RAW to sRAW from DSLR

awdark

RAW to sRAW from DSLR

« on: 26 / December / 2010, 13:20:00 »

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Hi,
I know we usually talk about the RAW files we pull from CHDK but I was wondering if its possible to convert a Canon CR2 to sRAW where we discard a few megapixels worth of data but get a more manageable sized file.

I know it would need to discard some data, will probably need to do some interpolation, and some logic (since you would want to discard the "noisy" pixels anyways)

But does a program like that exist? I asked on another forum and they said the best I can do is convert the CR2 to DNG with better compression but well

you guys might know something.

I would appreciate any input and ideas because my camera takes 18mp shots where RAW+JPG = ~30mb and that adds up!

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vit40

Re: RAW to sRAW from DSLR

« Reply #1 on: 27 / December / 2010, 03:38:02 »

I think there's no such a program provided by Canon or someone else

BTW, sRAW is quite different from other RAW formats. It's not RGB data from sensor, but already demosaicked raw file, resized to smaller size and converted to sort of Y Cr Cb format

BTW2, you won't get better compression with dng, because both cr2 and dng are using lossless jpeg compression. However, RAW+JPG is actually (RAW+JPG)+JPG, because you have raw image and jpeg image in a cr2 file + jpg image in separate file (at least in older Canon cameras, like my 400D). Compressing to dng, you get rid of jpg that was embedded in cr2, so dng IS smaller than cr2, because it contains only a raw image (+ some metadata and small jpg thumbnail)

« Last Edit: 27 / December / 2010, 03:41:24 by vit40 »

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awdark

Re: RAW to sRAW from DSLR

« Reply #2 on: 27 / December / 2010, 12:48:17 »

Wouldn't the CR2 format be similar to the sRAW format then? I'm pretty sure it has more processed information than what we have in our truly raw files from CHDK.

I didn't know that about the CR2 containing the JPG also.. I will need to read into it and see if I can have a program that can quickly access the CR2 files and just skip the 6mb jpg.

new dslr = $ regret and now storage regrets haha.

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vit40

Re: RAW to sRAW from DSLR

« Reply #3 on: 27 / December / 2010, 14:48:35 »

You can extract jpeg embedded inside cr2 with freware program dcraw (command line utility), so you can see how big it is for your camera. Syntax is

dcraw -e <filename>

In case of 400D, I have an option to save "raw" or "raw+L"
"raw" has half-size jpeg inside cr2, which has usually about 600 kB
"raw+jpg" has full size jpeg inside cr2, which is usually more than 2 MB, so cr2 in "raw+jpg" mode is bigger than in "raw" mode

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awdark

Re: RAW to sRAW from DSLR

« Reply #4 on: 28 / December / 2010, 00:19:50 »

For me its
26mb for cr2 + 7.18mb jpg

I extracted the JPG from the cr2 and it was 2.75mb. However it is the same resolution and apparently has a lot more compression.

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vit40

Re: RAW to sRAW from DSLR

« Reply #5 on: 28 / December / 2010, 04:50:17 »

In my case "raw" option produces about 10 MB cr2. It is 10 Mpix and 12 bit
In your case, it has, besides 18 Mpix, probably also 14 bit, so it's considerably bigger

Converting cr2 to dng should reduce the size by approximately the size of embedded jpeg

You can also find some info about sRaw here (quite technical stuff)

http://dougkerr.net/Pumpkin/articles/sRaw.pdf

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awdark

Re: RAW to sRAW from DSLR

« Reply #6 on: 29 / December / 2010, 23:27:23 »

Thanks for sharing that. Was a good read when I had free time at work. You were serious when you said technical, reminded me of CS451 Multimedia Software Systems... didn't do good in that class <_<;

I guess there isn't much of a demand to drop the resolution of the raw to save space. But thank you for all the info.

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