I'm using current ASI SDK 0930 with INDI driver with my new 178MC on Rpi3B+ and noticed that my darks/lights/flats have very low ADU values where as bias frames look more like I would expect. Bias frames have median value of around 150 and over depending on configured gain and offset values where as all other frames have mean of only around 4-5 regardless of gain/offset (RAW16 images). Is there a way to disable this automatic "calibration" and just get raw unaltered frames from the camera? Calling ASIDisableDarkSubtract() doesn't seem to have any effect at least
I am not sure what caused the problem of low values on your light image.
But I think it should does not matter with ASIDisableDarkSubtract. We did not have an automatic "calibration" inside our camera. The data you get from our SDK is the raw unaltered data.
According to statistics in PixInsight the median pixel values of each are (as 16-bit data):
Gain was set to 210, offset to 10, raw 16 format. I uploaded a few of the FITS files as http://s2.org/~jpaana/Light.zip if you want to take a look.
I think you should increase your offset. It is too small.
For now, with the time increase, more data is losing, you can find it in the histogram. I think it is the reason why the median value get smaller.
Do you have a suggestion how much the offset should be raised and why the default is only 10 if it clips that badly?
The current one is still not enough.
You can use a software to check histograms of images.
You should add the offset to make sure the histogram like my example. The left side of the wave is complete.
I tried raising offset all the way to 500 (gain still 210) which definitely lifted the range off the left edge for the shorter exposure, but some pixels of the longer one still clip. So the main issue that longer exposures have lower ADU values still remains, even the maximum values, it looks like around 400-500 ADUs have been subtracted from the longer exposure, which causes the low end to clip:
0.01s exposure has minimum value of 176, median 2517 and maximum 6475
1s exposure has minimum value of 4 still, median 1936 and maximum 6015
Both images have similar three peak histogram shapes, but 1s exposure has them at lower values. The fits files are again at http://s2.org/~jpaana/Light3.zip
And i have the same result like you. And the following is our analysis:
1st, for cmos sensor, the Pixel‘s sensitivity is not very linear, expecially at exposure of short time. After 0.7 seconds, this value changes linearly.
2nd, for 178, there are some unknown operations inside the image sensor. This will cause this value to change irregularly. We had asked sony, but they did not answer us.
Anyway, thanks for your time Chad, I hope there still is some better solution, but I think I can live with this for now.