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07-05-2008, 12:05 AM   #16
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QuoteOriginally posted by ariahspam Quote
The PEF is LOSSLESSLY compressed, that means that it is compressed WITHOUT losing data, unlike lossy compression used in jpegs. Do some research on wiki.
I think there is no "lossyless" *compression* for image formats. If we compress image data, there must be some picture data dropped. Whether we can see much difference is another story.

07-05-2008, 12:17 AM   #17
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QuoteOriginally posted by RiceHigh Quote
I think there is no "lossyless" *compression* for image formats. If we compress image data, there must be some picture data dropped. Whether we can see much difference is another story.
So, your knowledge about variety of image compression formats seems to be not very advanced. Keep on learning...
07-05-2008, 02:27 AM   #18
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QuoteOriginally posted by jeggy Quote
So, your knowledge about variety of image compression formats seems to be not very advanced. Keep on learning...
No problem. I'll be glad to learn how compression can be achieved without dropping some of the original data, putting aside file packing, which is not about image compression (but file compression, as I stated only about image compression in my last reply). Please teach us. Thanks.
07-05-2008, 03:09 AM   #19
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I'll have a go at trying to explain lossless compression. Maybe it's done using Run-Length Encoding. As I understand RLE, if enough consecutive pixels are the same in a scan line, you can replace them with one instance of the value and a token indicating how long is the"run" of the same value, rather than just repeating the value. If I'm right, a picture of a single pure colour (assuming no noise elsewhere) would have the greatest compressibility, pure noise would have negative compressibility since the RLE overhead on top of a random source would increase the filesize rather than reduce it, and a typical photo would fall somewhere in between these two extremes.


Last edited by dosdan; 07-05-2008 at 03:30 AM.
07-05-2008, 03:20 AM   #20
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Interesting, thanks for sharing! n/t

There is no text.

QuoteOriginally posted by dosdan Quote
I'll have a go for lossless compression. Maybe it's done using Run-Length Encoding. As I understand RLE, if enough consecutive pixels are the same in a scan line, you can replace them with one instance of the value and a token indicating how long is the"run" of the same value, rather than just repeating the value. If I'm right, a picture of a single pure colour (assuming no noise elsewhere) would have the greatest compressibility, pure noise would have negative compressibity since the RLE overhead on top of a random source would increase the filesize rather than reduce it, and a typical photo would fall somewhere in between these two extremes.
07-05-2008, 03:38 AM   #21
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QuoteOriginally posted by RiceHigh Quote
Please teach us.
No problem.

You write "I think there is no "lossyless" *compression* for image formats".

The term is lossless. In essence, there are two cases to distinguish:
  • Content-aware data compression:
    1. Lossy compression as, for instance, JPEG, JPEG2000, MP3, H.264. All lossy compression algorithms start from a model of how a human would perceive the data. Which is why lossy compression doesn't exist for general data. Lossy compression algorithms are the most elaborate ones.
    2. Lossless compression as, for instance, FLAC, GIF, PNG, PEF, DNG, TIFF (sometimes only as an option). Typical compression rates are 50% here. For both, audio and image. Except TIFF-G4 for binary B&W (fax) which is lossless and more efficient.
  • Content-unaware data compression (aka generic data compression):
    1. Lossless compression as, for instance, ZIP, BZIP2 etc. Typical compression rates vary between 0% and 90% here. Typically best for text formats, esp. HTML and XML.
BTW, lossless means that a bit-identical copy of the original can be reconstructed.


So, compression only "looses data" if the compression was lossy. Not the case for PEF and DNG.

@RH, please give a short notice that you have been teached successfully. You know that I sometimes defend You. So now, please be kind enough to acknowledge some of the rare cases where you have been wrong. No human is perfect. Thank You.


Further reading: Lossless Image Compression Links

Last edited by falconeye; 07-05-2008 at 03:53 AM.
07-05-2008, 03:49 AM   #22
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QuoteOriginally posted by RiceHigh Quote
I think there is no "lossyless" *compression* for image formats. If we compress image data, there must be some picture data dropped. Whether we can see much difference is another story.
Ever heard of PNG compression ?
It's lossless.
Try and save an image with 16 bits per channel to a 16bit TIFF file and 16bit PNG file. Can you spot the size difference ? It's quite big you know.
Now unpack them, and subtract one from another. The result ? Completely black image (all pixels with values zero).
07-05-2008, 04:17 AM   #23
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QuoteOriginally posted by falconeye Quote
@RH, please give a short notice that you have been teached successfully. You know that I sometimes defend You. So now, please be kind enough to acknowledge some of the rare cases where you have been wrong. No human is perfect. Thank You.
I think whether I am right or wrong is really not (that) important BUT only the truth is important.

Also, thanks for the "rare cases" kind comment indeed. I would have thought that I have always been wrong as pointed out by particular people! ;-) (But again, I think it is yet mostly a don't care case for whether an individual is right or wrong)

QuoteQuote:
Thanks for the link.

07-05-2008, 04:20 AM   #24
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How about IF?

QuoteOriginally posted by procyon Quote
Ever heard of PNG compression ?
It's lossless.
Try and save an image with 16 bits per channel to a 16bit TIFF file and 16bit PNG file. Can you spot the size difference ? It's quite big you know.
Now unpack them, and subtract one from another. The result ? Completely black image (all pixels with values zero).
..IF you shoot a DNG and a PEF for the same (static) thing, convert to TIFF and subtract them?
07-05-2008, 04:26 AM   #25
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I use DNG for important shots mainly cause I use Photoshop and it's DNG plugin is fantastic. I haven't yet tried to figure out how to use PEF with Photoshop and as I don't like the Pentax processing software, I don't use PEF.

I will use jpeg for fun snapshots of the dog and such
07-05-2008, 04:32 AM   #26
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QuoteOriginally posted by RiceHigh Quote
..IF you shoot a DNG and a PEF for the same (static) thing, convert to TIFF and subtract them?
It would be nice to test it, but sadly quite impossible because of sensor noise, minor light fluctuations etc.
07-05-2008, 04:34 AM   #27
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QuoteOriginally posted by KrisK10D Quote
I use DNG for important shots mainly cause I use Photoshop and it's DNG plugin is fantastic. I haven't yet tried to figure out how to use PEF with Photoshop and as I don't like the Pentax processing software, I don't use PEF.
PEF opens in Photosop exactly like DNG. No figuring out needed. Same Camera RAW plugin is used. Same options are available. Same result.
07-05-2008, 05:04 AM   #28
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QuoteOriginally posted by RiceHigh Quote
I think whether I am right or wrong is really not (that) important BUT only the truth is important.
Being somebody who swore an oath on Truth to get his PhD ... it does matter!

Progress in science is based on falsification of assumptions and therefore, it IS important to acknowledge to have been wrong.

Sorry, RH, but I can't build you a bridge bigger than this. Say, "I stand corrected" and you'll see, it doesn't hurt

Last edited by falconeye; 07-05-2008 at 05:43 AM.
07-05-2008, 06:33 AM   #29
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QuoteOriginally posted by falconeye Quote
Being somebody who swore an oath on Truth to get his PhD ... it does matter!

Progress in science is based on falsification of assumptions and therefore, it IS important to acknowledge to have been wrong.

Sorry, RH, but I can't build you a bridge bigger than this. Say, "I stand corrected" and you'll see, it doesn't hurt
No problem. So, I admit that I have been wrong this time and I stand corrected! That's a forum is for afterall - friendly discussion to find out the truth (and for sharing as well). Of course it won't hurt in anyway, as long as we discuss on the topic and don't go personal :-)
07-05-2008, 07:13 AM   #30
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I use DNG primarily because I'm lazy. Currently I'm using PSE 3.0 and DNG coverter V 3.5 for my photo editing needs. I should upgrade to at least PSE 5.0 and a new version of DNG Converter, but I "haven't gotten around to it yet". Adobe DNG converter 3.5 doesn't recognise the PEF's from my K10D, so I use DNG, which I then convert to compressed DNG's using the Adobe converter, I save space that way on my hard drive and back up drives.

NaCl( "one of these days I'll upgrade"...I've been telling myself that for years now)H2O
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