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07-21-2007, 01:13 PM   #16
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Nothings being lost, it is using a form of lossless compression to reduce the filesize. In music they do the same thing with formats such as OGG Vorbis, Ape, FLAC and Apple Lossless just to name a few. In audio a standard CD song may be 75MB in a pure WAV format but by using compression it becomes more portable in size around 10-15mb with no loss in the original untouched sound quality.

07-21-2007, 02:08 PM   #17
hamsi
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Entropy, c.r.brown, thank you for your quick responses.
when I unzip the compressed files by "winzip" or "winrar" they are same size again, not smaller. So I expect to get same size DNGs after converting from PEF. (I think "the size of in camera DNGs" should be equal to "the size of DNGs converted from PEF" since they are both the same format). That's why I'm surprised...
I assume that PEF is a lossless compression; while DNGs converted from PEF and in camera DNGs are both uncompressed.
I think if PEF were a lossless compression, DNG's converted from PEF wouldn't be smaller than in-camera DNG's. Where am I wrong?

I wonder if there is a test can prove that "PEF" and "DNGs converted from PEF" are both lossless as "in-camera DNGs"?
...seeing is believing...

Last edited by hamsi; 07-21-2007 at 02:25 PM.
07-21-2007, 04:22 PM   #18
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Whoa there folks.......now let's just hold onto our darned horses for a minute ! I simply can't resist disagreeing diametrically with c.r.brown's sweeping statement, when he casually states that:
Quote: "Nothing's being lost, it is using a form of lossless compression to reduce the filesize.........with no loss in the original untouched sound quality". I'm afraid that it's a commonly held misconception that when audio is converted to an Mp3 format, the "original sound quality" somehow remains magically "untouched". Although you are undoubtedly entitled to your opinion, I can categorically assure you that the reason for compressing audio files has nothing whatsoever to do with preserving "original untouched sound quality" ! The sole purpose of this compression process is to facilitate the reduction and subsequent transfer of digital data in order to store it on an MP3 player, computer hard disk or mobile phone etc. Something has indeed been lost in the data compression process and any discerning audiophile or competent sound engineer 'worth their salt' should easily be able to hear the difference between a track selected from a top-quality music CD and a compressed MP3 file of it. The widespread acceptance of mediocre portable multimedia devices doesn't alter this fact. I believe the EARS have it m 'Lord !!
This is probably not a very good analogy, but suppose for one moment that I am a vineyard owner and kindly invite you over one evening to partake of a particularly fine vintage claret. In order to elicit an unbiased opinion from you, I request that you put on a blindfold. Unknown to you however, I slowly begin diluting each glass with a small amount of water, gradually increasing the ratio with each serving. At what point has the "original" wine become "untouched" ? You'd probably say "at the moment that I began detecting the dilution", which is precisely the point I am trying to highlight ! Well, the RAW file format is the equivalent of the "original untouched" vintage claret and the Jpeg is the slightly watered down version of it. There are numerous factors which enter into this equation, not least the algorithm which is chosen by software engineers to interpret the data coming directly off the CCD. IMHO Pentax have given users a remarkably advanced choice of variable options in determining how Jpeg's exit the K10D (by comparison with competing manufacturers), so if you select the RAW + Jpeg setting, you surely have the best of both world's ???

Last edited by Confused; 07-21-2007 at 05:07 PM.
07-21-2007, 07:11 PM   #19
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Confused - c. r. brown mentioned OGG Vorbis, Ape, FLAC and Apple Lossless formats, which are LOSSLESS :-), just like DNGs, and compressed PEFs (and WinZip). I don't think anyone here is claiming that mp3 is a lossless format.

I have worked with APE files before (I'm a musician/audio engineer in one of my many other lives) and they are definetly lossless. I've compressed a WAV file, and then uncompressed it and then did a bit-compare, and nothing was lost in the CODEC process.

WinZip is another lossless CODEC. JPG/mp3 is LOSSY. Big difference!

07-21-2007, 08:01 PM   #20
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QuoteOriginally posted by hamsi Quote
Entropy, c.r.brown, thank you for your quick responses.
when I unzip the compressed files by "winzip" or "winrar" they are same size again, not smaller. So I expect to get same size DNGs after converting from PEF. (I think "the size of in camera DNGs" should be equal to "the size of DNGs converted from PEF" since they are both the same format). That's why I'm surprised...
I assume that PEF is a lossless compression; while DNGs converted from PEF and in camera DNGs are both uncompressed.
I think if PEF were a lossless compression, DNG's converted from PEF wouldn't be smaller than in-camera DNG's. Where am I wrong?

I wonder if there is a test can prove that "PEF" and "DNGs converted from PEF" are both lossless as "in-camera DNGs"?
...seeing is believing...
Not all compression algorithms are created equally. Algorithms like ZIP, RAR, 7zip, bzip2, and RAR are intended to be "generic" algorithms that try to perform as best as they can in all situations. Even within these "generic" algorithms there is variation in performance. 7zip blows away gzip and the original LZH-based ZIP algorithm in almost all situations, and is somewhat better than bzip2 (which also beats all of the others in nearly all situations), but takes far more CPU time and memory to compress and decompress.

Given specific types of input data (such as audio or an image) it is possible to develop special algorithms that maximize efficiency for that type of input data while sacrificing efficiency on other types. For example, image data is two dimensional, so given knowledge of that it is possible to optimize the compression scheme given that knowledge compared to a "one dimensional" algorithm like ZIP, gzip, or bzip2.

For example, I believe the JPEG algorithm consists primarily of three parts:
Discrete Cosine Transform (converts space/time-domain information into frequency-domain information - lossless) - This is basically a step that converts the data into something "easier" to compress
Quantization of the frequency domain information (lossy)
Huffman encoding of the resulting information (lossless)

There is support for lossless JPEG compression, although most encoders (and many decoders) don't implement it. It basically uses the two lossless steps from above.
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