2008-01-06 by Paul D. DeRocco
> From: Clayton Price
>
> First, assuming your premise of not saving an edited RAW image is
> correct, then one would
> ask what you think a DNG image is? ACR, which improves quite a bit
> with each new iteration,
> has opened the possibility of doing an overall edit of any
> RAW image.
> When saved as DNG, or
> for that matter, simply clicking "done" in ACR will save the changes
> to the original raw file, and it shows
> up in Bridge with a small symbol indicating that it's been edited.
> One can go back to the original
> raw image anytime they wish, simply by opening the image from the
> folder in which they are
> stored -- in Bridge, then clicking, which opens it again in
> ACR. This
> is more than likely true for Light Room as well
> (I don't use it, so I'm not sure). If the image is saved as DNG, a
> simple double click will directly open in ACR, where you
> can change the RAW settings at will, and clicking "done" saves the
> changes - period. That's because, in simple terms,
> the DNG saves the instructions one has adjusted, in what is becoming
> a universal format, and it opens showing
> those instructions (read: editing)! How does that translate,
> in your
> words, to RAW files being read-only?
As far as I know, no Adobe program ever modifies a camera's raw file;
instead, it stores the "edits" made in the raw converter in XML form either
to a sidecar .xmp file or to a central database, depending upon how
Photoshop is configured. On the other hand, DNG is an Adobe standard format
for raw (i.e., still Bayer encoded) camera data, so Photoshop probably does
store those conversion tweaks as XML embedded inside the DNG file. But in
any case, none of these "edits" are actually modifications to the pixel
data, they're just records of how the various sliders are set.
> To tie this together: Printing -- Many people can obtain their
> maximum needed quality just from RAW adjustments of their
> files. I suppose going straight to print, without assigning a format
> other than RAW or DNG to the file would work for them --
> I don't know much about printing that way - I'd guess there is some
> sort of automatic conversion to a printer-recognizable
> format (jpg, I'd imagine), because to my knowledge, and I'm no
> beginner, printers need pixels to print an image. The better
> the pixel quality, the better the prints, which is why a 300 ppi
> files will print better than a 120 ppi file, and some of us
> use a 720 ppi image to maximize carbon pigment prints.
>
> That said, I would venture to suggest that for most people on this
> list, printing images straight from RAW, as opposed to the
> opportunity to make the myriad of subtle adjustments and
> changes permitted with
> adjustment layers to 16 bit psd files, not to mention sending
> those files into the printer via RIP software such as Quadtone RIP
> and others, make a tremendous difference in control of the
> final print quality. In my opinion the only exception might be
> images shot in carefully lighted studio situations, where one
> can obtain perfect tonal, color and contrast values,
> directly into the
> RAW image exposure. And even then, I can think of
> more than one reason that one may want to make some post-RAW
> processing changes.
>
> So this brings us to the crux of the situation: WHY would you want
> to print directly from RAW if your purpose as a photographer
> is to produce the best possible quality? And while we're at it,
> could you let us know from where you obtained what seems to
> be, at best, theoretical information on RAW files, how they work,
> what they won't do, because IMHO, even if most of what you
> wrote is provable, in practical use, little of it holds water.
I agree, and I most certainly _wouldn't_ print without editing, not to
mention saving the edited version. In fact, I usually do lots of edits, way
beyond what you could ever do in any raw converter, then save my final
version as a quality 12 JPEG, since there's no need for more than eight bits
of resolution once you're ready to print. Indeed, printer drivers generally
only accept eight-bit data anyway, so obviously one would use curves and
other tools to extract the optimum range out of the larger raw data values.
Raw files are just that, "raw material".
My point was only to clarify that when you load a raw file into Photoshop,
you're not converting it to some other file format, you're only loading
image data into RAM where you can do what you want with it. The original
poster seemed to think that when you have an image open in Photoshop, it's
"in" some file format, when it's actually not in any file format at all,
because it's not in a file.
As to where I get my info on how raw files work, you can find data on the
web about Canon's raw format, and Adobe publishes a full DNG specification,
both of which I've studied.
--
Ciao, Paul D. DeRocco
Paul mailto:pderocco@...