[Alt-photo] Re: sensor and curve

[etienne garbaux]

jusdado wrote:

>But someone could draw or define the "characteristic curve" of a 
>digital sensor?. The digital sensor has a linear response to 
>increases in exposure. There would be "heel", not "shoulder", just straight?

You appear to be asking for a curve relating the light falling on 
digital sensor pixels to the digital code produced from those pixels.

The answer is complicated, because unless you design and build your 
own camera, you will always be dealing with pixel values that have 
had substantial post-processing done on the "raw pixel" data by the 
processing engine in the camera.  These days, a significant amount of 
image processing is done right on the sensor chip, so it is very hard 
even to define what the term "raw pixel data" means -- it may not 
even be accessible external to the sensor chip.

So, as always, the answer is: test, test, test.  Plot the response of 
your own cameras.  But note that in-camera processing engines often 
respond dynamically, so the output data of any particular pixel to a 
certain quantum of light is very likely to depend on the quanta of 
light falling on all of the other pixels on the sensor.

Best regards,

etienne