in-camera EV+1 - RAW Shooting and Processing - CHDK Forum  

in-camera EV+1

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in-camera EV+1
« on: 05 / May / 2008, 11:35:33 »
I just noticed this neat trick.  I apologize if it is well known already.  I am relatively new to shooting raw in CHDK.

Lets say you have an underexposed image and would like to lighten it up.  If you have saved the raw data you can do this in-camera!  (You must have shot the photo at ISO < 1600 and have a Powershot that has 1600 ISO, like my A720IS).  Do a raw develop, but choose ISO 1600 when you take the shot to trigger the development.  The developed image will have +1 ev.

This works because Canon cheats to achieve ISO 1600.  The raw data capture is the same as at 800.  Just the processing changes to develop at +1 ev.  You can apply this 1600 processing to any raw data using raw develop.

Re: in-camera EV+1
« Reply #1 on: 08 / May / 2008, 07:56:29 »
It's just like taking an already recorded image on your computer, and adjust it's brightness... You don't gain more information (the image is already recorded on a RAW file), you just do a "brightness" function.

It's better to re-take the image instantly then to edit it later, and to avoid using ISO's higher than 100 at all (expect in special cases) :)


Offline DataGhost

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Re: in-camera EV+1
« Reply #2 on: 08 / May / 2008, 08:09:10 »
The camera's LCD is not really calibrated so you might not notice that it needs to be lighter. Also, it's not always possible to shoot another or the same picture again for various reasons. If you have a RAW file you can use the extra data to add a stop of light, which ISO 1600 seems to do. Using this won't add extra noise, at least not any noise you wouldn't get when processing this RAW file on the PC (again, note that it's a RAW file, not a JPEG), because the raw data is inserted after the picture was taken, so it's more than just a 'brightness' function.
This feature is particularly useful when you're not around a computer or something with the necessary post-processing software.


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