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04-01-2010, 08:44 PM   #1
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K7 RAW file size

Hi:

I have been shooting with the K7 and noticed when I shoot in RAW, which is almost always, the file sizes are significantly smaller then K20d RAW files. The K20d's RAW file sizes are about 22-23 mb, but the K7's are between 11- 13 mb.

Am I missing something or perhaps used an incorrect camera setting? I just want to make sure I am not giving away important data that could be useful in post processing, since CS4 often saves me as I work on my lighting technique!!

Thanx so much.

Gregg

04-01-2010, 09:54 PM   #2
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The K7 is compressing the raw files, the K20 isn't.
Enjoy your new found hard drive space.
04-01-2010, 10:16 PM   #3
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Hi:

Thanx so much Wheatfield. At the risk of sounding like a dunderhead, is that compression lossless or does it have an affect upon image quality? I usually think of compression being bad for image quality. Is that not the case here?

Thanx again.

Gregg
04-02-2010, 08:56 AM   #4
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It is lossless, which to me is some sort of voodoo.
Since the file is only compressed once, even if it was lossy, it wouldn't be a big deal.
For example, jpeg is known to be lossy compression, but if you shoot a jepg and then after processing it you save it as a tiff or some other lossless compression (I use psd), you are unlikely to see any image degradation in the final print, though pixel peepers may see some artifacting and will usually have kittens about it.
It's only when you make small alterations to a file and then resave it multiple times in a lossy format that things can go sideways.

04-02-2010, 09:46 AM   #5
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BTW, are you talking about DNG or PEF? I thought the K20D compressed PEF but not DNG - that's the case with my K200D, which was released around the same time. But I do recall hearing K7 compressed both. If you're seeing a size difference with DNG, that explains it, but I'd be surprised to see it with PEF.

BTW, as for lossless compression bieng "voodoo" - it's actually the lossy compressions in JPEG that are *really* complex and scary. Lossless compression is a relatively simple concept in comparison, at least in it's simplest form. For example:

"0000000000000000000000000000000000000000000000000000000000001"

versus

"60 0's followed by a 1"

Which takes more space? That's the essence of how the most basic form of lossless compression works: look for strings of similar info and reduce it like I did above. There are far more clever ways of going about it, and those can get amazingly complex, but they are pretty well understood in the software world because they can apply to any sort of data. But as long as your goal is to exactly reproduce a given binary sequence, it's easy enough to check whether your algorithm makes sense. It's figuring out how much information you can afford to lose without causing obvious problems - and which bits are more important than which - that goes way beyond what even someone with a degree in computer science would typically be able to deal with, unless he happened to have specialized in graphics algorithms.
04-03-2010, 06:19 PM   #6
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Thanx so much for your replies. So long as the compression is lossless I welcome the additional space. It just took me by surprise.

Gregg
04-07-2010, 08:29 AM   #7
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I just checked my K7 RAW files/PEF format. They range from 18mg-24mg.
04-07-2010, 08:32 AM   #8
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I also just checked (1) K20 file, again PEF and it was 14mg.

04-07-2010, 05:43 PM   #9
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Basically, lossless compression uses similar algorithms to those used for basic file archiving and compression, similar (or identical) to formats that you're probably familiar with such as zip, lzw, etc.

None of these archival compression formats lose data - they just (as stated eloquently by Marc), simplify the expression of that data by representing it differently in the storage format; consider the difference between a number represented as decimal, vs one represented as binary vs one represented as hexidecimal:

2754 (decimal) vs. 101011000010 (binary) vs AC2 (hexidecimal)

...which are equivalent.

This isn't precisely how it works, but the bottom line is that equivalent values can be stored in different notations, and some notations are less 'space-consuming' than others (ie. require less characters).

The tradeoff—as you've experienced with zipping/unzipping files—is that you need to spend extra computational cycles, and consequently more time, converting between notations when you want to work with the data vs. storing the data.
04-07-2010, 09:43 PM   #10
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I really wish that more cameras would compress the RAW space. Amazing how a 10 megapixel camera can have up to 30mb files. You know what that does to a hard drive?
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