[sane-devel] Any way that I can have sane/xsane automatically detect each paper's dimensions?

[insaneme.9a at recursor.net]

Scanner: Brother ADS-2000 (automatic document feeder)
OS: Linux Mint 17.1 Cinnamon,  64-bit
xsane: 0.998
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Dear all,

When using xsane, it seems that I must manually select the dimensions of
the papers. Is there no way that xsane or sane can automatically detect
each paper's dimensions?

Currently, my xsane has "paper size" set to Manual, and all the PNGs
produced have so much white space around. Please don't tell me I have to
crop each page (like, in Gimp)! If xsane/sane can't automatically detect
each paper's size while the scanning is happening, is there some software
that can automatically crop each image/PNG that is saved/produced by
sane/xsane?
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