JPEG compression

My camera has various JPEG compression modes. The manual says that
higher compression means lower image quality, but I haven't seen any
difference in the image quality of the two compression levels that I
have been using: FINE (1:4) and NORMAL (1:8). However, I did see a
signigicant difference in file size. What am I missing here?

thanks

James Ramaley wrote:
My camera has various JPEG compression modes. The manual says that
higher compression means lower image quality, but I haven't seen any
difference in the image quality of the two compression levels that I
have been using: FINE (1:4) and NORMAL (1:8). However, I did see a
signigicant difference in file size. What am I missing here?

thanks

Best option to see the difference is to shoot some text and see it - but
usually you'll have to look it magnified, to see the difference.
There's distortion around text. But i agree that there's barely noticeable
difference between fine and normal, there's a bit more between normal and
coarse(or low, whatever your camera says).
Interesting point is that cameras use exactly opposite of usual words -
usually it's said High as high compression (and so low quality), while all
cameras have high as high quality...

More noticeable on straight edges and fine detail - signs, textures etc.
Zoom in enough and you'll see the difference, but at 'normal' scales it's
probably so minor a difference as to be negligible. Maybe becomes more
noticeable if you have to lift the shadows too...

Cheers, Jason (remove ... to reply)
Video & Gaming: http://gadgetaus.com

More noticeable on straight edges and fine detail - signs, textures etc.
Zoom in enough and you'll see the difference, but at 'normal' scales it's
probably so minor a difference as to be negligible. Maybe becomes more
noticeable if you have to lift the shadows too...

Cheers, Jason (remove ... to reply)
Video & Gaming: http://gadgetaus.com

More noticeable on straight edges and fine detail - signs, textures etc.
Zoom in enough and you'll see the difference, but at 'normal' scales it's
probably so minor a difference as to be negligible. Maybe becomes more
noticeable if you have to lift the shadows too...

Cheers, Jason (remove ... to reply)
Video & Gaming: http://gadgetaus.com

James Ramaley wrote:
My camera has various JPEG compression modes. The manual says that
higher compression means lower image quality, but I haven't seen any
difference in the image quality of the two compression levels that I
have been using: FINE (1:4) and NORMAL (1:8). However, I did see a
signigicant difference in file size. What am I missing here?

thanks

There are differences, but you might not be aware of them in any single
photo. Try compressing a picture of your lawn at both compressions
levels, and then compare them blown up onscreen to 200%. That should
show you how they are different, and what effect excess JPEG compression
has on the image quality.

James Ramaley wrote:
My camera has various JPEG compression modes. The manual says that
higher compression means lower image quality, but I haven't seen any
difference in the image quality of the two compression levels that I
have been using: FINE (1:4) and NORMAL (1:8). However, I did see a
signigicant difference in file size. What am I missing here?

thanks

There are differences, but you might not be aware of them in any single
photo. Try compressing a picture of your lawn at both compressions
levels, and then compare them blown up onscreen to 200%. That should
show you how they are different, and what effect excess JPEG compression
has on the image quality.

On 24 Oct 2004 22:30:16 -0700, (James Ramaley)
wrote:

My camera has various JPEG compression modes. The manual says that
higher compression means lower image quality, but I haven't seen any
difference in the image quality of the two compression levels that I
have been using: FINE (1:4) and NORMAL (1:8). However, I did see a
signigicant difference in file size. What am I missing here?

It all depends on what size your viewing at. Zoom in on the image,
and you'll soon see.

(James Ramaley) writes:
My camera has various JPEG compression modes. The manual says that
higher compression means lower image quality, but I haven't seen any
difference in the image quality of the two compression levels that I
have been using: FINE (1:4) and NORMAL (1:8). However, I did see a
signigicant difference in file size. What am I missing here?

Try shooting a high-contrast subject, like bare tree branches against an
overcast sky. Then look at the images at 100%. You'll probably see
some artifacts along the boundary between tree branch and sky in all
of the images, even the highest-quality one. In most photos, the effect
is less visible because the contrast is less, but now that you know what
to look for you'll see it in other places.

I did this once with my G2, and decided that memory cards and CDRs (for
archiving) are cheap, so I always shoot in either RAW (no lossy
compression at all), or JPEG at maximum size and least compression
(Superfine). I've never used the higher-compression JPEG modes except
for these tests.

Dave

(James Ramaley) writes:
My camera has various JPEG compression modes. The manual says that
higher compression means lower image quality, but I haven't seen any
difference in the image quality of the two compression levels that I
have been using: FINE (1:4) and NORMAL (1:8). However, I did see a
signigicant difference in file size. What am I missing here?

Try shooting a high-contrast subject, like bare tree branches against an
overcast sky. Then look at the images at 100%. You'll probably see
some artifacts along the boundary between tree branch and sky in all
of the images, even the highest-quality one. In most photos, the effect
is less visible because the contrast is less, but now that you know what
to look for you'll see it in other places.

I did this once with my G2, and decided that memory cards and CDRs (for
archiving) are cheap, so I always shoot in either RAW (no lossy
compression at all), or JPEG at maximum size and least compression
(Superfine). I've never used the higher-compression JPEG modes except
for these tests.

Dave