The four test images below were created for testing colour image edge detection algorithms, but they probably have other uses too. They are 24-bit RGB colour images.
These images are made freely available, but I retain copyright in them. If you use them in a publication, all I ask is that you credit the source of the original image. (Acknowledgement: The saturated colour bars image is based on a video test pattern. Robin Horne first made me aware of this pattern, which is easily generated from a 3-bit natural binary sequence with one each of red, green and blue controlled by one bit.)
The images are available in Portable Network Graphics (PNG) format only. If you need a different format you can convert the images using an image viewer or editor. Likewise if you want a horizontal colour bars image you can rotate the vertical bars image using an editor. All four images are 512 pixels square. You can obtain smaller sizes by resampling.
The isoluminant versions have constant luminance across the image. The normal versions have fully saturated primary and secondary RGB colours. The PNG files contain palette images, since this provides compact files with no loss of colour information (since the images contain only 8 colours).