With my Brother MFC-J825DW, the output of 'scanimage --help' includes this.
Code:
Options specific to device `brother4:net1;dev0':
Mode:
--mode Black & White|Gray[Error Diffusion]|True Gray|24bit Color|24bit Color[Fast] [24bit Color[Fast]]
Select the scan mode
The default mode is '24bit Color[Fast]', but this does not work for me. I need to use '24bit Color' instead. This can be selected in xsane.