What program is best at JPEG compression?

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

Until I started reading posts in this thread, I was unaware
that there are ANY programs that can alter a JPEG without
having to recompress the entire image. I can see your point
about a localized change like the small parts of an image
that had red eye removed, but I would think that you are
right that any change that affects literally every pixel in
the image, which would happen in your example of changing
colors, would require a

So I guess you know that Irfanview, among other applications,
can do lossless rotation and flip, although it truncates to
8-pixel boundaries so it's only truly lossless with 8x pixel
dimensions.

All good apps can do lossless rotation, in 90 degree increments.
If Irfanview can do an arbitrary rotation losslessly, I'm not
aware of it, Bill. Which did you mean? PSP 9 can also do a
lossless rotation, but I rarely use it because I've never been
able to see any difference between lossless and ordinary 90 deg
rotates. But, in my quote above, I concurred with another person
that a global color change would alter the entire bitmap
requiring a full recompress.

To guess JPEG parameters, you can obtain the "jpegdump"
program by Allan N. Hessenflow. When saving an edited JPEG,
the destruction is minimal if you save with the same quality
and chroma subsampling.

Thanks for the heads up. Over some 13 or 14 years of JPEG
experience, I have adopted my own norms for best first guess at
the right compression and Chroma subsampling settings based on my
visual evaluation of the complexity and type of image. But, I
don't trust to judgement and experience, I look at the compress
and saved image to verify that no damage occurred. In my case, I
can see damage, I would say about 2% of the time, so I alter the
settings until it goes away.

As the JPEG FAQ says, destruction is worst when resaving with
slightly different parameters at the higher quality values,
counterintuitively.

P.S. Thanks for your comments in the PaintShopPro thread.

Mine about DCNR? If yes, you're welcome. As to the JPEG FAQ,
can't speak to that. I understand it conceptually but not at all
in a way I can use the knowledge in a practical example.

--
HP, aka Jerry

In article ,
HEMI-Powered wrote:
Mike S. added these comments in the current discussion du jour
...


In article ,
HEMI-Powered wrote:

Until I started reading posts in this thread, I was unaware
that there are ANY programs that can alter a JPEG without
having to recompress the entire image. I can see your point
about a localized change like the small parts of an image that
had red eye removed, but I would think that you are right that
any change that affects literally every pixel in the image,
which would happen in your example of changing colors, would
require a complete recompress.

Well, they _claim_ that they do so, but I have not been
obsessive enough to try to verify it. Conceptually, though, I
don't understand how Huffman encoding would even allow you to
change _any_ pixel values in a bitmap and not have it require
changing the rest of the compressed data.

That's what I always thought, until I read about these magic
programs in this thread. I'm no expert and not interested in
trying to verify the veracity of the claims because my work isn't
such that would be helped. But, in keeping with my general
philosophy that learning is a life-long endeavor, if somebody has
invented a better mouse trap, I'm interested enough to at least
listem.

JPEG Wizard's claims for lossless processing are quite clear.
Photoline 32 suffers from poor translation from German, both on their web
site and the help files. A strict reading would suggest that only crop and
rotate functions are lossless, which is not a unique achievement. But they
talk about changed and unchanged "JPEG data" which probably means
something more exact in the original German.

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

That's what I always thought, until I read about these magic
programs in this thread. I'm no expert and not interested in
trying to verify the veracity of the claims because my work
isn't such that would be helped. But, in keeping with my
general philosophy that learning is a life-long endeavor, if
somebody has invented a better mouse trap, I'm interested
enough to at least listem.

JPEG Wizard's claims for lossless processing are quite clear.
Photoline 32 suffers from poor translation from German, both
on their web site and the help files. A strict reading would
suggest that only crop and rotate functions are lossless,
which is not a unique achievement. But they talk about changed
and unchanged "JPEG data" which probably means something more
exact in the original German.

Mike, sorry to still be dense, but is the rotate general or in 90
deg increments? The latter is easily done, I'm no mathemetician
but I can't imagine moving all those pixels/bytes around an
arbitrary number of degrees without destroying the compression
scheme that must get load in along with EXIF and the actual
image. I can visualize crop being lossless, however, IF it runs
along 8x8 and/or 16x16 pixel boundaries that are the foundation
of JPEG's compression algorithm. Again, I'm neither a
mathemetician or a JPEG guru so I could be entirely all wet here.

Again, guys, this has been an interesting thread to kinda just
look in on. The entire notion of a lossy compression scheme like
JPEG and the math background I do have from engineering school 40
years ago tells me that to take all the compressed gobbledegook
that's in the file, uncompress it to even to a rotate or crop,
then save some of it back without messing up even one other pixel
seems like magic and a dream come true.

Thanks for the background.

--
HP, aka Jerry

Fed-Up-With-Corel added these comments in the current discussion
du jour ...

AFAIK only on selective compression areas, or limited area
processing such as red-eye removal. Then again, it really
isn't an editor, per se; more of an image manipulator and
processor. I'd imagine if you were to make any global change,
such as color balance adjustment, that would require
reprocessing in order to save the modified image.

Correct. If you do a global change then yes, the whole image
would have to be ran through the JPEG routine again. The
upside is that when using "Save" (not "Save-As") the same
compression level that was used on the original will still be
applied to the result without you having to guess or do a
thing.

Isn't using Save vs. Save As inherently dangerous? If anything at
all goes bump in the night during the (re)Save, your original is
lost forever. I would imagine that it would be a damn good idea
to copy your file(s) to a temp folder just in case.

Often I only need to use the clone-tool to remove a
small fence-line or power-wire. Or its "Repairing Brush" (same
as a healing-brush) to remove a few harsh lines in a face.
Maybe get rid of that erroneous spot in the sky or defect in a
flower petal, or add a small bit of text for documentation.
Why recompress the whole image for that? PhotoLine 32's
authors found a way around the image degradation caused by
re-saves of JPG data. There are times that, as meticulous as I
am to always work off of copies of the original, that on rare
occasions when in a hurry I realize that I accidentally saved
my edited and downsized work over the original.

That's the danger I was talking about, but instead of
inadvertantly overwriting the old file, you'd be doing it
intentionally. Seems naive on my part, maybe, but that seems like
an invitation for a visit from Murphy.

After that
wave of fear and anguish washes over me then I remember, "Oh,
I'm using PL32. No harm done." I just undo all my edits and
save the original again. Hit redo a few times to get back to
where I was (or use the Undo-List for all this if there are
many edits), and save my edited image under a different name
or folder as I originally intended. Not a thing harmed to the
original. Just as if it came right from the camera. You can't
do that with any other advanced image editor on the planet.

In my normal processing, before I'm finished with a picture, I
will do a Save, not Save As, periodically and especially before I
do something really drastic in case the Undo function fails or,
in PSP 9's case, something higher up in the History Pallette
fails and all is lost. But, if I'm about to do some serious
experimentation to go in a couple of directions to see what works
best on a complicated edit, I'll do a Save As to a different file
name for safety. If you're a PSP user, you'll understand why my
real standard "save" function is the JPEG Optimizer because it
gives me not only easy access to Chroma subsampling, but a real-
time finished file size in full bytes, not KB, which I find
indespensible in judging how much to compress a given image,
based on long past experience.

Please realize that I'm hardly refuting anything you or anyone is
saying, I'm just asking questions and commenting on what I've
personally seen and done. All this stuff that has been
transpiring in this thread is fascinating to me, even if I never
acquire any of the software.

--
HP, aka Jerry

On Jul 24, 5:48 pm, "HEMI-Powered" wrote:
....
All good apps can do lossless rotation, in 90 degree increments.
If Irfanview can do an arbitrary rotation losslessly, I'm not
aware of it, Bill. ...

Irfanview only offers the following losslessly:

Flip horizontally or vertically.
Rotate 90, 180, or 270 degrees.

It works as you expect.

Alan

In rec.photo.digital HEMI-Powered wrote:

All good apps can do lossless rotation, in 90 degree increments.
If Irfanview can do an arbitrary rotation losslessly, I'm not
aware of it, Bill. Which did you mean?

Yes, Irfanview does 90/180/270 degrees, or vertical/horizontal flip.
Just like PSP, apparently. (I have PSP 9 but don't use it much.)

It's not really lossless, because most images are not evenly divisible
by 8 in both directions, so "lossless" rotation usually trims off
some pixels rows or columns on the bottom or right side.

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

On Jul 24, 5:48 pm, "HEMI-Powered" wrote:
...
All good apps can do lossless rotation, in 90 degree
increments. If Irfanview can do an arbitrary rotation
losslessly, I'm not aware of it, Bill. ...

Irfanview only offers the following losslessly:

Flip horizontally or vertically.
Rotate 90, 180, or 270 degrees.

It works as you expect.

That's what I thought, Alan. Most/all "good" graphis programs work
that way because, if I have my limited JPEG technical spec
knowledge right, a rotation like you describe can be done by
setting a switch in the file to tell whatever is trying to
open/view it to do the flip, mirror, or 90 deg rotates.

--
HP, aka Jerry

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

In rec.photo.digital HEMI-Powered wrote:

All good apps can do lossless rotation, in 90 degree
increments. If Irfanview can do an arbitrary rotation
losslessly, I'm not aware of it, Bill. Which did you mean?

Yes, Irfanview does 90/180/270 degrees, or vertical/horizontal
flip. Just like PSP, apparently. (I have PSP 9 but don't use
it much.)

Interesting, I have Irfanview but have never installed it!

It's not really lossless, because most images are not evenly
divisible by 8 in both directions, so "lossless" rotation
usually trims off some pixels rows or columns on the bottom or
right side.

As I said earlier, I don't use the lossless rotate of PSP 9 so I
don't know if it does or doesn't clip pixels but your logic
strongly suggests that any real implementation of the JPEG
standard would probably suffer from that.

In my hobby of car pictures, if I can, I include about 20-25%
space all the way around the car so I can crop for best
composition in PSP 9. Of course, it helps a whole lot to do the
basic compose at the time I shoot the pictures grin but I'm
generally so pressed for time that I try to take advantage of
either 4 mega pixels (usually) or 8 MP having more than enough
pixels so that I can do a major crop and still not drop below the
larges size I generally save to, 1600 x 1200. So, all that is to
say that if PSP 9 were clipping edge pixels at all, I'd likely
not notice it.

BTW, you've said 8x8 a couple of times. Excuse my ignorance
again, but I thought that the JPEG spec allowed both 8x8 and
16x16 blocks to be considered when deciding which pixels to throw
away. Or, am I mixing this up with something else? If I am right,
I have no idea if an image could have both block sizes in the
same file or not.

As I said, my math knowledge is what I needed to learn in
engineering school a long time ago, so I just fly by the seat of
my pants on all these quality issues and judge by eye. Naturally,
I DO zoom in and out and such and I DO look for obvious problems
like aliasing, and I DO look for JPEG artifacts after I save but
before I blow the in-memory bitmap away.

--
HP, aka Jerry

James Silverton wrote:
Matt wrote on Tue, 24 Jul 2007 14:46:19 GMT:

MI David J Taylor wrote:
?? imbsysop wrote:
?? [] I've always thought jpeg and its compression algorithm
?? were subject to
?? a general standard and not to any program makers' fantasy
?? ..????
??
?? There is a standard, but with a large number of different
?? choices. For example, you can change the colour
?? resolution relative to the luminance resolution. How
?? different programmers interpret "95% quality" is up to
?? them, so it's entirely possible that different programs
?? will better suit different images.

It is an interesting question as to which is the best general method
since *most* people won't want to use more than one technique. It does
beg the question of what is wanted. Is the "best" method that which
produces the smallest result or some sort of compromise among size,
resolution and color resolution etc.?

Also a good point - what comprises the "best" compression is entirely
subjective. Only way to really answer the question is for a person to
try the options for him/herself, and decide what works best for him/her.

In article ,
HEMI-Powered wrote:
Mike S. added these comments in the current discussion du jour
...

That's what I always thought, until I read about these magic
programs in this thread. I'm no expert and not interested in
trying to verify the veracity of the claims because my work
isn't such that would be helped. But, in keeping with my
general philosophy that learning is a life-long endeavor, if
somebody has invented a better mouse trap, I'm interested
enough to at least listem.

JPEG Wizard's claims for lossless processing are quite clear.
Photoline 32 suffers from poor translation from German, both
on their web site and the help files. A strict reading would
suggest that only crop and rotate functions are lossless,
which is not a unique achievement. But they talk about changed
and unchanged "JPEG data" which probably means something more
exact in the original German.

Mike, sorry to still be dense, but is the rotate general or in 90
deg increments?

It's in 90 degree increments as you would suspect.