"Thorsten Froehlich" <nomail@nomail> wrote:

>
> You do realise that it is pointless to add some arbitrary number to an image
> file? Apart from the fact that misc image formats, JPEG included, don't have a
> standard DPI flag?

I do see your point. I think the OP was curious if (to paraphrase him) POV-Ray
could output its image renders at, say, 300 dpi, for printing purposes. (I guess
that would mean an 'embedded' 300 dpi setting... which is necessarily different
from the on-screen resolution of the render, which itself depends on the screen
resolution of the monitor its viewed on.)

When I take a JPEG or PNG image to a printing house nearby, they always specify
that it be at 300 dpi resolution-- regardless of the actual pixel size of the
image-- simply because the printing equipment is made to work that way, I
suppose. Currently, I have to do that in Photoshop, as a post-processing step
(with *any* image, not just POV-Ray's, as most images seem to have been created
with a default rez of 72dpi-- if 'default' is the right word.) Having a choice
of an actual *embedded* resolution in a POV image would be useful for that, if
only just to save a step.

But since Photoshop *can* convert a JPEG image from 72dpi to 300dpi (and the
printing shop's machines can 'see' it that way), doesn't this imply that JPEG
images can have an embedded resolution?

In any case, your comments have given me food for thought, about something that
seems like a curious paradox: A typical POV-Ray rendered image has NO stated
resolution info, just the width and height in pixels. However, when I take a
digital JPEG photo with my Canon Powershot camera, and take a look at the
image's 'properties' before any image-editing has been done to it at all, it
actually does state that the image already has a resolution of '180 dpi.' I had
always assumed this to be an actual 'embedded' resolution. Or is it simply
*metadata* that my particular camera has written to the file-- without any real
practical meaning? (With the exception being, how LARGE the image initially
appears in a particular image viewing/editing app like Photoshop, which has a
default resolution of 72 dpi... the size depending on the MONITOR'S own
resolution, of course.)

Although 'resolution' of an image may not be of practical concern most of the
time, it does have some importance.

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