A720: CRW files too small (~10 MB) with only 2 Megapixels

Derandi

3

« on: 28 / March / 2009, 07:13:29 »

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This is the version of CHDK I just managed to install:

a720-100c-0.9.7-725-full

After doing some tests with actived RAW I noticed that the RAW pictures are only a quarter of the size of the JPEG pictures

. They have about 2 megapixels, compared to 8 megapixels in the jpeg files. I do not think it's a probem of "Raw Photo Processor", because every single RAW file is only 9,99 MB, and one cannot save 30 bits per pixel and eight megapixels within 10 megabytes (must be about 24 megabytes).

Does this make any sense? I looked the FAQ and Google up and down and found: NOTHING?!? Am I stupid?

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whim

2046
A495/590/620/630 ixus70/115/220/230/300/870 S95

Re: A720: CRW files too small (~10 MB) with only 2 Megapixels

« Reply #1 on: 28 / March / 2009, 07:24:03 »

According to this page: http://chdk.wikia.com/wiki/CameraFeatures

your cam should produce RAWs of 10,341,600 bytes / Resolution 3298 x 2472 (JPG 3264 x 2448)

so it seems everything is as it should be ...

wim

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fe50

3147
IXUS50 & 860, SX10 Star WARs-Star RAWs

Re: A720: CRW files too small (~10 MB) with only 2 Megapixels

« Reply #2 on: 28 / March / 2009, 07:31:06 »

Quote from: Derandi on 28 / March / 2009, 07:13:29

They have about 2 megapixels, compared to 8 megapixels in the jpeg files. I do not think it's a probem of "Raw Photo Processor",

Many viewers / image processing tools shows either 1/2 the image or only a small thumbnail of RAW files by default due to performance/faster response...e.g. in XNView: "Camera RAW: jalf size / full size / thumbnail only"

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Derandi

3

Re: A720: CRW files too small (~10 MB) with only 2 Megapixels

« Reply #3 on: 29 / March / 2009, 19:41:26 »

Thank you. Yes, you are right, the table shows the correct file size, and instead of using RPP I tried to import the CRW file to GraphicConverter. Indeed, GraphicConverter shows the full picture size of 3298x2472. When taking a closer look to RPP I noticed a nearly hidden option "Interp". that allows to choose among VCDMF, AHDMF and Half. The latter was default and caused the image resolution reduction which I noticed.

What's still unclear: How is it possible to store 8 million x 3 x 10 bits to a 10 megabytes file without compressing? Or are neighbour pixels not completely independent, and there is a kind of delta coding?

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reyalp

14082

Re: A720: CRW files too small (~10 MB) with only 2 Megapixels

« Reply #4 on: 29 / March / 2009, 21:19:05 »

You are assuming the megapixel count refers to RGB triplets. It doesn't. See bayer filter. When the camera (and most raw software) processes this into an RGB image, it interpolates to make an RGB with the same number of pixels.

You might view this as dishonest marketing, but the luminance information does have the given resolution.

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