Originally Posted by karenbryant
Also, how do I reduce the color depth to 16 levels of gray-don't really understand!? Is there some way of doing that for all pictures in one go?
Thanks for your help; much appreciated.
To do this you need an image editor or image conversion program. You would extract copies of the images from the epub, edit them with an image editor (e.g. Adobe Photoshop, Corel PhotoPaint, Gimp, ...) to make the changes, and then copy the edited image back into the epub to replace the originals.
The epub file is really just a specially organized ZIP archive. If you change the extension from .epub to .zip you can get access to its contents. Simply display the contents (on Windows a simple double-click on the ZIP is open a window), navigate to the images, and drag out copies. Edit those copies and then drag them back into the same folder overwriting the originals in the ZIP. Doing it that way you don't disturb the special organization of the other files in the epub. When done, simply change the .zip extension back to .epub and test the file.