color correction & vignetting [Re: [ptx] Hugin wishlist, RFC]

[Pablo d'Angelo]

On Wed, 04 Feb 2004, Glenn Barry wrote:

> On the subject of colour correction I have a Fuji S1 which has uneven colour
> from one side of the CCD to the other, I've made photoshop actions to
> correct for this and vignetting when using the Sigma 8mm fisheye, but the
> way I did it was to photograph a white evenly lit piece of paper and use the
> RGB channels as masks for the colour correction.
> 
> I don't know how prevalent uneven colour across CCD's is but what would be a
> great feature would to be take a calibration shot of a piece of evenly lit
> white paper and use the light falloff/vignetting to calculate values for a
> particular lense aperture combination and save those settings for radial
> luminance correction.

Hmm, with a flatfield correction (for each channel separately), this should
be possible, much like you do it by hand right now.

> Now sorry for the rant, but if you have a calibration shot for a certain
> lens/aperture you can adjust for any differences in light falloff and
> vigentting from a known reference point. This may also help with calculating
> colour correction for shots all taken with the same settings for any given
> panorama. I know this adds one more step to maing panoramas, but given that
> FOV, A, B and C calibration is a good idea anyway, the extra step to record
> colour variation may make totally seamless output a reality.
> 
> What does anyone think?

While I haven't heard of the problem your camera has before, it might be
nice if these errors could be corrected as well.

And, yes, this correction is needed for color correction and stitching, but
it'll take some time until the current SIFT feature stuff etc. has been
integrated. 

> 
> BTW I am going to try and Port Hugin to SGI Irix as I've got an SGI Box here
> that I want to make more use of(meaning fumble around and try to get it to
> compile, about which I know next to nothing, but you have to start somewhere
> ;-)

Theoretically it should be quite straightforward, if wxwindows and vigra are
supported.

ciao
  Pablo
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