When converting a 24-bit image to a 256 color image, the HTML Help Image Editor will give you two choices for conversion:
Graphics (optimized). Select this conversion for images that contain photographs or conceptual art. The HTML Help Image Editor will convert the image so that it uses the the HTML Help Image Editor 256 palette. This palette will be the same no matter what image is converted.
Windows (standard). Select this conversion for screen captures that do not contain photographs or conceptual art. The palette may not be the same for each image. To use the same palette, first convert the image using the Windows
conversion, and then use Convert to the HTML Help Image Editor Palette. This will force the image to use the same palette as a graphics conversion.