[sane-devel] FW: Sane Scanimages Too Dark

Michael Watson mwatson33 at comcast.net
Sun Jan 6 23:08:19 UTC 2013

Thank you.
I just built and tested sane-backends 1.0.24git and the images are not as
dark.  I've found `gamma4scanimage 1.5 0 181 255 65535` to work about the
best.  And for text, "[0]0-[181]65535-[255]65535"

-----Original Message-----
From: Stef [mailto:stef.dev at free.fr] 
Sent: Sunday, January 06, 2013 3:54 PM
To: Michael Watson
Cc: sane-devel at lists.alioth.debian.org
Subject: Re: [sane-devel] FW: Sane Scanimages Too Dark

On 05/01/2013 01:45, Michael Watson wrote:

I may have answered one of my questions after researching the sane pages.
The "curve tool" is a transfer function graph.
Good stuff.
-----Original Message-----
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.





    I have recently fixed an issue with gamma table handling in the genesys
backend. This should improve the darkness issue you see. To test it you'll
have to compile the latest source code available from SANE's git repository.


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