Note: This information is now out of date!
I have written an updated blog post here about the new way to enable RAW DNG support with CHDK.
(This blog post is left here for historic purposes. CHDK now has a Create Badpixel.bin feature in the RAW menu so you no longer need to use the badpixel.lua script method listed below to enable RAW support.)
It is possible to shoot RAW images using the new BETA and older Pre-Alpha versions of CHDK on the SD780IS / IXUS 100 IS.
Here is the basic process to enable RAW support with CHDK on the SD780IS:
On the Beta version of CHDK the badpixel.lua script is located in the CHDK/scripts/test folder.
If you are using the the Pre-Alpha Build of CHDK, download the CHDK script badpixel.lua.zip
This file has been modified specifically for use with the Canon SD780IS / IXUS 100 IS camera.
Unzip the archive and copy badpixel.lua into your CHDK scripts folder. Badpixel.lua is a script that makes a map of any bad pixels on the CCD imager. You will have to load and run the script before you can save RAW images.
Turn on ALT mode and load the CHDK Main Menu. The Canon SD780 IS Camera does not have an ALT button so you can simulate the ALT button by quickly tapping the DISP button. The DISP button held for more than 2 seconds acts as the normal DISP button in CHDK.
Open the Scripting Parameters sub-menu.
In the scripting Parameters Menu select Load script from file.
Select BADPIXEL.LUA from the list and press FUNC SET to accept it.
Exit the CHDK Menus.
Switch back to photo mode and then enable the ALT mode.
You MUST be in photo mode for this to work!
When ALT mode is active and you press the shutter button it activates the loaded script and runs it. You have to run this script once before you can then use the DNG RAW image format and save DNG formatted digital negatives.
Press the shutter button to take a photo. It will take quite some time to to take and save the image.
Press the FUNC Set button to save the file. At this point the camera is creating a file called badpixel.bin. This is a map of any bad pixels on the imager. This allows the camera to remove any artifacts caused by bad pixels.
Press the Shutter button to stop the script from running. Turn off ALT mode.
If the file badpixel.bin was not created in the CHDK folder on your SD Memory card you will get an error in Step 4. If this happens, load the SD Memory card on your desktop computer and rename the temporary file bad_tmp.bin to badpixel.bin and continue.
Open the CHDK Menu and then load the RAW Parameters Menu.
Turn on Save Raw.
Turn on RAW file in dir with JPEG
Set Bad pixel removal to Off
Turn on DNG format
Turn on 'DNG" file extension
This will save the Canon CRW raw image in the DNG format. Adobe Photoshop CS4 can now directly open the Canon Powershot SD780IS CHDK RAW DNG files which is quite handy.
You may need a program to convert the DNG file into a format your photo editor can understand such as TIFF or PNG.
You may notice some noise in the RAW images / uncompressed exports. The noise can easily be taken care of by a noise reduction filter such as the "reduce noise" filter. A "median" filter set to 1 pixel could also be used.
Here are a few programs that can convert the DNG formatted images:
Adobe Photoshop CS5
Adobe Photoshop CS5
Process the image.
Here is a sample Canon SD780IS Raw DNG image from the CHDK Beta for you to play with:
Here is an unmodified Canon SD780IS JPEG image taken at the same time to compare against:
I hope this article helps you get more out of your camera. Good Luck!