Hdr And Tone Mapping - Canon Camera Hackers Manual

To enable bracketing, you must also set Disable Overrides in the submenu
Extra Photo Operations to Off (section 4.3.1) if you enabled the option
Include AutoISO & Bracketing in the same submenu. Then switch the cam-
era to Continuous mode. On cameras that support multiple shots taken
with the Custom Timer, Custom Timer is another possible option. This would
allow you to predefine the number of shots to be taken.

4.6.2 HDR and tone mapping

High Dynamic Range (HDR) and Dynamic Range Increase (DRI) Photography
have become quite popular among digital photographers. Both techniques
are used for recording contrast ranges that are beyond the maximum con-
trast range of a state-of-art camera sensor [Howard2008][Bloch2007].
Photographic scenes—especially those in full sunlight—can have a dy-
namic range of 16 to 25 Light Values (LV) or f-stops. Even the human eye
cannot capture such extreme contrast (it is limited to approximately 14 LV)
but must adapt itself when looking at dark or bright areas. The eye can do
this because it scans only a narrow area of a scene. The signals produced by
the eye are then processed by the brain, which composes them into a whole
scene again.
The camera does not have this ability. It must record an entire scene in
one step and therefore should be able to capture all the contrast in a scene.
That, of course, is not yet possible. Modern camera sensors can record a
dynamic range of 11–13 LV, a theoretical value that is lowered by noise and
other imperfections. In real-world applications, a camera sensor can cap-
ture a contrast range of 8–10 LV with good quality. When showing an im-
age on an LCD screen, a dynamic range of 5–7 LV can be reproduced, and
when printing an image on photo quality paper, 6 LV is a reasonable as-
sumption.
Because of this situation, you have to decide on the brightness sub-
range that you wish to record—meaning that you must choose the correct
exposure. Brightness values outside that range will record as totally black
shadows and totally white highlights with no detail.
The contrast in the recorded image, which by now is 8–10 LV, must still
be compressed in order to reproduce all details in the image on a print or
on a screen. Typically, this is done in a photo editor such as Photoshop or
Paintshop Pro by modifying the brightness curve. With the CHDK, however,
it can also be done in-camera by using Custom Curves (section 4.3.8). This
tone mapping requires a bit of skill from the photographer; a brightness
curve that is too steep will result in contrasty images with blown-out high-
lights and dead shadows. A brightness curve that is too flat will result in a
flat picture, and vice versa.
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4.6 Bracketing