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Help on "Bad Pixel Removal"

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Offline dlw

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Help on "Bad Pixel Removal"
« on: 03 / February / 2009, 16:56:35 »
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I'm trying to find out how "Bad Pixel Removal" works for CHDK RAW on a g9 (not DNG'd yet), and I can't find all the information I need on the wiki or forum.  Maybe I haven't used the right search yet?

If I understand the process, I have to create a bad pixel file first.  To do this, I would:

  1.  Take a dark-frame image (or 2 or 3 -- this is a g9, which may have CHDK RAW problems) at the speed I'd like to have corrected.
  2.  Download "show_bad.zip" from ewavr's website.
  3.  Using Windows, run "show_bad raw_file.CRW X > badpixel"
  4.  Convert "badpixel" from ms-dos to unix format and strip out any data after the first two numbers.
  5.  Move "badpixel" to my SD card in the /CHDK/ folder.

Now the "Bad Pixel Removal" menu entry should do something when I enable it.  OK, but it has two settings:  "Average", and "RAWconv".  What is the difference?  What factors would go into my choice of one or the other?

Thanks for taking the time to read this.
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Offline ewavr

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Re: Help on "Bad Pixel Removal"
« Reply #1 on: 03 / February / 2009, 17:44:22 »
Quote from: dlw on 03 / February / 2009, 16:56:35
  4.  Convert "badpixel" from ms-dos to unix format and strip out any data after the first two numbers.
Not necessary, in my camera it works without this.
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  5.  Move "badpixel" to my SD card in the /CHDK/ folder.
Valid name is also "badpixel.txt". If both files "badpixel.txt" and "badpixel" are present in CHDK folder, both lists are merged.
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Now the "Bad Pixel Removal" menu entry should do something when I enable it.  OK, but it has two settings:  "Average", and "RAWconv".  What is the difference? 
"Average" - CHDK makes bad pixel interpolation.
"RAWconv" - CHDK only marks this pixel as bad for interpolation in RAW converter (internal or external).
This option is ignored in DNG mode (in DNG mode bad pixels are averaged by CHDK always).
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What factors would go into my choice of one or the other?
You can compare bad pixel removal quality in both modes (IMO," RAWConv" mode is preferred, because CHDK interpolation is very unsophisticated).
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Offline fe50

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Re: Help on "Bad Pixel Removal"
« Reply #2 on: 03 / February / 2009, 17:52:14 »
Hi dlw,
see also Badpixel_removal & Hot-Pixel_Removal.

Use the G9 CHDK RAWs, not the 'real' Canon RAWs...maybe there could be problems when the G9 RAWs are not ok, just try it...

With XNView it's very easy to compare the images (hotpixel removal enabled/disabled):
- open both images in tabs, locate a hotpixel (use + / - keys to magnify), select a rectangle with the mouse
- save this selection (Menu Edit - Set selection size - Save selection as custom)
- switch to the other (processed) image, press c for the 'Saved selection" feature
You should see the difference  ;)
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bugmenot

Re: Help on "Bad Pixel Removal"
« Reply #3 on: 03 / February / 2009, 19:02:08 »
Quote from: ewavr on 03 / February / 2009, 17:44:22
Quote from: dlw on 03 / February / 2009, 16:56:35
  4.  Convert "badpixel" from ms-dos to unix format and strip out any data after the first two numbers.
Not necessary, in my camera it works without this.
Quote
  5.  Move "badpixel" to my SD card in the /CHDK/ folder.
Valid name is also "badpixel.txt". If both files "badpixel.txt" and "badpixel" are present in CHDK folder, both lists are merged.
Quote
Now the "Bad Pixel Removal" menu entry should do something when I enable it.  OK, but it has two settings:  "Average", and "RAWconv".  What is the difference? 
"Average" - CHDK makes bad pixel interpolation.
"RAWconv" - CHDK only marks this pixel as bad for interpolation in RAW converter (internal or external).
This option is ignored in DNG mode (in DNG mode bad pixels are averaged by CHDK always).
Quote
What factors would go into my choice of one or the other?
You can compare bad pixel removal quality in both modes (IMO," RAWConv" mode is preferred, because CHDK interpolation is very unsophisticated).

then why can't RAWconv be used in DNG mode too?
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Offline ewavr

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Re: Help on "Bad Pixel Removal"
« Reply #4 on: 03 / February / 2009, 19:19:15 »
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bugmenot

Re: Help on "Bad Pixel Removal"
« Reply #5 on: 04 / February / 2009, 02:52:09 »
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Offline dlw

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Re: Help on "Bad Pixel Removal"
« Reply #6 on: 04 / February / 2009, 10:49:26 »
Thank you all very much for clearing this up.  Now I have to fire up a windows pc and start playing with this.
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