4.5 Shooting RAW 49
as Hasselblad, Leica, and Pentax use DNG as their native RAW format. With
the CHDK, you can now join this exclusive club and produce DNG files di-
rectly from your camera.
Using DNG has a few advantages over the native RAW format:
f
You can choose among a large variety of image editors and RAW devel-
opers that accept DNG files as input.
f
DNG files produced by the CHDK do contain EXIF data.
f
Bad pixels are optionally corrected. There are three options in the menu
entry
ALT > MENU > Raw Parameters > Bad pixel removal:
g
Off. No bad pixel removal.
g
Averag. Replaces the bad pixel with an average from its neighbors.
g
RAWconv. The repair job is left to the PC-based RAW converter. The
list of bad pixels is included in the DNG file.
Because bad pixels are optionally considered during the in-camera conver-
sion to DNG, a file badpixel.bin is required by the CHDK. Only then will
the DNG menu items work. So, before using DNG, you must execute the
script badpixel.lua. This script, which is included in the CHDK distribu-
tion, will read the list of bad pixels (as determined by the manufacturer)
from the camera’s firmware. To run the script, switch the camera to Record-
ing Mode and invoke:
1.
Alt > FUNC/SET > Load Script from File… > TEST > BADPIXEL.LUA
2. Press the shutter button. The display will go dark, and the camera will
take two pictures. After 20–30 seconds, the display will reappear and
the camera will wait for input. If the bad pixel test was not successful,
the script will ask you to run the test again.
3. Press
FUNC/SET to save the file.
4. Press
ALT to switch back to normal mode.
5. Now you can go ahead and switch to DNG (
ALT > MENU > RAW Parame-
ters
> DNG Format). Or, you can use the built-in file browser to check
that the file BADPIXEL.BIN has been created in the folder CHDK/
(
ALT > MENU > Miscellaneous Stuff > File Browser).
When working with DNG files, you should also enable the menu entry RAW
buffer cached. The built-in DNG converter will then read the RAW data
directly from memory and not from the card, resulting in faster operation.
However, if you frequently run into memory problems, disable this option.
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