[sane-devel] FW: Sane Scanimages Too Dark
mwatson33 at comcast.net
Sat Jan 5 00:45:39 UTC 2013
I may have answered one of my questions after researching the sane pages.
The "curve tool" is a transfer function graph.
From: Michael Watson [mailto:mwatson33 at comcast.net]
Sent: Friday, January 04, 2013 5:28 PM
To: 'sane-devel at lists.alioth.debian.org'
Subject: Sane Scanimages Too Dark
Request insights from the brain trust. Sane scanimage files are too dark
while windows' scans (Canon drivers/applications) are fine?
I have an archlinuxarm box and an Lide210 scanner. Utilizing SaneTwain on a
windows box the network scans were too dark. Similarly, scanimage (local)
scans were also too dark. Trying to compensate the SaneTwain gamma was
experimented with. What worked well was a straight line curve that maxed
out at the top while 3/4 of the way to the right (0,0 --> 191,65535 -->
65535, 65535) and not the top right corner ((0,0 --> 65535, 65535).
With this information the scanimage (local) was adjusted with
gamma4scanimage 1.75 0 181 255 65535, which works well.
I do not understand why the upper limit is at approximately 191 and not 255.
>From the sane debug it appears the gamma is initially set to 1.7, which
produces dark images because the initial gamma table is equivalent to
gamma4scanimage 1.7 0 255 255 65535?
[genesys] sanei_genesys_create_gamma_table: size = 256, maximum = 65535,
gamma_max = 65535, gamma = 1.7
Also, SaneTwain will send the gamma table to the scanner when initially set.
If it is saved (ini file) and SaneTwain is started up, the custom gamma
table checkbox (custom-gamma=yes/no) has no visible impact on the scanned
image - too dark.
Any insights appreciated.
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