[sane-devel] Parameter Default Values

[Kåre Särs]

On Wednesday 11 April 2007, Olaf Meeuwissen wrote:
> I should have added that the epkowa backend also contains an ever
> growing list of model dependent matrices in epson_scan_hard[].  Each
> entry may specify up to four matrices, one for reflective originals
> (paper, etc), colour negative, B/W negatives and colour dia positives.
> IIRC, the B/W negative matrices are always the identity matrix.

If I understand this correctly the values are "calibrated" for the different 
models and scan sources (and should be sane :).

> You originally wrote:
> > The problem I have is that the default values for the color correction
> > parameters ('cct-1' -> 'cct-9') give me a yellow page (original is white)
> > when I write back the original value to one of the parameters. If I don't
> > touch any of the cct parameters I get a white page.
>
> I assume you have checked that when you "write back the original
> value" that that's indeed what gets set, right?
> There might be endian issues and SANE_FIX/SANE_UNFIX confusion.
>

The problem I had earlier was probably that the "write back the original 
value" was a little off :(. 
As you can see in my last post I now get a good image :). I could not 
reproduce the "yellow" image, but wondered where the "magic" numbers came 
from.

> > BTW today the image is quite fine even tho the paramete values are
> > quite 'magic' :)
>
> Your debugging output quite nicely matches, within floating point
> precision, the entries for the RX500/RX510.
>
> > I also noticed that changing the film type when scanning with the
> > transparency unit changes these (cct) values.
>
> See my first comment above as to why.
>

> None of your setValue() calls seem to try to set one of the cct option
> values.
>

In the my code, the sane options are 'connected' to GUI objects that write the 
values to the backend when the user changes the values. When I sent the first 
mail, the GUI Object probably modified the value and wrote it back to the 
backend modified. Since then I have modified the change quantization step 
size of the GUI objects.

The important question for me was "Might there be a need to modify default 
values to get a good image". If I read your answer correctly the answer would 
be "No" at lest for these parameters.

Thanks,
  Kåre Särs

PS. My project can be found at SourceForge:
http://sourceforge.net/projects/sanewidget/