RetouchPRO

Go Back   RetouchPRO > Technique > Image Help
Register Blogs FAQ Site Nav Search Today's Posts Mark Forums Read


Image Help Got a problem image? Don't know where to begin? Upload images and ask our users what they think or if they can help

channels

Reply
 
Thread Tools
  #11  
Old 03-20-2005, 08:28 PM
Duv's Avatar
Duv Duv is offline
Senior Member
 
Join Date: Oct 2003
Location: Nanaimo, British Columbia
Posts: 1,213
By the way, here's a quick way to reduce a lot of the cracks. Select your Clone Stamp tool. For the wall, set blending to Lighten. Sample and paint and you should see a lot of the dark cracks reduce or disappear. Change to Darken mode for light cracks on dark background.

Cheers
Dave
Reply With Quote top
  #12  
Old 03-21-2005, 09:55 AM
hpycmpr hpycmpr is offline
Member
 
Join Date: Feb 2005
Posts: 36
The good and the bad

I'm at a stage to learn how to use channels to enhance photo realistic images beyond what Curves can do, but have found it rather challenging. So thanks for the links, CJ. They are great complements to the Eismann and Margulis books. The second link is outstanding in walking through what channels are and how to make use of them. It is by a Canadian web designer! What gives, DUV?

As Margulis points out, each image has ten channels available to work with. But I find it difficult to come up with a strategy to use them properly. Without a strategy, the trial and error approach is rather frustrating. I suspect my problem is due to a lack of understanding of one or more of the following, and would appreciate some help:

- what makes a channel "good" (or "bad"), and how to identify each?
- is "good" and "bad" relative to what one wants to achieve (I think so)?
- after correcting/replacing a single channel, or merging channels, an image's colors may change unexpectedly. Is there a way to anticipate what changes may result?
- is it more appropriate to correct with channels first before applying Curves or other tools, or vice versa? If this depends on the situation (I think so), are there suggestions on how to handle some common situations?

Thanks in advance.
Reply With Quote top
  #13  
Old 03-21-2005, 02:51 PM
Duv's Avatar
Duv Duv is offline
Senior Member
 
Join Date: Oct 2003
Location: Nanaimo, British Columbia
Posts: 1,213
What gives hpycmpr with the "What gives, Duv?" Seems to have come out of the blue.
In any case, some people here may have the skills to teach you everthing you need to know about channels. Unfortunatly, I can't nor do I have the time. Channels can be used for a host of reasons: one channel may have too much noise, not a good thing. A stain or colorcast may show up less or not at all in a channel so you can blend into another channel with the cast. You can use channels to create an Alpha Mask for extraction purposes. Also, you have to develop a workflow that works for you. I haven't done it but perhaps a good starting point is to check your channels before you do anything else. I think that would make sense.
I've simply learned from many of the sources you refer to. Maybe the best source is Katrin Eismann's new book, Photoshop Masking & Compositing. There's a ton of good info on channels and how to make them work for you.

Good Luck
Dave
Reply With Quote top
  #14  
Old 03-21-2005, 04:46 PM
BayCanuck BayCanuck is offline
Junior Member
 
Join Date: Mar 2005
Location: Calgary, Alberta, Canada
Posts: 7
On channels

Well, to start with, you have a black and white image that's been scanned in colour. So the three "colour" channels are just what your scanner saw with different colour filters. Unless you want to colourize your image, your end product should be a one-channel image, because one-channel gives black and white.

You asked what makes a channel "good" and then answered your own question: A good channel is one that gives you the closest approximation of what you want to do with the least ammount of work.

For this image, I'd choose the red image, since it's showing the least ammount of "problems" that you have to fix, and hasn't lost very much information in the highlights compared to the green channel. Generally, for B&W images scanned in colour, the "noise" (badness) per channel is least in red, most in blue, and kind of in the middle for green.

How I determined this was to "normalize" all the channels, then look at them one by one. To normalize them, I pulled up Image->Adjustments->Levels, and used the drop-down in the levels dialog box to select each of the red, green, and blue channels in sequence. Then I dragged the small triangles right under the histogram to the "edges" of the histogram (for each of red, green, blue) and then clicked OK. This made sure that the tonal (light tone, dark tone) representation of each channel was the same.

To evaluate them, I used a keyboard shortcut: Control-1, Control-2, Control-3. This shows only the red, green, and blue channels respectively one at a time. Notice to the left of the young girl's hair how the "dirt" gets bigger and more defined as you go from red->green->blue (1->2->3.)

Since Red has the least problems, I'd select it (Control-1, or use the Channels pallette and click the eye icons so that only the "red" channel's eye is on,) then convert it to greyscale (Image->Mode->Greyscale.) Now you only have one channel to worry about, and there's no problems with colour casts.

For right now, I'd not worry too much about the "ten channels" metaphor. That becomes more important when editing colour images, not black and white ones. Since this is a scan of a black and white image, all those other channels are really combinations of the information you already have in the red-green-blue channels. Since I think the Red channel was already the best, any of the other seven channels is really some part of the (good) red channel plus or minus some part of the (bad) other channels. You can't make good better by adding bad.

Good luck with the image!
Reply With Quote top
  #15  
Old 03-21-2005, 05:17 PM
jonk's Avatar
jonk jonk is offline
Member
 
Join Date: Feb 2005
Location: Ohio
Posts: 54
Question for Dave

Hi Dave,

It looks like you use the channel replacement as much as I do. Maybe you can answer a question for me that has been driving me nuts! Note – I am using Photoshop CS.

When you open the [Apply Image] menu option box, the target channel is already set to the primary selected channel. In order to have the correct target channel selected you have to select that particular channel in the channel palette before opening the [Apply Image] menu option. You would think that you would be able to select the target channel from a drop-down option box just like the source channel option.

Do you know of a way to select the target channel another way?

Did this make sense?

Thanks!
Jon
Reply With Quote top
  #16  
Old 03-21-2005, 09:41 PM
Duv's Avatar
Duv Duv is offline
Senior Member
 
Join Date: Oct 2003
Location: Nanaimo, British Columbia
Posts: 1,213
Hi Jon. I think what you need to do is click on the Mask box. That will open some other options including Channels where you can choose the one you want.
Let me know how it goes. BTW, has Spring started in Ohio yet?, I'm an old Ontario boy.

Cheers
Dave
Reply With Quote top
  #17  
Old 03-22-2005, 08:18 AM
jonk's Avatar
jonk jonk is offline
Member
 
Join Date: Feb 2005
Location: Ohio
Posts: 54
Hi Dave!

Thanks for getting back with me. I have opened the Mask option box, but I am not sure if the [Mask] [Channel] is the same as the target channel. I have included a snapshot of the Apply Image option box so you can see what I mean.

Spring in Ohio – BOY I WISH! It’s still cold here but at least the sun is out today. Last year I was traveling all over the country. I'm glad to be home for awhile. Maybe I can get some work done around the house.

Thanks again for the help and talk to you later!
Jon
Attached Images
File Type: jpg channelselect.jpg (86.6 KB, 14 views)
Reply With Quote top
  #18  
Old 03-22-2005, 08:29 AM
Duv's Avatar
Duv Duv is offline
Senior Member
 
Join Date: Oct 2003
Location: Nanaimo, British Columbia
Posts: 1,213
Jon, don't worry about that. At the bottom of the box you'll see Channel: Grey. You can go in there and change to the channel you want.

Dave
Reply With Quote top
  #19  
Old 03-22-2005, 09:30 AM
jonk's Avatar
jonk jonk is offline
Member
 
Join Date: Feb 2005
Location: Ohio
Posts: 54
Thumbs down

Perfect! Thanks Dave!

I was not sure if that was the traget channel. I guess I should have played around with it a little.

Thanks Again!
Jon
Reply With Quote top
  #20  
Old 03-28-2005, 07:38 AM
hpycmpr hpycmpr is offline
Member
 
Join Date: Feb 2005
Posts: 36
Canadians

Quote:
Originally Posted by Duv
What gives hpycmpr with the "What gives, Duv?" Seems to have come out of the blue.
I was referring to the second link suggested by CJ. The tutorial was written by a Canadian. It is simple and logical to understand, and yet covers lots of ground. Makes me wonder if the Canadians are specially good at this kind of thing.

Quote:
Originally Posted by Duv
In any case, some people here may have the skills to teach you everthing you need to know about channels. Unfortunatly, I can't nor do I have the time. Channels can be used for a host of reasons: one channel may have too much noise, not a good thing. A stain or colorcast may show up less or not at all in a channel so you can blend into another channel with the cast. You can use channels to create an Alpha Mask for extraction purposes. Also, you have to develop a workflow that works for you. I haven't done it but perhaps a good starting point is to check your channels before you do anything else. I think that would make sense.
I've simply learned from many of the sources you refer to. Maybe the best source is Katrin Eismann's new book, Photoshop Masking & Compositing. There's a ton of good info on channels and how to make them work for you.

Good Luck
Dave
Thanks for the suggestions. I know how to create mask or selection from a channel, but need to understand more about channel blending. Eismann's Masking book is in the mail, I hope it can address some of my questions.
Reply With Quote top
Reply

  RetouchPRO > Technique > Image Help


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Tutorial 05: Converting a Color Image to Black and White grayscale BW DannyRaphael Photo-Art 101 17 05-22-2011 05:55 PM
Channels Prisma Photo Retouching 8 08-10-2007 01:53 PM
channels Gina_D Image Help 15 06-01-2006 06:58 AM
Elements and Channels Andrew B. Hidden Power Support 30 03-12-2003 05:35 AM
RGB Channels Doug Nelson Photo Restoration 0 08-08-2001 12:08 PM


All times are GMT -6. The time now is 04:19 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
SEO by vBSEO ©2011, Crawlability, Inc.
Copyright © 2016 Doug Nelson. All Rights Reserved