added these comments in the current discussion du jour ...

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? If you
store a 3000x2250 pixel data in compressed mode, does it loose
its quality? Can it be re-instated to full uncompressed size
without loosing photo quality?. When I compressed the data, it
will fit more pictures in a single storage card. But, is it
the same if I choose 2000x1500 pixel and no compression
instead? Thanks for info.

Resolution is measured by horizontal and vertical pixels for an
image, the area of which constitutes mega pixels. JPEG
compression is how much or little the uncompressed data is made
smaller. Since JPEG is a so-called "lossy" format, it literally
throws away pixels in order to drastically shrink the file size.
The idea of the algorithm is to choose pixels to disgard that
have a mathmatical probability of not being noticed by the human
eye.

However, when compression begins to get even moderately high,
defects begin to appear, commonly called "JPEG artifacts",
artifact meaning "what is left behind". This can easily be seen
by blobs, streaks, blurry areas, minor destruction of fine
detail, and sometimes posterization.

"Better" digital cameras will give you choices as to how much to
compress for a given mega pixel image. Lots of words used but
"basic", "normal", and "fine" are common. I don't think any
cameras tell you the actually number they use nor the Chroma
subsampling they use, but under most circumstances, one can
quickly show themselves that "basic" is pretty awful, "normal"
MAY produce artifacts 5, 10, 15% of the time, and "fine" rarely
does.

However, many - not all - of the less expensive P & S cameras
only give you marketing BS like "good", "better" and "best", but
what they're really doing is maintaining the same JPEG
compression but upping the MP. The reason that so many lower cost
but high MP cameras do that is that they also want to advertise
how many pictures you can fit on even a small memory card.

I'm not sure about the rest of your question to exampand more on
my answer. Some cameras allow TIFF, which is lossless, and even
better cameras - certainly DSLRs - can also save in RAW.

Without starting another religious war, if you can get by with
JPEG and it fulfills what you want and need the camera to do for
you, you'll be just fine. It is universally readable, lots of
free or almost free editing apps as wells as commercial apps, and
you can save money on memory if that is a consideration.

But, since I know of NO camera buyer who isn't interested in the
best possible quality, I would look for cameras that offer a
choice of compression so that you can run some tests for yourself
and make up your own mind.

--
HP, aka Jerry