>
> ACR would have had the problem fixed some time about June 2004 (a year
> after the E-1 was announced). But I do find this whole thing somewhat
> curious. If the bug is failure to interpret the RGBG pattern for
> correct demosaicing how is it that the problem only seems to occur in
> very bright highlights and only when converting directly to JPEG.
> Sounds like a pretty ordinary bug to me and not something systemic
> driven by the Bayer pattern.
>
Chuck, the way I understand it, at issue is how the nearest neighbor
calculation is performed to determine color.
The Olympus pattern is designed as a four-pixel (RGBG) quadrant whereas the
more typical array is the triangle of red, blue and one green.
You wouldn't see any difference (other than some color-space/gamut shifting
which is another nasty byproduct of incorrect demoisiacing) in most of the
range of colors and intensities, but once you get in the top stop of dynamic
range, the conversion breaks down and what was intended to be a four-pixel
quadrant with two greens no longer is able to handle the highlight
transitions.
If you work the math and attempt to manually recreate a demoisiac of the
array you can see where it could fail in certain color and brightness
combinations. The demoisiacing algorithm has to calculate two different
things for each pixel position: Brightness and Color. Depending on the
algorithm used, the assigned pixel brightness and color is determined by the
combination of three pixels, four pixels or nine pixels. The algorithms use
up to nine pixels to determine color for any specific pixel. If you use only
three pixels to determine color assignment, you run the risk of color
sparkles and maize patterns. The actual luminance value of these patterns
and sparkles is the same as neighboring pixels, but the color is wrongly
determined. When you increase the number of pixels used in the algorithm the
sparkles and maize patterns usually go away.
Rumor has it, and I have not been able to confirm it, so take it just as
hearsay, that the Olympus sensor uses two different types of green pixels
with slightly different wavelength sensitivities--not too different than the
Sony sensor used in the DSC-F828. I would dispute that claim based on
extensive research and detective work of the Kodak CAF sensors used in the
E-1, E-300, E-500 and E-400. However, it would not be beyond the realm of
possiblity that the pigments used in the Panasonic supplied Olympus sensors
are different than the ones used in the Panasonic sensors. Doubtful, but
possible.
AG (moisiac) Schnozz
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