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08-02-2010, 05:48 AM   #1
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K-x JPEG Compression

I recently installed the software that came with the K-x. I rarely if ever work in RAW. But I have noticed that if you were to take the original JPEG out of the camera at about 5 megs a file on average, and load them into the software and save them at the lowest quality of "*"; you end up with a file that is approximately 1.5 megs. If you were to load both the orginal and the newly saved file and pixel peep till your eyes bled, you would not see a difference. My question is - what is the advantage of keeping the huge files?

08-02-2010, 05:53 AM   #2
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QuoteOriginally posted by Nightwings Quote
I recently installed the software that came with the K-x. I rarely if ever work in RAW. But I have noticed that if you were to take the original JPEG out of the camera at about 5 megs a file on average, and load them into the software and save them at the lowest quality of "*"; you end up with a file that is approximately 1.5 megs. If you were to load both the orginal and the newly saved file and pixel peep till your eyes bled, you would not see a difference. My question is - what is the advantage of keeping the huge files?
Have you tried printing the two to compare?
08-02-2010, 06:59 AM   #3
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Look for gradients:

https://www.pentaxforums.com/forums/digital-processing-software-printing/1092...-too-high.html
08-02-2010, 07:14 AM   #4
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If you know what to look for, it is not hard to see the compression artifacts caused by too low a quality setting. Do a web search for "jpeg compression" and look at sample images used to illutrate the articles you find.

08-02-2010, 10:14 AM   #5
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QuoteOriginally posted by Marc Sabatella Quote
If you know what to look for, it is not hard to see the compression artifacts caused by too low a quality setting. Do a web search for "jpeg compression" and look at sample images used to illutrate the articles you find.
I know that .. But try this:

Shoot at the highest quality level in your camera - leave it at default sharpening.

Open the image in Silkypix .... and save it back to the lowest setting ... one star.

Now use a viewer that will alow you to open two sessions ... I use VUEPRINT. Open each sample and zoom in to each section you want to study and ALT-TAB between the two. This will give you an exact-instant method of switching between the two. You'll not see the difference. But your 5+meg file will now be about 1.5meg.

Now having said that .... If you load the images into Photoshop, and save to lowest setting, yes you will see the difference, albeit small. But Silkypix? Nope.
08-02-2010, 10:55 AM   #6
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This link
http://regex.info/blog/lightroom-goodies/jpeg-quality
is excellent way of seeing (LightRoom's) JPG compression levels.

By clicking on the Lossless, selecting its radial button, and allowing the image to load - then just hover the mouse pointer over any JPG compression level, then pull the mouse pointer away downwards one can toggle between the chosen compression level and the lossless - this is a good way of making out the differences - sometimes at first look a particular compression level looks the same as the lossless - but when one pulls away downwards to re-display the lossless there is a slight change in the image - so ipso facto there is a "visible" difference - but whether that difference is significant or not, is up to the individual to decide if it's worth going up to the next lower compression level.

It was very educational to see that the shots with lots of obvious details didn't seem to make that much difference at first look - by using the the pull away method one can then see where the differences were more easily, and then one can concentrate on those areas.

The reed window shade was really interesting - at first look almost all the compression levels seemed acceptable - it was only by using the pull away method was I able to see the change and therefore the difference and even then by level 39-46 even the pull away method didn't seem to show much change and therefore difference.......

However as Eruditass has already pointed out it's the color gradients that JPG seems to affect - as in the sunset & bird photo - even without the pull away method - one can quite easily see the "banding" of gradient color at anything below the quality level 47-53 - at that level I can still see the banding - but it is kind of acceptable to my eyes - of course YMMV - and I could have claimed I could see it even at a much higher quality (lower compression) level - (which I actually can, since the pull away method gives pretty critical comparison) just to show what a critical eye I have (so what?!) but I just wanted to point out what was acceptable to me on my monitor.

One can download a copy of the lossless images and experiment in any editor saving at different JPG compression levels to see what is acceptable - if possible try to overlay any compression over the lossless to do any more critical A-B comparison - I find I need that sometimes just to id where to concentrate on.....
08-02-2010, 11:16 AM   #7
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QuoteOriginally posted by Nightwings Quote
Shoot at the highest quality level in your camera - leave it at default sharpening.

Open the image in Silkypix .... and save it back to the lowest setting ... one star.
I don't have silkypix, but if you want to post a 5MB and 1.5MB version of the same image somewhere, I guarantee I'll bee able to show you the artifacts in the 1.5MB version. Silkypix isn't magic. The JPEG compression algorithms don't differ much between applications; in order to get that kind of compression, there *will* be artifacts. But if they're not big enough to be noticeable to you, great!
08-02-2010, 12:34 PM   #8
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Generally JPG compression is usually very hard on Red -
here's an illustration -
using the logo from a Red Swiss Army knife -

left is saved with PS Elements 7.0 high quality JPG (PSE=10)
and the second (middle) is lower quality (PSE=4)
I also added the third JPG saved in PhotoImpact 8 (my usual editor) saved at 75% which is usually of pretty good/presentable quality - but as one can see in the third crop PI's JPG engine is not particularly good in preserving Red details -


The physical file sizes
PSE=10 - 6.06Kb
PSE=4 - 3.19Kb
PI=75% - 3.75Kb

08-02-2010, 04:19 PM   #9
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JPG compression is hard on Red and Blue -
I just postd #123 in the thread: Modern LED Stage Lighting & photography problems - where I was outlining the the problems encountered when presenting/posting a photo for the web - one has to use JPG and therefore face the compression dilemma.

Since it seems very appropriate I'll paste it here -

JPG compression can play quite significantly in how the photo is presented -
as seen in the opening post #1 of the thread: Modern LED Stage Lighting & photography problems.

I did an experiment to demonstrate this a bit more objectively and consistently.

Opened a new image filled half with black and the remaining white.
Then typed in the main colors of my photo editor (PhotoImpact 8) in each half and saved it as a PNG which is lossless.
(for some reason PhotoBucket will no longer upload TIFF images):



Using my usual JPG compression level PI=70 (11Kb)

we can see degradation in the Magenta -
due to the degradation in Red and Blue.

Even at PI=100 (highest quality) (34Kb) there is degradation in the loss of vividness in the Red and Blue -


PS Elements seems to fare much better -
PSE = 10 (12 is the highest quality) (28Kb)


But if we picked a file size that is similar to the PI=70 images above -
it's between PSE=2 (15.4Kb)

and PSE=1 (10.6Kb) the lowest quality level!


So we can see that the "Quality" scale for the JPG compression bears no resemblance to each other between PhotoImpact 8 and PS Elements 7.0 -
however PS Elements 7.0 is much more recent than my old version of PhotoImpact 8 (circa 2002) and I would expect that Elements 7.0 should have a better JPG engine and it does seem that way

However even PSE=6 (18Kb) is not that great -


It is only by about PSE=7 (22.6Kb) that the image jumps to a better quality -
(which PhotoImpact's JPG compression did not attain even at its highest quality)

Last edited by UnknownVT; 08-11-2010 at 11:48 AM. Reason: improved images
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