How to interpolate or remove black pixels in DNG files - RAW Shooting and Processing - CHDK Forum
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How to interpolate or remove black pixels in DNG files

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Offline hari-bhari

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How to interpolate or remove black pixels in DNG files
« on: 19 / March / 2012, 12:26:50 »
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I am using an SD4000 with CHDK to shoot in DNG format. I ran the built-in badpixel script to generate the badpixel.bin file and the camera is able to shoot and create DNG files. However, when loading the files into Photoshop RAW editor, there are several hundred (or more) black pixels throughout the image. I have tried with the badpixel removal options set to off, average, and rawConv with no difference between the images. I have also tried all the options for dark frame subtraction with the same results. I am assuming that these black pixels in my images are the stuck or bad pixels on the sensor. My question is, how do I get rid of these?? I can't find any options for noise reduction or interpolation in the raw editor. Any help is appreciated!
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Offline philmoz

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Re: How to interpolate or remove black pixels in DNG files
« Reply #1 on: 19 / March / 2012, 14:58:47 »
Quote from: hari-bhari on 19 / March / 2012, 12:26:50
I am using an SD4000 with CHDK to shoot in DNG format. I ran the built-in badpixel script to generate the badpixel.bin file and the camera is able to shoot and create DNG files. However, when loading the files into Photoshop RAW editor, there are several hundred (or more) black pixels throughout the image. I have tried with the badpixel removal options set to off, average, and rawConv with no difference between the images. I have also tried all the options for dark frame subtraction with the same results. I am assuming that these black pixels in my images are the stuck or bad pixels on the sensor. My question is, how do I get rid of these?? I can't find any options for noise reduction or interpolation in the raw editor. Any help is appreciated!

Try re-running the badpixel.bin create function at a high ISO.

Phil.
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Offline hari-bhari

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Re: How to interpolate or remove black pixels in DNG files
« Reply #2 on: 20 / March / 2012, 23:04:09 »
wow this actually seems to work, the black pixels are gone! my bad pixel count was 60k though, compared to about 20k before. what is the reasoning behind performing this step at high ISO? also does it matter what subject i shoot? i seem to get better results shooting a lighted subject than in a dark room (as the wiki seemed to suggest). one thing i noticed is that the dng files have a lot of noise compared to the jpg shots (i am assuming they have been noise reduced). does the badpixel count affect this? thanks!

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Offline philmoz

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Re: How to interpolate or remove black pixels in DNG files
« Reply #3 on: 21 / March / 2012, 00:00:27 »
Quote from: hari-bhari on 20 / March / 2012, 23:04:09
wow this actually seems to work, the black pixels are gone! my bad pixel count was 60k though, compared to about 20k before. what is the reasoning behind performing this step at high ISO?

This seems to be a feature with the new CMOS sensors.

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also does it matter what subject i shoot? i seem to get better results shooting a lighted subject than in a dark room (as the wiki seemed to suggest).

Not as far as I know.

Quote
one thing i noticed is that the dng files have a lot of noise compared to the jpg shots (i am assuming they have been noise reduced). does the badpixel count affect this? thanks!

The camera is doing noise reduction before converting to JPEG; but CHDK saves the DNG before this so you are getting the actual sensor data. Noise and bad pixels are two different things.

Phil.
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  g12 (1.00c, 1.00e, 1.00f & 1.00g)
  sx130is (1.01d & 1.01f)
  ixus310hs (1.00a & 1.01a)
  sx40hs (1.00d, 1.00g & 1.00i)
  g1x (1.00e, 1.00f & 1.00g)
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Offline hari-bhari

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Re: How to interpolate or remove black pixels in DNG files
« Reply #4 on: 23 / March / 2012, 15:03:26 »
ok so ive done the badpixel creation at ISO 1600 and it's found around 90k or so badpixels. the black dots in my images are gone but they are replaced with multicolored pixels in my pictures (different from just noise), always in the same spots. this happens at any ISO over 400. none of the noise reduction algorithms in photoshop raw are able to remove these. I have tried all three settings for dark frame subtraction and all three settings for badpixel removal (which i don't think affects DNG files), with no results. any help??

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Offline philmoz

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Re: How to interpolate or remove black pixels in DNG files
« Reply #5 on: 23 / March / 2012, 16:37:41 »
Quote from: hari-bhari on 23 / March / 2012, 15:03:26
ok so ive done the badpixel creation at ISO 1600 and it's found around 90k or so badpixels. the black dots in my images are gone but they are replaced with multicolored pixels in my pictures (different from just noise), always in the same spots. this happens at any ISO over 400. none of the noise reduction algorithms in photoshop raw are able to remove these. I have tried all three settings for dark frame subtraction and all three settings for badpixel removal (which i don't think affects DNG files), with no results. any help??

Upload a DNG file and your badpixel.bin file to a file share site and post the link here, and I'll take a look at it.

Phil.
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CHDK ports:
  sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
  g12 (1.00c, 1.00e, 1.00f & 1.00g)
  sx130is (1.01d & 1.01f)
  ixus310hs (1.00a & 1.01a)
  sx40hs (1.00d, 1.00g & 1.00i)
  g1x (1.00e, 1.00f & 1.00g)
  g5x (1.00c, 1.01a, 1.01b)
  g7x2 (1.01a, 1.01b, 1.10b)
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Offline hari-bhari

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Re: How to interpolate or remove black pixels in DNG files
« Reply #6 on: 25 / March / 2012, 19:50:15 »
Hi Phil,

Thanks for your help thus far. Here are links to the badpixel.bin file and two DNG files that are displaying the hot pixels. Of note, on images with a faster shutter speed, or when I use the flash, there are no hot pixels. Please let me know if you'd like me to upload a file that does not contain the hot pixels.

Hari


http://www.4shared.com/file/Is-QDOb0/file.html
http://www.4shared.com/file/Iewn0r6j/file.html
http://www.4shared.com/file/0ntvCq8Z/file.html


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Offline PS

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Re: How to interpolate or remove black pixels in DNG files
« Reply #7 on: 26 / March / 2012, 12:58:39 »
Those are bad pixels marked by camera with 0 value.
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Offline philmoz

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Re: How to interpolate or remove black pixels in DNG files
« Reply #8 on: 26 / March / 2012, 14:59:17 »
Quote from: hari-bhari on 25 / March / 2012, 19:50:15
Hi Phil,

Thanks for your help thus far. Here are links to the badpixel.bin file and two DNG files that are displaying the hot pixels. Of note, on images with a faster shutter speed, or when I use the flash, there are no hot pixels. Please let me know if you'd like me to upload a file that does not contain the hot pixels.

Hari


http://www.4shared.com/file/Is-QDOb0/file.html
http://www.4shared.com/file/Iewn0r6j/file.html
http://www.4shared.com/file/0ntvCq8Z/file.html


It won't let me download them without signing up for an account - try box.com instead.

Phil.
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CHDK ports:
  sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
  g12 (1.00c, 1.00e, 1.00f & 1.00g)
  sx130is (1.01d & 1.01f)
  ixus310hs (1.00a & 1.01a)
  sx40hs (1.00d, 1.00g & 1.00i)
  g1x (1.00e, 1.00f & 1.00g)
  g5x (1.00c, 1.01a, 1.01b)
  g7x2 (1.01a, 1.01b, 1.10b)
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Offline hari-bhari

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Re: How to interpolate or remove black pixels in DNG files
« Reply #9 on: 26 / March / 2012, 18:41:41 »
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