Orchid XP v8 wrote:
> Jim Henderson wrote:
>> On Wed, 05 May 2010 12:35:02 +0200, scott wrote:
>>
>>> And typically pros will not let the camera do *any* processing, and
>>> import the raw sensor data to their computer for manual colour,
>>> sharpness and exposure control.
>>
>> Exactly - the adjustments I made were pretty basic with GIMP (similar
>> to the ones you made), but if RAW format images were available,
>> there'd be a lot more room to adjust things like exposure.
> 
> ....but once the image has been taken, the exposure has already
> happened. How can you change it after the fact?
> 

When shooting in RAW, the camera is not recording 'this pixel is X
amount of green.' It is recording only 'sensor location x,y received Z
amount of light.' The editing software looks at that, not at the
interpolated (RGB,HSL,HSV,CMYK,whatever) image. So, if you know that Z
light was received over T time, and you want to know what it might look
like had you left the shutter open for 1.5T, just go through and bump
everything to 1.5Z, then interpolate to get the image to display. This
gets much less accurate as you get past one full step exposure, 0.5 and
2 times the light.

This still won't recover data from areas that were saturated, as if the
sensor is all at Zmax they will all reduce equally. It can, since there
often there is some light hitting the sensor at all locations, be used
to push an exposure up and get more detail out of dark areas. You can
also change the curve of the sensor response by group, affecting only
the red, green, or blue sensors. You can do this with a JPEG as well,
but my suspicion is that if you use a RAW the curve would be applied
before the sensor elements are interpolated.

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