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DNG wrong values with costum auto iso

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DNG wrong values with costum auto iso
« on: 01 / September / 2012, 06:59:20 »
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Hi there,

I am using CHDK 1.2.0.2104 with my S100 and it is a great software. Recently I discovered a strange thing. I was checking out the DNG-feature and got the following results:

1.) Somewhere in the manual there is told, you can only create dng-files when setting the cam to jpg, when setting to raw the dng won´t work. That´s wrong, when I set the cam to create raw (canon-raw-cr2) there is created a dng-file also. For my opinion that´s cool because it´s the best way to compare if there´s a quality difference between canon-cr2-raw and chdk-dng.

2.) That´s the main reason for my posting. In the custom auto iso I set the maximum shutter speed to 1/30, a minimum iso of 100 and chose a aperture of 3,2. This was the result, remember both files were created at once!

Canon raw cr2: Picture1-> Iso 100, aperture 3,2, shutter speed 1/30 ; Picture 2-> Iso 100, aperture 3,2, shutter speed  1/320
CHDK dng: Picture1-> Iso 50, aperture 3,3, shutter speed  1/30 ; Picture 2-> Iso 50, aperture 3,3, shutter speed  1/350

How can that be? Why does chdk don´t abide by the custom auto iso when creating dngs?
« Last Edit: 01 / September / 2012, 07:04:32 by stw500 »

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Offline reyalp

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Re: DNG wrong values with costum auto iso
« Reply #1 on: 01 / September / 2012, 15:57:49 »
CHDK and Canon exif values may not be reporting the same thing, (you can also see the shutter and aperture are slightly different). For ISO, Canon uses two different values "real" and "market" as discussed here: http://chdk.wikia.com/wiki/CHDK_User_Manual#Override_ISO_value

That doesn't completely solve the puzzle though, because in general CHDK should work entirely in "real" values, so a minimum of 100 should result in 100 in the CHDK case ("real") and something a bit higher in the Canon case ("market")

Quote
1.) Somewhere in the manual there is told, you can only create dng-files when setting the cam to jpg, when setting to raw the dng won´t work.
CHDK doesn't know or care about Canon RAW at all. The confusion may be that CHDK also supports "CHDK raw" which is just a sensor dump but is usually saved with a CR2 or CRW extension. You cannot save this at the same time as DNG.
Don't forget what the H stands for.

Re: DNG wrong values with costum auto iso
« Reply #2 on: 03 / September / 2012, 02:26:14 »
Quote
1.) Somewhere in the manual there is told, you can only create dng-files when setting the cam to jpg, when setting to raw the dng won´t work.
CHDK doesn't know or care about Canon RAW at all. The confusion may be that CHDK also supports "CHDK raw" which is just a sensor dump but is usually saved with a CR2 or CRW extension. You cannot save this at the same time as DNG.

Not really. In the german chdk-manual on page 26 there is said, activation shooting in raw in the canon-menu will disable chdk-raw (and this way also creating dng-files). In the english manual I could´t find this hint, but i didn´t read it to the end.

Re: DNG wrong values with costum auto iso
« Reply #3 on: 03 / September / 2012, 02:27:54 »
CHDK and Canon exif values may not be reporting the same thing, (you can also see the shutter and aperture are slightly different). For ISO, Canon uses two different values "real" and "market" as discussed here: http://chdk.wikia.com/wiki/CHDK_User_Manual#Override_ISO_value

That doesn't completely solve the puzzle though, because in general CHDK should work entirely in "real" values, so a minimum of 100 should result in 100 in the CHDK case ("real") and something a bit higher in the Canon case ("market")

This is true and I don´t understand it at all. At least it is not only a reporting thing, because the dng-files are darker (lower iso) than the canon-raws.
« Last Edit: 03 / September / 2012, 02:29:33 by stw500 »


Re: DNG wrong values with costum auto iso
« Reply #4 on: 03 / September / 2012, 11:06:50 »
At least it is not only a reporting thing, because the dng-files are darker (lower iso) than the canon-raws.
Do we know what kind of corrections Canon applies to images before saving them as RAW ?  Lens distortion ?  Color balance ? Luminance ?

I've always assumed they do more than the raw sensor dump you get with CHDK.  They just skip the compression step necessary to produce a JPG ?

Update :  my G10 does Canon RAW - I guess I could try some test shots although I'm not sure anything reads CHDK G10 RAW and the DNG option adds the color_matrix to the test ....
« Last Edit: 03 / September / 2012, 11:08:25 by waterwingz »
Ported :   A1200    SD940   G10    Powershot N    G16

Re: DNG wrong values with costum auto iso
« Reply #5 on: 26 / November / 2012, 00:14:40 »
I'm finding that my CHDK 1.1 DNG's give wrong exposure time, they are limited to 15s where they are really 240s or more.  Maybe it has to do with DNG 1.1 or 1.3.  I heard the option is there for compatibililty with difference software.
Also 1.3 includes the bad pixel list.

Also my DNG's don't decode in special ISO3200 mode.  I believe in this mode, the camera uses super pixels, meaning the 4 bayer pixels are taken as one pixel, for less noise and less resolution.

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Offline reyalp

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Re: DNG wrong values with costum auto iso
« Reply #6 on: 26 / November / 2012, 01:39:49 »
I'm finding that my CHDK 1.1 DNG's give wrong exposure time, they are limited to 15s where they are really 240s or more.  Maybe it has to do with DNG 1.1 or 1.3.
No, it wouldn't have anything to do with DNG version. Which camera do you have?
Quote
Also my DNG's don't decode in special ISO3200 mode.
A valid raw buffer likely does not exist in this mode, so the DNG data will just be random garbage from memory. CHDK should disable raw/DNG in modes like this, but doesn't do it correctly for every camera.
Don't forget what the H stands for.

 

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