Discoloration on transparencies

[prussiah]

I've been trying to make a piece of pixel art I created into a transparent GIF that is currently a BMP. I do the normal steps in using a solid colored background, saving as a compuserve GIF and selecting a transparent color during saving. For some reason, however, the final image has colored pixels all over the non-transparent portions. I've tried saving other items in the same way and had no issue.

Here is what I mean:

[Sam_Zen]

Well, obviously your original bitmap didn't have that solid background after all, seeing the upper example.
While it may look solid when viewing the whole picture and one has to click on a background color to make it transparent.

Better do a inter-action in this case to make sure that the background color is one, by using the FloodFill tool of the IVPaint (F12) first.

First select the main desired background color with the color picker. Then use the FloodFill by experimenting with the Tolerance value.

[prussiah]

The examples posted are just enlarged screen caps for example. The actual background is all solid bright green, and that has been checked in both MSPaint and with the floodfill tool on irfanview. The color in the background being solid isn't the issue.

[matera]

What is the color depth of the original?

[j7n]

IrfanView is doing dithering because a GIF can't have more than 256 colors (8-bit). To have more control on what colors are preserved, use Paint Shop Pro.

If there are less than 256 colors in your picture, choose Octree method in the color depth decrease dialog. All colors should be preserved exactly in the palette. If there are more colors, some dithering will take place. Other methods will always dither and won't count the colors beforehand. Alternatively you can use the PNG format, which can have 24-bit data. (File -> Export -> PNG Optimizer)