Using preview mode to scan in color with UMAX Astra 600/610S.

Nicolas Lucas de Peslouan (
Thu, 04 Dec 1997 19:31:56 +0100

Hi !

I've done some more tests with the output from the Umax Astra 610S in
preview-color mode. (sane-0.68)

I worked with a "preview-umax:" file left by xscanimage after a color
preview. (I assume this is close enought to the true output from the
scanner to trust - at least - the bytes order). This of course also work
with the output of "scanimage --preview=yes".

The scanned image is a white paper, with 3 square: RED, GREEN and BLUE,
in order to find RGB signals.

The initial file show a three-column image, each column having the value
for one of the R, G of B signal level.

I first tried to swap bytes (R1R2R3R4...G1G2G3G4...B1B2B3B4... to

This gave a one-column image, but having part of the right side shown on
the left. (ABCD -> DABC), and some strang color change.

I then tried the same swap process but removing some noise at the top.
(about 185 bytes).

This work, showing a properly formated picture (ABCD) but having the
wrong colors. (red shown as blue, green shown as red and blue shown as

I then tried to remove more bytes, keeping the value "~185 in mind. The
correct noise length seems to be LengthOfLineInPixel*2+~185.

With this, we can have some sort of preview image.

But the image also shown some noise at the end, and some missing upper
margin at the top.

I tried to scan a white paper, and find that the noise at the begining
have the same values as the whole image. (form ~240 to 255). I then scan
a black paper, and find that the noise at the begining have again the
same values as the whole image (form 0 to ~32). In short, the "noise" in
not noise, but trailing bytes from a previous line.

At this point, we have to way to go :

- The scanner does not return the first few lines of the image, and we
need to request the image in another way.
- The scanner do return the first few lines, but they are lost/dropped

For now, we are able to convert some "preview-mode" image to something
readable, but with poor quality. (By the way, does anyone know the real
resolution used to do a preview ?)

If someone want to have a look at the quick-and-dirty C program to
convert from bad to better, just ask. It probably needs to be rewritten
to enhance performances, but...


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