[sane-devel] option threshold without effect for fujitsu backend since 1.0.24-1

[PELUARD Mickael]

Hello,

                we used Fujitsu scanner (fi-5110 / fi-5120 / fi-6110) for a long time with an old linux plateform and sane (1.0.22-9). These scanners used the fujitsu backend.

                We have recently changed to RHEL-6 with sane-backends-1.0.21 and to Debian with libsane-1.0.25.

                We scan in lineart mode and we only put the threshold option to reduce the size of document : scanimage -d 'fujitsu:XXX:XXX' --resolution 150  --mode lineart  --threshold 140
                Then we convert the image to PDF-A1. With the old plateform and rhel-6, no problem. But with Debian and sane-1.0.25, the size of the documents increase a lot.

Using a reference document, we get the following results with a fi-6110 :

-          Rhel-6 / sane-1.0.21 = around 50 ko

-          Debian / sane-1.0.25-2 = around 350 ko
It's quite the same problem if we used a fi-5110c and fi-5120c.

I downgrade the libsane package and look the result :

-          Debian / libsane-1.0.22-7 = good

-          Debian / libsane-1.0.23-3+b1 = good

-          Debian / libsane-1.0.24-1 = NOT GOOD

-          Debian / libsane-1.0.24-8u5 = NOT GOOD

-          Debian / libsane-1.0.26Git = NOT GOOD

I change the value of threshold on Debian with sane-1.0.25 : threshold 0 or 200. But the image don't change. It's look like the threshold option has not effect.
To reduce the problem, I play with the contrast and brightness option but the result is not entirely satisfactory.

I think the problem is on the threshold option of the fujitsu backends.

It is probably the same bug but it don't lokk corrected in 1.0.26 :
https://alioth.debian.org/tracker/?group_id=30186&atid=410366&func=detail&aid=315069

Cordially.
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