CHDK on an Ixus 750

While on paternity leave I have been playing around with my Canon Ixus 750 digital camera. Primarily I have been doing macro (close-up) shots of insects etc., but I also wanted to experiment with other kinds of photography, e.g., High Dynamic Range images (HDR). In HDR you take pictures of the same scene at different exposure levels, and after that a computer program stacks these images to create the HDR image. When taking such pictures it is vital that you do not move the camera, which can be quite hard even if you have a stand for it. I was therefore looking for a software solution to HDR, that would automatically take 3 to 5 pictures at different exposure levels for me, so that Idid not need to touch the camera in between shots.

For that I installed CHDK on my Ixus 750 and I must say that I am impressed. Using the CHDK firmware extension a horde of new features are unlocked (for example the possibility to take RAW images instead of JPEGs). And most importantly CHDK is scriptable, so you may write your own scripts to control your camera.

Based on an example in the tutorial I quickly wrote an HDR script that works on an Ixus 750. When I activate this script my camera snaps five pictures at -2, 1, 0, +1, +2 exposure.

@title EXP bracketing 
@param a Number of +/- steps 
@default a 2
@param b Step size (1/3EV)
@default b 3

if a<1 then let a=2
if b<1 then let b=3

sleep 1000

print "Preparing..."
rem click "erase"
for n=1 to a*b
    click "left"
next n

click "shoot_half"
sleep 3000
for s=1 to a*2
    print "Shoot", s, "of", a*2+1
    click "shoot_full"
    print "shot done"
    sleep 5000
    for n=1 to b
        click "right"
    next n
next s

print "Shoot", a*2+1, "of", a*2+1
click "shoot_full"
sleep 5000

print "Finalizing..."
for n=1 to a*b
    click "left"
next n
rem click "erase"

end

In order to use this script the camera must be in manual mode and the exposure menu must be opened...