Yes. I believe that's right. The article referenced of course presents the
failure to utilise internal interpolation, and that you have to convert "by
hand", as an argument against RAW. I'm thinking that the ideal format would
be a file containing the Bayer data as well as additional information
representing *one possible* transformation - so that the file might be stored
or displayed as RGB without no user interaction, while you also retained the
opportunity to use completely different interpolation parameters. But maybe
they do this already?
None that I know of do this. I think the difference is that TIFF
format allows for other *colorspaces* (Lab, CMYK, etc)... the Bayer
pattern is a slightly different animal. It's not really a colorspace so
much as spectral spatial filtering on an RGB image. One could certainly
define a baseline interpolation routine, but that's beyond what TIFF does.
I, personally, think that the Bayer is a good compromise. It provides
luminance information at every pixel location. The chroma is downsampled
(2:1 for G, and 4:1 for B and R). Since that's not too far from visual
perception, it seems like an acceptable way to go.
It seems to me that what exactly constitutes "luminance" is still an
assumption, though. I'm wondering what the results might be like if they also
included some elements with no filter at all. Didn't Fuji or someone try
that, by the way?
I think some have used CMY, and some CMYK. I don't know for sure.
Luminance is fairly well defined, for an individual pixel, I'd say. If
you look at the datasheet for the sensor, it's got the respective pixel
color spectral response. The output is the integral of that (i.e. filter)
and the incident light. Mapping that to the human eye response (XYZ
space) is where it gets ugly.
I think they sorta did that. The TIFF has a number of funky tags in
it. Some are obviously proprietary.
This actually touches on some other recent discussions on the list, since
what you're saying here makes me think that the Pentax engineers do indeed
know what they are doing; taking an existing format and adapting it just
enough to suit your special needs (when there is nothing available already
that does) is good engineering, IMO. Divining yet another way that's
incompatible with everything else to represent a picture would not be...
Differently put, it seems like Pentax have done this exactly the way I would
have ;-)
Pretty much... 'cept for the issues I've raised with technical
support. The biggest is the choice to have a full-blown (but yet low
quality) JPEG in the RAW. I'm sure they did it so it takes less CPU to
zoom in on camera and in their gimpy bundled software. The TIFF format
for the -DS even tags the data as compression type "PackBits," even though
it's not quite what it actually is. Packbits is a RLE compression... they
abused the standard and called Packbits two 12-bit numbers in three bytes.
A play on language, perhaps... :)
-Cory
*************************************************************************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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