[Digikam-users] Re: need advice re: format conversion

[Sebastian Schubert]

Hi,

I suppose you mix up something. crw and dng are RAW files, ie, they
include the full information from your camera's sensor (that's why
they are so big). A real picture in the sense of a jpg, png etc has to
be calculated from that. There is (a) no one to one correspondence,
ie, there are different approaches how to do that, different algorithm
and (b) you loose information on the way (which is not bad or better,
necessary, because you want to look at the picture). So there is no
way to get a RAW from jpg (well, I guess you could somehow get a raw
by guessing some data but that would not make any sense).

On Tue, Jan 18, 2011 at 5:41 AM, Tom Cloyd <tomcloyd at comcast.net> wrote:
> I find that converting the CRW to DNG is easy, but the resulting image
> (preview, at least) is washed out, and thus not good for previewing to
> decide about image quality relative to the possibility of doing further
> work on an image. Is there a way to get a better preview image for the
> DNG conversion?

Why do you want to convert them to dng? Just keep in mind, that there
are some raw converters which cannot work with dng. The preview of the
dng might look washed out because the preview might be calculated from
the raw itself, while the native canon raws include a preview jpg made
by the camera, where contrast is increased and sharpening is applied.
This does not mean raw is bad, you just have to make sure, that some
post-processing is applied.

>
> With the *.JPG originals, I find no advice in the manual. Should I just
> store the original JPG? If I convert to PNG, I get huge files, and my
> storage costs go up. I'd convert to DNG but I don't see how to do this
> in Digikam (yet). Is this even [a] advisable - for long term storage,
> and [b] possible, as a batch conversion in Digikam?

Why do you want to convert? First it's not possible to convert to dng
because of the reasons mentioned above. jpg is a lossy format. In
principle, if you open the jpg FOR EDITING (not for viewing) and save
it to another file, you loose information. By repeating that, you
loose more and more information (bad). On the other hand, png is
lossless compression. You don't loose information when saving it. So
if you plan to edit the jpg severals time, than a conversion to png
and then editing them might a good idea. However, if you have the raw
of the picture, I would work with the raw, because it's much more
flexible. The result can then be saved in a jpg (for viewing, that's
fine if you take a good enough jpg quality).

I hope that helps,
Sebastian