46 AM
I've had an idea for a while, bringing PCs to people in Retirement Homes. It seems they spend so much time doing nothing, not using there minds, and I'm sure some of them still have one.
People of a certain age or mind set have had no exposure to puters and don't know what lies in wait in that funny looking box. The graphics instruction Jak mentions would be perfect for these folks, after all, who has more old photos. just an idea, perhaps one could get a grant to empliment such a program. People are living longer and bordom is worse than death, to me at least.
greg

winwintoo
06-06-2002, 10:56 AM
Hi Jak and Doug - I don't have much to offer in the way of tutorials (I'm still fumbling around) but I will go through the tips and tuts that are already posted and work on a list of "translations".

I'm off to take Grandma for her day at the casino, but I'll work on it when I get back.

Take care,
Margaret

Jakaleena
06-06-2002, 11:13 AM
Greg,

That is an EXCELLENT suggestion!

We've got a discussion about that idea going over HERE (http://www.retouchpro.com/forums/showthread.php?s=&threadid=2740&perpage=15&pagenumber=1) in the Work/Jobs section.

Maybe, you could post that idea over there and join in with us...

Doriedee
06-06-2002, 12:41 PM
Another one of those novice questions for you..
This tutorial was very easy to follow, but my question is, how do you determine that you need to replace the channel in the first place... Just cause it looks the worst or is there a rule ??


Thanks
Donna S

Jakaleena
06-06-2002, 01:17 PM
I usually look at the channels first thing.

If I see that most (or a lot) of the damage I'm going to try and repair resides mainly in one channel instead of being spread throuought all three of them, then I replace the channel.

A good example is in retouching challenge #3 - lost weekend. If you download that one and look at each channel, the red channel contains a huge amount of damage that isn't apparent in the green and blue ones.

In less than 2 minutes, by replacing the channel and making a curves adjustment, I came up with this difference - a much better starting point for the job...

Stephen M
06-07-2002, 03:40 AM
Some related PDF links of interest:

http://www.ledet.com/margulis/Poetry.pdf

http://www.ledet.com/margulis/Numbers.pdf

Aimed at colour correction - but the mechanics of channel blends/swaps using channel mixer/calculations/apply image are similar.

There is a whole book devoted to these types of Channel Operations (CHOPs) - which I first found in Kai's Power Tips all those years ago...do a search for Photoshop Channel CHOPS if you would like to find out more.

Another eye opener is LAB based retouching for severe restoration - splitting colour from tone can be CRITICAL and LAB does this while RGB/CMYK do not.

http://www.ledet.com/margulis/LABCorrection.pdf

Regards,

Stephen Marsh.

rosieb
03-13-2003, 11:20 AM
I can't figure out what I'm doing wrong, but on the picture I'm working on, the blue channel is the problem, too. I thought I could just follow all your directions (which are very clearly written and easy to follow), but there doesn't seem to be any change once I've finished. It still looks as bad as it did before.
What do you think I'm doing wrong?
I really have learned a lot from reading the tuts here, by the way.
Thanks!
Rosie B.:confused:

Jakaleena
03-14-2003, 05:18 AM
It's really difficult to know why it's not working for you without actually seeing what you're doing. Most of the time, when replacing the channels doesn't work, there's a small part of the procedure that's getting missed.

If you'll post a sample of the image you're working on, I can try switching the channels here and see if I have any sort of problem with it.

EdwardA
06-11-2003, 03:47 PM
Hi,

I'm glad I found this place. I have had Katrin's book for several months and this is one of a couple of examples I keep messing up on.

Using PS7 when I move the lighness layer to the blue channel I end up with an Alpha 1 and not a replaced blue channel. I noticed in the example here that (select all ) is added. I used that and when I move the layer I get a red cast onthe photo with an additional lightness layer.

The way I read both examples I should end up with only 3 channels red,green and blue.

Any ideas what I'm doing wrong?

More mess ups to follow.

thanks
Edward A

CJ Swartz
06-11-2003, 08:24 PM
The way I read both examples I should end up with only 3 channels red,green and blue.

Yes, that's the way it works. The method I use is a bit different from Jak's, and Katrin Eismann's, and I don't remember where I read it. I click on the Blue channel in the original, and the Lightness channel in the dupe to select those channels -- just as the tutorials state. Then I do a Select All (Ctrl-A) of the Lightness channel and a Copy (Ctrl-C) of that channel. Then I go to the Blue channel of the original image and do a Paste command (Ctrl-V). The Lightness channel is pasted in the place of the Blue channel.
NOTE: I typed it wrong, Chuck caught my error -- thanks to him for getting me to correct it. ;)

I know the steps in the tutorials (Jak's and Katrin's) must work, but I ended up with the new Alpha channel instead of a replaced Blue channel -- just like you. So I do it this way. :)

This may often result in a color change, but it is usually one that you can correct with Levels or Curves.

CJ Swartz
06-11-2003, 08:57 PM
Is that a select all and copy in the lightness channel and a paste into the blue?? Or am I confused now?

No, Chuck, YOU'RE not confused, but my fingers were when they originally typed the wrong word. It is corrected now...I think. ;)

Andrew B.
06-11-2003, 11:52 PM
If I may, here is an alternate method that I think provides greater flexibility.

1. Duplicate image.
2. Change duplicate to LAB
3. Click on the Lightness channel, Ctrl A, Ctrl C.
4. Back in the original image, paste the Lightness channel as a layer (not a channel) above the image.
5. Double click on this new layer to bring up the Layer Style menu.
6. Under Advanced Blending, uncheck R and G.

What you have now is the Lightness channel doing a nondestructiove replacement of the blue channel. And with this in place, you can dial in the blue channel with great flexibility.

For example, you can adjust the opacity on this new layer and it will give you a mix of the lightness and blue channel, and you will be able to see the result live, as you dial it in. Still not right? Copy and paste the green channel onto a new layer and group with the lightness channel. Now slide the opacity slider of the green layer. This will let you do live previews of blending the green with the lightness to replace the blue, or even just the green.

You can also add one or more adjustment layers, with or without layer masks. And it all works as long as you have everything grouped with the layer that is pointing at the blue channel.

This method can also be used for simply working on a single channel in a nondestructive way. For example, lets say you want to hand touch up the blue channel. Copy the blue channel and paste it as a layer above the picture. Uncheck R and G. Now do whatever touchup you want, use masks, adjustment layers, etc. on this.

Doug Nelson
07-24-2003, 04:10 AM
I have learned here at RP to always check my channels as the first step in any retouch job. It's a great tip, so I thought I'd pass along the "how to" of replacing a bad color channel. [details (http://www.retouchpro.com/tutorials/index.php/?m=show&id=23)]