Compression in JPEG files in digital cameras

Thomas T. Veldhouse added these comments in the current
discussion du jour ...

HEMI-Powered wrote:

This is a fair statement and I respect you for recognizing
that not everone can be a superstar. I also appreciate some
corroboration that it is indeed some sort of "advanced"
individual who makes the jump from ordinary JPEG to 16-bit or
to RAW.


Oh ... for God's sake, it was SARCASM.

tell you what, save your sarcasm for somebody else, I don't like
it. when I reply to you or Wolfgang or any of those I call
"elitists", "theorists", or even "image bigots", it is because
THEY, and not me, are attempting to impose their will on me or
someone else. I don't think that is polite, just, or appropriate
behavior especially when so much of what gets discussed his is
pretty murkey at times.

And, I can see that I have to say EOT to you also.

--
HP, aka Jerry

"Thomas T. Veldhouse" wrote:

HEMI-Powered wrote:
OK, but again, Thomas, I interpreted the OP as being a fairly new
digital owner and thus a novice on file types, so I just
mentioned TIFF as an alternative if their camera supports it.
TIFF is universally recognized, although news readers cannot
decode it in line, and about its only drawback other than large
size is that if you want to save EXIF, you cannot use LZW
compression, or at least AFAIK.


Hardly any cameras support TIFF. Yes, you can use EXIF with LZW ... the are
completely unrelated as far as TIFF is concerned.

heavily edited, for brevity

Hello, Thomas:

Oh, then, I'm so very lucky that my Kodak P850 can do both TIFF and
RAW, in addition to JPEG. g


Cordially,
John Turco

HEMI-Powered wrote:

HEMI, could you please post an impage where you can easily see
JPEG artifacts at the highest quality your Rebel produces?
The reason I ask is, it's hard for me to see JPEG artifacts at
Q 95 and 1x1 or 2x1 chroma subsampling.

Incidently, I don't think I ever said I've seen an artifact in my
Rebel's higher of its two available quality settings. What I said
was that some significant percentage at the lower setting DID
exhibit artifacts.

OK, thanks. This kind of supports my assertion (on another thread)
that the initial JPEG encoding imposes little lossage on an image
other than what the Bayer-pattern sensor has already imposed.

As to Chroma subsampling, my normal setting is 1x2. I will lower
the compression number and/or change to 1x1 (none) until I can
eliminate the damage as described above.

It probably does no good, and might actually harm your image, to
switch from 2x1 chroma subsampling to 1x1. (I trust your Rebel
is writing 2x1, not 1x1.)

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

HEMI, could you please post an impage where you can easily
see JPEG artifacts at the highest quality your Rebel
produces? The reason I ask is, it's hard for me to see JPEG
artifacts at Q 95 and 1x1 or 2x1 chroma subsampling.

Incidently, I don't think I ever said I've seen an artifact
in my Rebel's higher of its two available quality settings.
What I said was that some significant percentage at the lower
setting DID exhibit artifacts.

OK, thanks. This kind of supports my assertion (on another
thread) that the initial JPEG encoding imposes little lossage
on an image other than what the Bayer-pattern sensor has
already imposed.

My experience with now the 3rd of my digitals - 1st two were EVFs
- is that your assertion is right, IF you choose the best quality
at a given mega pixels, i.e., lowest compression.

As to Chroma subsampling, my normal setting is 1x2. I will
lower the compression number and/or change to 1x1 (none)
until I can eliminate the damage as described above.

It probably does no good, and might actually harm your image,
to switch from 2x1 chroma subsampling to 1x1. (I trust your
Rebel is writing 2x1, not 1x1.)

I'm told that my Rebel writes to 2x1, I was talking about what
/I/ choose when I am post-procesing in PSP 9. Each step down the
scale makes the file size smaller and presumeably the image a
little worse. I have found that 1x2 is a very good compromise for
me. You may find that 2x1 works fine. But, as I said, if I cannot
fix the artifacts by lowering compression, I will go to 1x1, that
almost always takes care of them.

--
HP, aka Jerry

HEMI-Powered wrote:

I'm told that my Rebel writes to 2x1, I was talking about what
/I/ choose when I am post-procesing in PSP 9. Each step down the
scale makes the file size smaller and presumeably the image a
little worse. I have found that 1x2 is a very good compromise for
me. You may find that 2x1 works fine. But, as I said, if I cannot
fix the artifacts by lowering compression, I will go to 1x1, that
almost always takes care of them.

The JPEG FAQ warns that JPEG files should be saved at the same
compression settings as before, otherwise artifacts are magnified.
I'm not sure if this is also true of chroma subsampling...

John Turco wrote:

Hardly any cameras support TIFF. Yes, you can use EXIF with LZW ... the are
completely unrelated as far as TIFF is concerned.

heavily edited, for brevity

Hello, Thomas:

Oh, then, I'm so very lucky that my Kodak P850 can do both TIFF and
RAW, in addition to JPEG. g


I didn't say NO cameras use TIFF. Most that suppot RAW do not, but obviously
many do. I am not sure why one would want to shoot TIFF in camera though [as
opposed to RAW] unless they simply don't want to use the RAW converson tools.
I think I saw recently that the upcoming Nikon D3 will still suppport TIFF.

--
Thomas T. Veldhouse

We have more to fear from the bungling of the incompetent than from the
machinations of the wicked.

"Thomas T. Veldhouse" wrote:

John Turco wrote:

Hardly any cameras support TIFF. Yes, you can use EXIF with LZW ... the are
completely unrelated as far as TIFF is concerned.

heavily edited, for brevity

Hello, Thomas:

Oh, then, I'm so very lucky that my Kodak P850 can do both TIFF and
RAW, in addition to JPEG. g


I didn't say NO cameras use TIFF.

Hello, Thomas:

I was quite aware of what you said; didn't you notice the smiley, after
my sentence?

Most that suppot RAW do not, but obviously many do. I am not sure why one
would want to shoot TIFF in camera though [as opposed to RAW] unless they
simply don't want to use the RAW converson tools. I think I saw recently
that the upcoming Nikon D3 will still suppport TIFF.

"Hardly any cameras support TIFF." Which seems to contradict your later
statement - "but obviously many do" - no?

Regardless, I agree with your RAW-versus-TIFF remark. I've only toyed
with those modes, briefly, and saw that the P850's RAW files averaged
around 9GB, but the TIFF's were all precisely 14,821KB.

By contrast, this digicam's largest JPEG images have been about 3.2GB,
with the vast majority under 3GB (all the way down to 538KB).


Cordially,
John Turco

John Turco wrote:

"Hardly any cameras support TIFF." Which seems to contradict your later
statement - "but obviously many do" - no?


No it doesn't. Most cameras do NOT support TIFF. Many cameras support RAW.

Regardless, I agree with your RAW-versus-TIFF remark. I've only toyed
with those modes, briefly, and saw that the P850's RAW files averaged
around 9GB, but the TIFF's were all precisely 14,821KB.


Indicating a lack of compression and fixed length metadata (to the nearest KB
anyway).

By contrast, this digicam's largest JPEG images have been about 3.2GB,
with the vast majority under 3GB (all the way down to 538KB).


Funny ... my D200 supports JPEG and several modes right along side RAW.
However, I have never shot a single JPEG with this camera, so I can not tell
you how big the files are ;-)

--
Thomas T. Veldhouse

We have more to fear from the bungling of the incompetent than from the
machinations of the wicked.

Floyd L. Davidson wrote:

JPEG is a lossy form of saving the picture -

The Bayer sensor is already lossy, having only one of RGGB at
any of four pixel locations, so one could make the argument that
JPEG imposes no further loss.

You could argue that until you are blue in the face

If you shot using raw you'd have a better chance of correcting it.

Daniele