Compression: Color/grayscale or 1-bit

Allows you to check the compression mechanism used for either color and grayscale or black and white images.

Depending on the type of images you are dealing with, different compression methods are recommended. Using the appropriate compression methods can significantly reduce the file size of the PDF document. For an overview, refer to Compression mechanisms explained.

Possible fixes

You can automatically change a particular image compression to a particular format:

Color or grayscale images can be changed to ZIP, JPEG or JPEG2000 (for the last two options, you should also specify the desired quality level).
1-bit images can be changed to ZIP or CCITT.

For an overview, refer to Compression mechanisms explained.