Wednesday, January 1, 2014

Handheld Bracketing w/ CHDK

If you followed this (young) blog, you may know that the first ever post was about handheld HDR using the very fast 11fps of the Lumix LX7.

Lately, I kept myself busy with Canon stuff, in particular the CHDK and cheap P&S cameras. For purpose of experimentation, I bought an IXUS 140 (aka ELPH 130). The 140 is a cute little camera I really like, very pocketable, CHDK, although ALPHA, works as a charm!
The cheap chap that I am, I only afford the camera with a really old Sandisk Ultra II 2GB SD-card. I am sure that there are faster cards available... however, this is what was sitting unused in my desk's drawer, hence, that is what I use(d).

The drawback of using an older generation SD-card is of course the speed in which data can be written to it. In particular when saving data in RAW, this plays a major role.

For matters of experimentation, I took the camera, set CHDK to bracketing in continuous mode and took some shots. Photomatix was used to create the DHR images.

The first HDR image that I would like to share is a shot in which I used 3 frames recorded as DNG (which is essentially raw data). The middle frame was shot with -1 Ev. Lens distortion correction was applied to the final image using RawTherapee.
3 DNGs - lens distortion correction using RawTherapee
If you look closely, the branches in the center of the image display some ghosting. It was a windy scene and I did not go through any major anti-ghosting procedure.

The second shot is an HDR image using 5 JPG frames. Again, the middle image at -1 Ev.
No geometrical correction applied here, mind you, the camera's firmware does something already when recording JPGs... something that actually over compensates at wide angles.
5 JPGs - no correction, note that the camera itself over compensated
Here you have it, even a slow and inexpensive camera can be used for handheld HDR photography. 3 frames in RAW (or DNG) or 5 frames in JPG, w/o a tripod, both demand a very calm hand...
In this shot, I used the anti-ghosting tool of photomatix on the approaching tram.

Here is how I do it, inspired by Discovery Channel reporting about snipers:
  1. calmly prepare your camera, making sure all the setting are correct, e.g. exposure compensation
  2. stand firm on both legs, feet at shoulder width
  3. breath slowly but steadily, wait until you body settles
  4. hold your camera with both hands
  5. press your arms against your chest
  6. relax
  7. breath in deeply
  8. exhale slowly half pressing the shutter release
  9. when your chest is relaxed and your lungs exhaled, gently press and hold the shutter release
  10. freeze (not thinking about it!)
  11. hold your breath and wait until your camera recorded the 3, 5 or 7 frames you need.
Step 11 may actually take some time, training increases the time you can hold your breath w/o moving.

All in all, handheld HDR photography remains a challenge. It is best done with a fast bracketing camera, such as the Lumix LX7, however if the camera at your disposal is somewhat slower, there is still hope!

Record photons!

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