Flash Bracketing Take a set of images at different flash exposures.


Introduction

The purpose is to create a High Dynamic Range (HDR) image from a set of images taken at different flash exposures. You can also use this script to select the best image from a set of different flash exposures. The first image is taken without flash, the others with flash around the selected flash setting. You can also combine an image with flash and one without flash to create one HDR image (see later).

First the script takes one image without flash. Then the script takes a number of images around the selected flash setting. So if you take 3 pictures, with flash set to center and Flash Step Size=3, it will take the first picture at -1, the second at center and the third at +1. You can later stitch the images together with a program like Photomatix or select the best image.

Make sure that your batteries are fully loaded, because otherwise the delay between the different shots may not be sufficient to fully reload the flash for the next shot. So you may adjust the "sleeps" between different shots to your own needs.

Written for: Canon A640
Also works on: Other Canon AXXX (Not tested)


Parameters (Save as "FlashBracket.txt" file to your /CHDK/SCRIPTS/ folder)

Select P or C mode on your Canon A640.
Make sure that Slow Synchro is On and the flash is set to always On.
Make sure that if you press the Func Set button, the ISO item is selected, but leave the function menu!

• Number of Pics (Default=3)
• Flash Step Size (1/3 EV) (Default=3)
• Initial Delay (Sec) (Default=1)

rem Johan Van Barel 23-07-2007
rem Flash-Bracketing for Canon A640

@title Flash Bracket (Slow Sync, Flash On)
@param a Number of Pics
@default a 3
@param b Flash Step Size (1/3 EV)
@default b 3
@param c Initial Delay (Sec)
@default c 1

if a<2 then let a=2
if b<1 then let b=1
if c<0 then let c=0

print "Pics:"; a, "Step:"; b

sleep c*1000

print "First Pic Without Flash"
rem Set Flash Off
click "up"
shoot
sleep 200

rem Set Flash On
click "up"
sleep 200
click "up"
sleep 200

rem Select +- Flash (Starting from ISO menu)
click "set"
sleep 200
click "down"
sleep 200
click "down"
sleep 200
click "down"
sleep 200
click "down"
sleep 200
for n=1 to (a-1)*b/2
    click "left"
next n

print "Pic 1 of", a
sleep 200
shoot
for s=2 to a
    for n=1 to b
        click "right"
    next n
    print "Pic", s, "of", a
    sleep 800
    shoot
next s

sleep 200
for n=1 to ((a-1)*b+1)/2
    click "left"
next n
sleep 200
click "up"
sleep 200
click "up"
sleep 200
click "up"
sleep 200
click "up"
sleep 200
click "set"

end