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RAW Files Size on S5 IS

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Offline davitof

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RAW Files Size on S5 IS
« on: 06 / December / 2008, 07:29:23 »
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I have been wondering about numbers for a few days: I don't know how many bits / pixel are stored in a S5 CRW but let's say there are 8 (I hope for at least 10, of course). I don't know if CRW has 2 green measurements for each pixel, but let's say it has only 1. 8 000 000 pixels * 8 bits * 3 colors = 192 000 000 bits, 24 000 000 bytes.

My problem: CHDK CRWs for the S5 IS are 10 341 600 bytes, less than half of what I expected.

Just to be sure, let's do the calculations the other way: 10 341 600 bytes * 8 bits / 8 000 000 pixels = 10.34 bits per pixel, not even 4 bits per color!

Of course, I thought of compression, but
- I found several references here saying that CHDK RAWs were not compressed
- all CHDK CRWs are the same size, which seems strange for compressed files.

Does anyone have an explanation for this paradox?
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Frederic Da Vitoria
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Offline fe50

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Re: RAW Files Size on S5 IS
« Reply #1 on: 06 / December / 2008, 07:42:23 »
Hello & welcome davitof !

Most Canon P&S cameras has 10 Bit raws.

You'll find some informations about the RAW sensor data here: Bit depth of raw files?
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Offline davitof

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Re: RAW Files Size on S5 IS
« Reply #2 on: 06 / December / 2008, 08:06:00 »
Thanks. And sorry, I forgot to say "hello" in my first post.

I had guessed there were 10 bits per pixel, just as I guess there are actually 2 green samples per pixel (at least UFRaw behaves as there are 2 green, he multiplies red and blue by 2). But this makes my problem only more difficult to understand...

... or was I completely mistaken? each pixel in a RAW is either red or green or blue? Which would mean that in a way, the S5 IS is actually a 2 MPx digicam  :o
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Frederic Da Vitoria
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Offline davitof

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Re: RAW Files Size on S5 IS
« Reply #3 on: 06 / December / 2008, 08:21:16 »
Ok, that's it. Sad but true...

I have been using digicams for 6 years and I always believed that a sensor pixel measured all 3 colors. What a disappointment!
« Last Edit: 06 / December / 2008, 08:24:34 by davitof »
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Frederic Da Vitoria
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