Here you can define the color depth of the resulting BMP file. The color depth is the number of bits per pixel. The default setting is Automatic which means PhotoLine is calculating the color count in the image and uses the optimal color depth. But if you have a special usage, it may be necessary to set a fix color depth.
Furthermore you have the option to automatically reduce the number of colors when saving in the BMP-format. You may also turn on Ask. In this case on saving the Color-Reduce dialog is shown, otherwise the reduce scheme selected in Preset will be used for reduction (see chapter 5.7.2).