Re: RAW images...

Floyd L. Davidson wrote:
"Joseph Meehan" <sligojoe_Spamno@xxxxxxxxxxx> wrote:
Floyd L. Davidson wrote:
"Joseph Meehan" <sligojoe_Spamno@xxxxxxxxxxx> wrote:
Floyd L. Davidson wrote:

You cannot resize it without adding serious artifacts from
reblocking pixels. Saved in any non-lossy format (RAW, TIFF,
PPM, etc.), and that is not a problem.

Can you offer an example where there was serious (noticeable)
reduction in the final product due to resizing to a smaller size
from a larger original jpeg?

Take *any* image in a RAW, TIFF, PPM or whatever format that has
a wide range of colors (i.e., not something with block graphics
using solid colors) and save it to JPEG format. Then save it
again to be 95% the size of the first image saved. Now open
that first JPEG image and scale it down to 95% of the size it
is. Compare the two.

There is your example!

The fun examples to do that with are those with a very fine
color pattern which appears in the original image as a smooth,
but odd shade of color that is not constant.

An out of focus wall in the background would be a good example.
It is quantized one way on the first JPEG save, and then that is
quantized with a different block size in the second save. That
will often result in a very visible pattern instead of a nice
smooth even color.

I asked for an actual real life example not a test of theory.

I would agree in theory you may well loose some quality under
certain conditions. However I believe we are talking about real life
general use results from properly exposited images.

Try it. You'll find that unless the block sizes are multiples,
*every* time you do that you produce the example you've asked
for. (The reason for choosing a 95% reduction was to virtually
eliminate the possibility of multiples in the block sizes.)

Which is to say, that in real life if you resave a JPEG, you
damage the image virtually *every* time.

I can't speak for everyone, but in my real life I don't make a habit of
repeatedly reducing my image size to 95%. In fact if I believe I will be
doing any repeated editing I would change to a lossless format. I would say
about 10% of my files are in RAW or TIFF. The rest just don't call for it.



(Note that I am *not* arguing that you should or should not
shoot RAW or JPEG. I'm just saying that when choosing one or
the other, there are serious consequences which need to be
considered. The above is not insignificant; but it is no more
or less significant than the requirements for post processing
that are implied with choosing RAW format.)

I guess our idea of serious and/or our opinions of the likelihood of a
problem differ.


--
Joseph Meehan

Dia duit


.

Relevant Pages

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  • Re: RAW images...
    ... Saved in any non-lossy format (RAW, TIFF, ... PPM, etc.), and that is not a problem. ... using solid colors) and save it to JPEG format. ...
    (rec.photo.digital)
  • Re: RAW or not RAW? :)
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