On Nov 28, 2005, at 2:26 PM, Bob Shell wrote:
My understanding is that RAW gives you more shades of colors in
eachpixel and more opportunity to adjust colors in post
production, butjpeg or RAW, you still have 6 million pixels to
work with...no more,no less. So I look on RAW as just a way to
get better post processedimages, not anything to improve resolution.
It isn't RAW per-se that gives you more shades of colors. It is
the bit-depth of the file. Most everyday digital images we
encounter are 8-bit, meaning that for each color there are 256
possible shades. RAW files are generally 16 or 32-bit, meaning
that the space between no saturation and absolute saturation of
each color is divided into far more than 256 possible shades.
Millions of shades in fact. This is an advantage for depicting
subtle colors and shading. But remember that if your final file is
to be a JPEG, you'll have to drop it back down to 8-bit color
before converting to a JPEG. Photoshop was conceived as an 8-bit
editing program and is just now learning to do many of its
operations on files with greater bit depth.
Actually, most digital image files posted today are 8bits per channel
(24bits per pixel) nowadays. Still only 8 bits of information per
color, but the pixel composite is millions of colors rather than only
256.
Most DSLR sensors produce 12bits of grayscale information per
photosite. This allows 4096 possible grayscale levels at capture time
(theoretically 12 stops) but that's in linear gamma space. With gamma
correction to normal imaging space, the advantage of RAW over JPEG in-
camera rendering is between 7-9 stops of resolvable tonal space with
RAW format vs 4-6 stops of resolvable tonal space with JPEG rendering.
Post-RAW conversion translates the sensor's 12bits into a 16bit per
channel image space. This allow much greater flexibility in editing
vs working in 8bits per channel due to greatly reduced round off
errors. The result of having much more flexible editing is that you
can realize much more subtle tonal rendering in all colors.
Photoshop has been able to do some operations in [EMAIL PROTECTED] for
four major revisions now ... as computer systems power has increased
it has become feasible to do more and more. It can also operate in
[EMAIL PROTECTED] space on certain limited operations as well. In
general, if you've done a good job in RAW conversion and do most of
the remaining editing work in [EMAIL PROTECTED], the final required
conversion to [EMAIL PROTECTED] pixel depth can be virtually lossless with
respect to output device gamuts. Display screens for JPEG and printer
output to paper are only infrequently able to render tonal variations
with finer granularity than [EMAIL PROTECTED] can provide.
Godfrey
