Raw image file
When image data is stored on disk as pure pixel values with no header information whatsoever, it is a "raw" image. This is not to be confused with RAW format photographs produced by DSLR cameras.
If storing a basepalette, the file should be saved as 24bpp RGB with any dimensions that multiply to 256, such as 16x16, 32x8, or 256x1. The resulting file should be 256 indexes x 3 color channels = 768 bytes in length.
For a palookup, the file should be saved as 8bpp indexed, again with dimensions that multiply to 256. The resulting files should be 256 bytes. If you are loading a palookup that includes a shade table, multiply these values by the number of shades you are using, usually 32.
For a blendtable, the file should also be 8bpp indexed, with dimensions of 256 by 256, and the file should be exactly 65536 bytes.
You can use IrfanView to load and save raw images.