Bucky wrote:
On Aug 18, 11:55 am, wrote:
I need some help in explaining the JPEG compression feature in
digital cameras. My camera (which likely is similar to most others)
has the feature to compress the photo JPEG files in the storage
card. It also has the choice to have different pixel sizes (example:
3000x2250, 2000x1500, 1024x768, etc). What is the difference of the
above two features?

Tough question. My theory is that, assuming that jpeg compression is
optimized, that file size will be be the determination of image
quality. So, if you are wondering which will have a better image
quality: medium resolution at max quality (lowest compression) vs max
resolution at med quality (med compression), I would guess that the
one with a larger file size.

Of course, you should also do a sanity check by viewing both files
resampled to the same resolution (with antialiasing). For example, to
your screen resolution (1024x768 or whatever).

What I have found in practice is that using the maximum resolution with
the "normal" quality setting can beat the lower resolution with the "fine"
quality setting. Of course, this is highly camera dependant, and you
should test for yourself.

My theory behind this is that running at the maximum resolution, you are
more limited by the MTF of the lens and other components, so there is
relatively less high-frequency component in the image, and that the JPEG
algorithm does not need to work so hard to compress the data, and can
therefore provide a higher quality image.

So my recommendation to the OP is to stick with maximum resolution (3000 x
2250), and to make a series of test photos at the different quality (JPEG
compression) levels, and see where you want to draw the line between file
size and image quality. Include both sharp edges and subtly coloured (or
even varying grey) areas in your test image. I have found that the
"normal" quality setting is satisfactory on the Nikon cameras I have
owned - your camera and image quality requirements may differ.

Nikon do seem to have the many parameters you can adjust in the JPEG
algorithm very well chosen.

Cheers,
David