Badpixel removal

This page contains informations for the Badpixel (Hot-Pixel) removal function FOR DNG IMAGES in CHDK.

To remove defective Pixels in an image in CHDK there's the Bad pixel removal feature. Once you have generated a list with all the "bad" pixels for your camera, CHDK can remove them automatically. The file with the badpixel data is named badpixel (without an filename extension).

• More informations to this feature can be found here: Firmware Usage: Hot-Pixel Removal.

badpixel <--> badpixel.bin

Q: Why are there 2 different files for bad pixel removal, what's the difference ?

A: The badpixel.bin is only needed for DNG creation - it includes the badpixels from the canon firmware. In the RAW image these badpixels are only masked (value = 0), so dependent from the software you use you'll get black dots in your image. The file can be generated with the badpixel.lua script, included in the 'complete' download package; you can also use a dummy file, containing only some zeros: with this you can enable the DNG support, but the bad pixels will not be removed...(Forum link: [1]).

The file badpixel is for the 'standard', usual bad/hotpixel removal (also in JPEGs) - this function removes hotpixels also when they are not known by the canon firmware.

For the new RAW DNG shooting feature a special badpixel file is required, it is named badpixel.bin

This file contains the badpixel informations already stored in the Canon firmware, read more in the forum: Save RAW files in DNG format instead of RAW.

Software

show_bad_b

show_bad_b by ewavr - with this tool you can generate the bad pixel list on a PC.

Usage:

show_bad_b.exe <CHDK_RAW_FILE_NAME>

The output file badpixel.bin is created in the current folder and the defect pixel count is reported.

• Try several RAW files to obtain stable result (approximate shooting conditions: minimal ISO, exposure time ~1/10s).
• Some cameras have two defect pixel lists, which are switched at exposure time ~1/25s. Use the list with maximum (but stable) defect pixel count, otherwise you can see multiple black points on image in some RAW convertors.
• For DNG RAW shooting place the file here: \CHDK\badpixel.bin

badpixel.lua

In the complete download packages there's the script badpixel.lua (located in the folder \CHDK\SCRIPTS\TEST) to generate the badpixel.bin file on the fly in the camera.

Just run the script: it automatically takes 2 pictures, calculates the badpixel data and then it creates the badpixel.bin file. This procedure takes ~ 20-30 s of time, at the end of the process you can save the file with the SET button.

• The current version of the script can be downloaded also directly from the SVN server: badpixel.lua

Links

• show_bad_b: Generate a list of the bad CCD pixels (DOS/Windows): visit download site (click on 'show_bad_b.zip' on the top of the site)
  • alternative download sites: drop.io, zShare.net