Replacing Installer Style > Wizard Dialog banners

I've spent an hour trying to figure this out, but with no luck. I am trying to replace the default Wizard dialog bitmap banners with my own BMP images. The default banner images are 164x314 for the side, and 55x55 pixel for the top. But when I create replacement BMPs at these dimensions, the images are always distorted. To debug this problem I created two new images of these sizes and on the images placed a black and white grid, where horizontal and vertical black lines are 1 pixel apart. When these images are used and the installer package built and run, the uniform grid turns into a distorted plaid design.

What does one have to do to create non-distorted replacements for the top and side Wizard banners?

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