xscanimage / "gamma button" bug

Stanislav Brabec (utx@k332.feld.cvut.cz)
Sat, 22 Nov 1997 10:47:05 +0100

Hi sane developers,

I have found following bug in xscanimage / Astra 1200S:

If I press "custom gamma table" and then press "gamma" button, the
result of scan is bad (most light parts become darker and darker,
white becomes black).

But in other "custom gamma" selections, all is OK.

And more: If I press "gamma", then "save device settings", then "load
device settings", the custom gamma table semms to be the same, but
_works OK_!!! (This is the reason I am not sending setup file.)

This bug is really simply deferrable, but can cause many problems, if
you don't know about it.


Tips frontend: ==============

Batch scanning:

Due to stupidity of some users (includes me) please add option "warning overwrite" or "batch scanning". If this option will be on, user will be warned before overwriting files or, eventually, file will be written with new name.


Gamma button:

Gamma button in custom gamma table should remember it's value (in settings).


Color picker tool:

Color picker tool, which shows RGB values (original/after custom gamma correction) in preview window is very useful for good scanning.


Default filter

Default filter should be very useful "midend" option. Such external optional filter should perform some standard operation for scanning. The "midend" interface should be shell script filter with commandline arguments, which should represent scanner, mode (flatbed...), DPI, position on scanned area (x,y). Thus "midend" could for example perform:

Standard re-focusing (dependent on DPI) Standard de-striping (dependent on absolute position on scanner) Descreening (dependent on DPI and externally set LPI) ...and everything what user will prepare as script...


Gamma for >8bit scanners:

Now the gamma looks as follows: 0 0 0 5 5 5 5 5 5 11 11 11 11 11 16 16 16 16 16 21 21 21 21 21 21 27 27 27 27 27 32 32 32 32 32 37 37 37 37 37 37 Should be it interpolated?


Contract & gamma:

User could want to scan with custom gamma table, which represents gamma=value and contrast auto stretch. If you have picture with low contast, you can get also in such case level-smooth results in 8bit mode for >8bit scanners.

The simplest way to do it: add button for linear transformation of existing curve.


--Stanislav Brabec

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