Copy Sensor Analysis Results

[admin]

Hi Remy,

The Atik camera does not have a variable gain control, so there is only a single, fixed, gain value to make measurements at – that's why you only get a single point on the graph and a single line in the measurement table. That's pretty typical for CCD cameras.

For the difference between 8-bit and 12 bit mode, consider that there are 4096 different possible camera brightness levels in 12 bit mode and only 256 in eight bit mode. When you run the camera in eight bit mode it is very much like taking the 12 bit data and dividing every value by 16 and rounding to the nearest whole number. That means that the e/ADU measurements in 8 bit mode will typically be 16 times bigger than those in 12 bit mode as the ADU levels are 16 times further apart. Also the camera read noise that we so carefully measure in 12 bit mode is almost completely unimportant in eight bit mode. That's because the inaccuracy caused by rounding to the nearest integer eight bit value is much bigger than the intrinsic read noise of the camera sensor. The much higher read noises that appear in 8 bit mode are actually measurements of that rounding error.

Cheers, Robin

[remyastro]

Hi Robin,

Very clear and very intructive! Thank you for your explanations.

I now better understand the importance of well choosing camera gain, offset, exposure and bit depth mode.

My noisy images could actually result from above empirical choices!

Cheers, Remy