Re: [Gimp-print-devel] Image corruption

[Dave H. <da...@mi...>]

Robert L Krawitz wrote:
> 
>    Date: Thu, 10 Feb 2000 09:50:35 +0000
>    From: Dave Hill <da...@mi...>
> 
>    Robert L Krawitz wrote:
>    >
>    >    Date: Wed, 09 Feb 2000 14:51:21 +0000
>    >    From: Dave Hill <da...@mi...>
>    >
>    >    I have just tried printing some tests on my HP printer and I'm
>    >    getting an interesting image corruption. Basically, across the
>    >    bottom right of the image, there is a white patch followed by
>    >    a black patch at about 45 degrees.
>    >
>    >    I have gone back through my snapshots and the problem appears
>    >    between 0205 and 0206 - i.e. when the dither stuff was changed/
>    >    split out.
>    >
>    >    Has anyone else seen this?
>    >
>    > I haven't seen any problems on my Epson Stylus Photo EX.  Is your
>    > printer a variable drop size printer or single drop size?
> 
>    Mono Single drop size, using dither_black().
> 
> I can't see any obvious reason for this problem.  Is part of the image
> OK, but part of it messed up?

Yes, the lower right corner is messed up. What seems to happen is that
a white patch starts to creep in from the right hand side (long edge
of the paper), starting further to the left each row. Further down,
a black patch may start to appear from the right, although it sometimes
goes away again.

> 
>    > Oh foo, I think I know what the problem is.  You're probably
>    > seeing it in landscape mode, but portrait mode probably works
>    > fine.
> 
>    No, this was in portrait mode. I then went on to try landscape
>    and it's totally screwed up, you get the required output
>    squashed horizontally into half of the page and junk in the
>    other half!
> 
> What's the shape of the image?  Is it square, rectangular, which side
> is longer, what are the dimensions...

Landscape mode is now working after your change to the calling of
init_dither(). By working, I mean that it now has the same problem
as portrait!

The image I was trying is 190x110 (i.e. wider than it is high). I also
tried a 256x256 grey gradient which also doesn't work.

The effect varies as you change the scaling.

> 
>    I think I'm going to have to write a "hp_unprint" program to
>    save some paper!


This I have now done, I will submit it. It only handles mono 2-level
output at the moment, but it's a start!

It looks to me as if this problem is memory corruption. The "black"
buffer is getting overwritten by something else.

Dave

-- 
Dave Hill, Kempston, Bedford UK		da...@mi...
Sicth munce ago, I cutn't evun spel enjuneer, and now I are one!