Black corners in RAW (CRW and DNG formats) - RAW Shooting and Processing - CHDK Forum
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Black corners in RAW (CRW and DNG formats)

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Offline CharlieMAC

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Black corners in RAW (CRW and DNG formats)
« on: 27 / December / 2014, 10:51:50 »
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Hi folks!

I'm learning how to post processing the raw images using UFRAW (Linux tool), but all the photos have black corners. I haven't been able to remove them using this program (I don't know any other tool so far), so, does it have to do with the CHDK version or camera specific or the UFRAW itself?

There are the comparison between the JPEG output vs the RAW output below. Here are my settings:

Cam: SX150 IS
CHDK Ver.: 1.3.0 - rev 3874 - Dec 8 2014
FW ver.: 100a
Compiler: GCC 4.4.3

Any ideas?
Best,

C.
« Last Edit: 27 / December / 2014, 10:54:20 by CharlieMAC »
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Offline ursamajor

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Re: Black corners in RAW (CRW and DNG formats)
« Reply #1 on: 27 / December / 2014, 11:55:40 »
You must use a software or a plugin for correction of barrel aberration. Or simply, but not with good results, crop the corners. The phenomenon appears because of barrel distorsion and consist in vignetting the corners. On the other hand, Jpegs are corrected by Canon in-camera software.

I recommend you RAW Therapee (free) who can correct both barrel and pincushion distortions.
In ufraw you have also Lens correction option, but you must crop manually the photos.
« Last Edit: 27 / December / 2014, 12:35:12 by ursamajor »
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Online reyalp

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Re: Black corners in RAW (CRW and DNG formats)
« Reply #2 on: 27 / December / 2014, 15:14:19 »
You can correct some vignetting with flat field images, though obviously not the parts where it is completely dark. RAW Therapee has some flat field support.

As ursamajor says, the dark corners are there in the raw data, it's not a bug in CHDK or ufraw. If you look carefully, you'll see the raw contains a significantly wider field of view than the camera jpeg. The Canon firmware un-distorts and crops when it make the jpeg.
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Offline blackhole

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Re: Black corners in RAW (CRW and DNG formats)
« Reply #3 on: 27 / December / 2014, 16:50:48 »
Cropping is there only solution.Cone of light at wide angle does not cover the entire surface of the sensor.
What is happen if you in RAW/DNG menu ,specify JPEG as DNG Crop size?
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Offline fabri22

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Re: Black corners in RAW (CRW and DNG formats)
« Reply #4 on: 27 / December / 2014, 17:48:45 »
It would be interesting to know if all 4 corners are black or only the upper ones, as it seems in your raw sample.
If only 2 are black then your lens could be misaligned ... or raw size and pos. statements in SX150 CHDK porting could be wrong.

my 2 cents...
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Offline CharlieMAC

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Re: Black corners in RAW (CRW and DNG formats)
« Reply #5 on: 27 / December / 2014, 19:35:18 »
Quote from: blackhole on 27 / December / 2014, 16:50:48
Cropping is there only solution.Cone of light at wide angle does not cover the entire surface of the sensor.
What is happen if you in RAW/DNG menu ,specify JPEG as DNG Crop size?

That is the current option.


Quote from: fabri22 on 27 / December / 2014, 17:48:45
It would be interesting to know if all 4 corners are black or only the upper ones, as it seems in your raw sample.
If only 2 are black then your lens could be misaligned ... or raw size and pos. statements in SX150 CHDK porting could be wrong.

my 2 cents...

Well, I'm not completely sure because one of the corners seems to be a little darkened, but not totally blacked. For sure, 3 out of 4 corners are black and 2 of them are bigger than the third, as you can appreciate in the RAW picture below.

So, if the lens is misaligned (i dropped the camera accidentaly once... :( ), how could I realign it?

Thanks for your quick replies!
Best,

C.
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Offline fabri22

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Re: Black corners in RAW (CRW and DNG formats)
« Reply #6 on: 27 / December / 2014, 20:15:57 »
See if black corners are minimized shooting while gently pushing the lens barrel in the red arrow direction.
« Last Edit: 27 / December / 2014, 20:25:30 by fabri22 »
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Offline philmoz

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Re: Black corners in RAW (CRW and DNG formats)
« Reply #7 on: 27 / December / 2014, 20:31:21 »
Quote from: CharlieMAC on 27 / December / 2014, 19:35:18
Quote from: blackhole on 27 / December / 2014, 16:50:48
Cropping is there only solution.Cone of light at wide angle does not cover the entire surface of the sensor.
What is happen if you in RAW/DNG menu ,specify JPEG as DNG Crop size?

That is the current option.


Quote from: fabri22 on 27 / December / 2014, 17:48:45
It would be interesting to know if all 4 corners are black or only the upper ones, as it seems in your raw sample.
If only 2 are black then your lens could be misaligned ... or raw size and pos. statements in SX150 CHDK porting could be wrong.

my 2 cents...

Well, I'm not completely sure because one of the corners seems to be a little darkened, but not totally blacked. For sure, 3 out of 4 corners are black and 2 of them are bigger than the third, as you can appreciate in the RAW picture below.

So, if the lens is misaligned (i dropped the camera accidentaly once... :( ), how could I realign it?

Thanks for your quick replies!
Best,

C.

Thats normal for current Canon cameras - as already mentioned the camera does distortion correction on the JPEG image to remove this. The CHDK RAW/DNG has no correction applied so you have to do it yourself in post-processing.

Don't go pushing on the lens or trying to adjust it - you will only break the camera. A misaligned lens will cause softness on one side, not this effect.

If you set the DNG crop size to 'Full' and upload a DNG from the camera to a file sharing site, we can check the DNG active area to make sure it is set correctly. This will only fix minor alignment issues though.

Phil.
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Offline fabri22

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Re: Black corners in RAW (CRW and DNG formats)
« Reply #8 on: 27 / December / 2014, 20:34:51 »
Ubi maior minor cessat ...  :)
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Offline ursamajor

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Re: Black corners in RAW (CRW and DNG formats)
« Reply #9 on: 28 / December / 2014, 02:44:44 »
Quote from: CharlieMAC on 27 / December / 2014, 19:35:18
So, if the lens is misaligned (i dropped the camera accidentaly once... :( ), how could I realign it?

Thanks for your quick replies!
Best,

C.

No, it's not misaligned. My SX150IS take identical pictures, with only upper corners black and just a little down left. Let the lens in peace!
If the lens were misaligned, you would have out of focus zones.
« Last Edit: 28 / December / 2014, 02:49:10 by ursamajor »
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