What The Chdk Can Do For You - Canon Camera Hackers Manual

The CHDK adds an additional task that manages the CHDK functions. In
addition, the CHDK needs hooks in the native tasks to communicate with
them. Therefore, the CHDK loader embodied in the file DISKBOOT.BIN per-
forms the following steps:
Copies the core CHDK code into a suitable memory location within the
f
camera. Of course, this is only possible if the camera has enough free
memory. On some cameras this is not the case, and limited or no CHDK
support is possible.
Restarts the camera with the CHDK code as the entry point. Instead of
f
the native boot process, the CHDK boot process is now performed. This
process will:
Launch the CHDK task.
g
Add hooks to the native tasks (logging task, keyboard task, image-
g
capturing task, file-system task) while loading and launching those
tasks.
In this way, the changes applied to the native firmware are only temporary
and remain minimal. Unfortunately, the position of the hooks is different
for every firmware version, so a different CHDK version is required for each
firmware version. The main task of migrating the CHDK code to a new
camera is to find out the correct position of the required hooks (section A.4).

2.3.3 What the CHDK can do for you

RAW images
One of the most outstanding functions of the CHDK (and historically the
first) is the ability to deliver and process RAW sensor data. The popularity of
RAW image processing relies on the fact that RAW files contain the full in-
formation gathered by the sensor. The JPEG format, in contrast, resamples
the 10-, 12-, or 14-bit pixel values down to an 8-bit scheme. This can result
in washed-out highlights. PC-based RAW converters, on the other hand, are
able to recover at least some of the blown-out highlights.
An additional problem with the JPEG format is interpolation. Sensor
cells responsive for red, green, and blue light are placed side by side. There-
fore, interpolation is required to compute a complete pixel value as re-
quired by the JPEG format. PC-based RAW converters (section 4.5.4) can do
a better job than the tiny processor within the camera, resulting in im-
proved sharpness and fewer artifacts such as moirés.
Another advantage of the RAW format is that processing decisions, such
as white point and color space (e.g., sRGB, AdobeRGB), can be postponed
until the image is in the development phase on the PC. There, the photo-
grapher can try out different settings without risking loss of image detail.
2.3 The CHDK: What it is and how it works
Figure 2-2
The CHDK main menu organizes the
numerous functions into 11 groups.
The menu is obtained by changing into
<Alt> mode
the MENU
7
(chapter 4), then pressing
button.