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05-25-2011, 02:34 PM   #1
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Jean Poitiers's Avatar

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DNG file sizes with a K-7


OK, this is probably going to be a stupid "rookie" question ...

Was shooting my kids and zoo animals today and noticed at home that the DNG file sizes seemed quite large ... very first shot in DNG lists as 21.1 Mo and later shots list out at 17.0 Mo, 16.9 Mo, 15.6 Mo, etc. Is this normal ... since the K-7 sensor is only 14.6 Megapixels or am I missing something? Noticed this first while using Picasa, and the Windows application said the same thing as well as the SilkyPix 4 application, too.

Thanks in advance and please excuse me if my ignorance is showing ... J

05-25-2011, 02:38 PM   #2
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That sounds possible. I shoot PEF which is generally a bit smaller file size and was in the 12-15mb range, sometimes around 18mb. Using better lenses can push the file size up, as will a "busy" subject.
05-25-2011, 03:33 PM   #3
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Thats right, the size of the file is not directly coresponding to the size of the sensor, rather the amount of info stored in the file itself. A 14.6 mgpixl sensor does not mean the files will be 14.6 meg, the sensor measurement is resolution, the file size is the information needed to map the image created. I find the darker the photo, the bigger the file. My old istD* would give me 17meg files from a 6mgpixl sensor, the K-7 often delivers 15-18meg files, depending on the shot. I think we all wondered about this when first diving into digital side.

Last edited by cmohr; 05-25-2011 at 03:44 PM.
05-25-2011, 04:08 PM   #4
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Megapixel is not the same as megabyte. Each pixel in a RAW file would be represented as at least two bytes, plus there is other information that is recorded in the file as well. So you'd expect an uncompressed RAW file to be somewhat more than twice as many (mega)bytes as the camera has (mega)pixels. The fact that the file is actually smaller than this is because the K-7 compresses the data (as do all Pentax cameras made the last few years as far as I know).

05-26-2011, 01:10 PM   #5
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"Bonjour" Marc, SpecialK and cmohr,

"Merci" for your help and I just love this forum. Great help, support and general info. Really appreciated since I'm now living far away from Paris where I could get info a lot easier than here in Poitiers. Only one real camera store and no photo clubs here to speak of ...

A lot of the RAW files were coming in "large" at above 15Mo and I knew that there was some compression, etc. It's just that the big file(s) worried me since I bought my K-7 used (6600 clicks) about a month and a half ago. Steep learning curve here for me. Have a K110D and then bought a K-r which my wife immediately claimed for herself ... then came across the used K-7, had some reservations, but went for it.

Thanks again and I'll probably have more "novice" type questions in the future ... "à bientôt", John

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