Compresses RAW on the A700

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johnb74
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Compresses RAW on the A700

Unread postby johnb74 » Sat Nov 24, 2007 6:15 pm

Does anyone know for certain whether the compressed RAW format in the A700 uses lossy or lossless compression? The manual says nothing on this point.
If it uses lossless compression, nothing is lost by selecting cRAW, so why is RAW provided as well. or am I missing the point?

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Omega892
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Re: Compresses RAW on the A700

Unread postby Omega892 » Sat Nov 24, 2007 6:34 pm

johnb74 wrote:Does anyone know for certain whether the compressed RAW format in the A700 uses lossy or lossless compression? The manual says nothing on this point.
If it uses lossless compression, nothing is lost by selecting cRAW, so why is RAW provided as well. or am I missing the point?

Maybe its a bit like the TIFF format which can save as compressed, losseless, or not.

Maybe what is gained by RAW is a little extra speed in storing the image on the card with cRAW a little slower but increasing the number of shots that any card will hold.

OTOH I could be talking complete true. :)
'Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.' - Benjamin Franklin

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Dr. Harout
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Unread postby Dr. Harout » Sat Nov 24, 2007 7:26 pm

Allow me to true too.
Whenever and whatever you compress (in other words: squeeze) something (or anything) will burst or ooze or drop out of it. :twisted:
But don't worry, if you're not thinking of professional quality printing (biggest and largest sizes), then opt for cRaw.
One way or another it's much better than jpeg quality! 8)

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Unread postby rogprov » Sun Nov 25, 2007 7:20 am

Sony says clearly and unequivocally:

Question: Are there any differences in picture quality between cRAW and RAW?

Sony Answer : No, there is no differences. Quality is not a problem even when compressed, but for those users who like uncompressed data, we left the uncompressed raw data support.

So there you have it, in other words "We knew there'd be whining if we only gave you cRAW so we left the RAW as well so you could test both out until you were convinced" :)

Roger

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Unread postby David Kilpatrick » Tue Nov 27, 2007 2:20 am

Sony's image-data order allows easy run-length compression - lossless. It is a bit of a mystery why they include uncompressed RAW, except maybe to future-proof the files by allowing trial and error interpretation.

David

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Re: Compresses RAW on the A700

Unread postby bossel » Mon Jul 21, 2008 4:27 pm

I remember some pretty heated discussions on cRaw on dyxum, do a search there.

One guy reprogrammed what was required to decode it and compared to RAW.

IIRC, the outcome was that it is lossless with the exception of high contrast edges, where a minimal loss could occur.

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Re: Compresses RAW on the A700

Unread postby Hawk » Mon Jul 21, 2008 7:15 pm

Maybe its a bit off topic but week or so ago I accidentaly deleted one RAW photo. Since I already deleted it from card too at first I was sure it was lost forever. But wait, when you delete photo from card it isn't really deleted, just information in file allocation table is changed. Since I wasn't shooting too much after clearing memory card there was still possibility that my photo wasn't overwritten yet.

I didn't wanted to buy some recovery program to restore single image so I used free PhotoRec. Yes, it found my file and it was identified as TIFF. Data converter correctly identified is as RAW and it opened correctly. I wasn't investigating it further, but it seems that ARW format may be simply TIFF image + some additional data stored by camera. If its true then most likely cRAW format may be simple compressed TIFF + additional camera data. However TIFF may use JPEG compression :(

Anyway, just wanted to share this info.

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Re: Compresses RAW on the A700

Unread postby David Kilpatrick » Mon Jul 21, 2008 8:30 pm

All raw files are actually TIFFs - or more accurately, RIFFs or TRIFFs - Raster Image File Format or Tagged Raster Image File Format. You can open them directly, and view the raw Bayer pattern data, if you know the dimensions and the byte order and have a program which ignored the header resources and identifies the image data only. TIFF or TIF is just a shortening of a tagged raster image file.

David


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