To make a coloured background work, pick your figures carefully. These are the big three pixel-based image formats.
JPG: This is the most popular and familiar format. It is used on the web routinely because it has a wider color range than previous formats (24 bit), and generally has smaller file sizes than other formats.
GIF: This format is older than JPG. It can’t render as many colours as a JPG (8 bit). You can also create short animated images in GIF format, though you couldn’t use that on a poster.
PNG: This GIF successor can render 24 bit colour.
One important difference between these formats is transparency. Here’s a demonstration:
The JPG on the left looks shoddy compared to the GIF on the right.
JPG images can’t do transparencies. Every pixel must be coloured. Images that fine against a white background, like a white sheet of paper, can suddenly be floating in a white rectangle on top of your beautiful poster background. And suddenly, you have started down the road to boxism.
GIF and PNG images can do transparencies, which can allow any underlying colour to show through. It’s not automatic; you do have to watch the setting when you’re saving the image.
If you have an existing JPG that you like, one workaround is to match the space around your image with your poster background. This isn’t difficult if you have a simple background colour, but quickly becomes a headache if you want textured or shaded background.
But if you’re going to go to that much effort to edit the picture, you might as well mask out the background areas, then save a copy in PNG format. This can take a little fiddling in your graphics editor to do, but the result is worth it.
Will it scale?
Never let them see your pixels
Wednesday Surgery on Jim Campbell’s Comic Book Lettering Blog