How to create Alpha Channel for Coastal Tile in gimp

[+Baltika 85]

This is a guide on how to create an alpha channel for a coastal tile, or indeed any water tile, using the gimp software.

 

 

1. Open up your newly created coastal tile .bmp file.

 

2. On the main toolbar, under "Dialogues," open up the "Layers" and "Channels" windows as this makes it easier to keep track of what's going on.

 

3. From the main toolbar, click on Layer/Transparency/Add Alpha Channel. You will see your alpha channel appear on the Channels dialogue box.

 

4. By left clicking in the channels dialogue, highlight your new alpha channel and deselect the RGB channels, although leave them visible for now.

 

5. From the main toolbar, click on Layer/Mask/Add Layer Mask. A new dialogue box will pop up with a number of options. Select "Initialise Layer Mask" to "Layer's Alpha Channel," and click "Add." A completely

white box should appear next to your .bmp image on the "Layers" dialogue. That's the layer mask.

 

6. From the main toolbar, under the Layer/Mask options menu, ensure "Edit Layer Mask" is ticked, and that "Show layer mask" and "Disable Layer Mask" are unticked. Now, when you use any paint tool, you are editing the layer mask and not your image.

 

7. Select a paintbrush, colour black, and draw on the main screen to blank out the parts of the image which you do not wish water to appear on. The main image will go to grayscale, but in the "Layers" dialogue, you should see that your .bmp image is untouched, while what you are drawing appears on the white box next to your image. You can toggle the "show layer mask" setting to check this, but when it is visible you can't see your image so it's hard to know where to draw.

 

8. Once you have blacked out the areas you don't want to show up as alpha channel, toggle "show layer mask" to on. You should have an image which is partially black, where you have painted out the alpha channel, and partially white. The white part is your alpha channel. Using bucket fill, change the white to a shade of grey, with white being most reflective and dark grey being least reflective, depending on how much reflection you want from your sea.

 

9. Once you're happy, on the main toolbar, click on Layer/Mask/Apply layer mask. This is slightly disconcerting as the blacked out part of the image will turn to grayscale on all dialogues, but don't worry.

 

10. Select "save as," and save the edited image as a .tga file. Make sure you uncheck "RLE Compression" before saving. I don't know if "Origin bottom left" makes a difference or not.

 

 

Any comments, questions etc to Baltika.

 

Cheers all

 

Just remember, when working with TE - be safe out there, it's a jungle

Edited September 2, 2010 by Baltika