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editing channels

Dec 10, 2011, 15:26
Post: #1
editing channels
Trying to make a "normal" map I downloaded and installed dds.exe and the normal map plugin. Got the Normal map as expected but apparently the rendering engine where I want to use the map has a glitch. Instructions to correct the issue were as follows:
"Create an alpha channel
Copy the contents of the red channel to the alpha channel
flood fill the red channel with pure black
flood fill the green channel with pure white"

the author of the instructions was using a different graphics program and I'm finding it impossible to figure out how to do in The Gimp can anyone list instructions as to how to manipulate the channels as listed above?

Thanks in advance
Gary
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Dec 10, 2011, 15:54
Post: #2
RE: editing channels
Although I searched before posting I could not find a relevant answer but after I posted the exact issue was listed as a "possible answer" directly below my post Smile
Problem is the answer wasn't explained the author says he found the answer in a wiki but doesn't list a link just gives the basic steps he performed. See here:
http://gimpforums.com/thread-solved-can-...h-channels

My problem is once I decompose the image becomes greyscale and I'm not sure how to proceed.
Gary
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Dec 10, 2011, 17:56
Post: #3
RE: editing channels
Done here on Red and Blue:
- open the Channels menu
- first save the Red channel for the alpha mask (we will deal with this later): drag the Red channel to the lower part of the list to create a copy
[attachment=778]
- de-select the Red and Green channels (in other words, only the Blue channel should be highlighted in blue)
- then bucket fill image with black (use the "fill whole selection" option)
[attachment=779]
- likewise select the Red, and bucket fill with white
[attachment=780]
- to copy the Red channel to the Alpha channel: Layer/Mask/add layer mask, and initialize with the Red channel copy you did earlier
[attachment=781]
[attachment=782]
- the Layer/Mask/Apply layer mask to finalize the mask.

Note that the indication I gave in the other thread (flood-filling a channel with white or black (or any given value for that matter)) can be done in the Levels dialog) is still valid.

Now answering your questions on
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Dec 10, 2011, 18:39
Post: #4
[Solved]RE: editing channels
(Dec 10, 2011 17:56)ofnuts Wrote:  Done here on Red and Blue:
- open the Channels menu
- first save the Red channel for the alpha mask (we will deal with this later): drag the Red channel to the lower part of the list to create a copy

- de-select the Red and Green channels (in other words, only the Blue channel should be highlighted in blue)
- then bucket fill image with black (use the "fill whole selection" option)

- likewise select the Red, and bucket fill with white

- to copy the Red channel to the Alpha channel: Layer/Mask/add layer mask, and initialize with the Red channel copy you did earlier


- the Layer/Mask/Apply layer mask to finalize the mask.

Note that the indication I gave in the other thread (flood-filling a channel with white or black (or any given value for that matter)) can be done in the Levels dialog) is still valid.

Thank you ever so much!
And may I compliment you on such a professional, well written solution

Gary
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Dec 10, 2011, 18:51 (This post was last modified: Dec 10, 2011 18:54 by ofnuts.)
Post: #5
RE: editing channels
Actually, the fast way is to use the Levels (Levels) tools (Color/Levels). To make the Blue channel all black for instance, you just force all the values of blue to be changed to 0:

[attachment=784]

And of course, the opposite move to set to 255 (flood with white)

Now answering your questions on
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Dec 10, 2011, 19:03
Post: #6
RE: editing channels
Smile Thanks for the follow up, I believe I'll get ample opportunity in the next little while to explore both methods so this additional (preferred?) option is greatly appreciated.

Gary
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