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Working with alpha / separating channels


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Hi all,

I'm working on some texture files for the game Fallout 3, and was pointed to PDN, since it has support for the DDS files used by the game. I've been able to use the eraser tool to some extent to create transparent portions of a layer when combining multiple layers, but it seems to be missing some functionality, plus I need to be able to edit the alpha layer separately from the other channels.

I can't remember what image editing software I used before, but it belonged to my workplace, so I couldn't keep it. Anyhow, when you used the eraser tool, left-clicking raised the transparency by whatever settings the tool was set, and right-clicking lowered the transparency. This way you could easily get the transparency just right. However, I don't see any such option with PDN. In fact, I'm not even sure how to just make the image completely opaque so I can start from scratch.

Next, it would be tremendously easier if I could separate the different color channels (specifically alpha) into either different greyscale images or different layers, work on them individually, then recombine them into a single image. I found the Alpha Map plugin that lets me convert the alpha channel to greyscale, but when converting the greyscale back to alpha I'm left with no RGB information. Copying the original RGB information seems to also copy the original alpha information, over-writing any changes I made using the alpha plugin. Any ideas on how to edit the alpha layer without saving as a file-type that doesn't have transparency to make it opaque then manually using the eraser and hoping I don't make a mistake?

The game uses the alpha layer as its own greyscale image (i.e., it's using RGB to make a 24-bit image and alpha to make a separate 8-bit image), so it's easier to work with if I can see just the alpha layer, instead of trying to guesstimate what it looks like based on how transparent the image is. I'm sure there's probably something stupidly obvious, but I'm not seeing it. Any help would be appreciated. Thanks!

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I'm not quite sure I understand your issue fully, but you might want to try the Faking Soft Brushes and the Blur/Dodge/Burn tool tutorial by Wither... soft erasers are in there as well. The soft eraser method is a little tedious, however. You might also want to look into BoltBait's Transparency plugin, which is useful when you have slightly transparent image that you want to make opaque, or vice versa, without using layer transparency.

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User BoltBait has written a plugin known as Alpha to Greyscale. Use that plugin to extract the alpha channel into an editale greyscale, then save the greyscale layer and load it in using the alpha mask plugin. This should be the simplest way in editing the alpha channel directly.

As well, the eraser tool works exactly as you described. Left click will reduce the transparency based on the alpha level of your primary color while a right click will edit the transparency based on the alpha level of your secondary color.

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I hate to do this, but seriously, I think you should try a different program. PDN just doesn't have the individual channel editing features you need at this time, and the workarounds are anything but intuitive.

I'd suggest giving The GIMP a shot - I'm a professional web designer, and it's what I've been using to do my day-job for years, so it too comes highly recommended. As long as you don't let the first impression the UI gives put you off, you'll find a very powerful, legally free photo editing app waiting for you. It has individual channel editing capability (all four RGBA channels), direct Alpha Mask editing, anti-aliased selections, soft brushes... and it even has the two-way eraser function you mention (set the opacity slider in the tool options box, then Left Click to lower by that amount and [Alt]+Left Click to raise by that amount).

It does not natively support the DDS filetype, but like PDN, there is a vast plugin repository, such as this DDS filetype plugin I found via Google search.

PDN definitely stomps The GIMP in UI friendliness, but The GIMP has been in production since 1995, so it's a deal more feature-complete, and it's an incredibly powerful piece of kit once you get a feel for it.

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I am an organism, an animal, a creature, I am a beast.

~ Becoming the Archetype

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Thanks for the tips! I'd found the alpha map, which extracts alpha to greyscale, and with the alpha mask you suggested I can import greyscale back to alpha, which is exactly what I needed.

I tried GIMP, and it does have the nice eraser brush. Now, if PDN would just recognize GIMP's copy buffer it would be perfect. :) I've figured out how to extract the channels using GIMP, but not how to switch them or import them yet, so that's not quite solved, but since I just needed the alpha layer, I can use the PDN plugins.

Thanks again!

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