Nonzero LSBs with RAW16 from ASI178 with Linux driver

nerdenceman

I was inspecting pixel values from my ASI178MC in RAW16 format and I noticed that the two least significant bits (LSBs) were not always zero. This is unexpected, since the ADC resolution of this camera is (at most) 14 bits. On further investigation, I found that this only happens when I capture on Linux but does not happen on Windows.

Here are histograms showing the frequency that each bit is set. For each stem, a value of 1.0 would mean the bit in that position is set (equal to 1) in every pixel in the frame, and a value 0.0 would mean the bit in that position is never set (always 0).

In the Windows capture, as expected, the values of bits 0 and 1 (the two LSBs) are always zero, leaving 14 bits of actual data from the sensor. In the Linux case, bits 0 and 1 are not always zero. I wonder if perhaps there is a bug in the Linux version of the driver where the two LSBs contain uninitialized data?

I used ASICap for this experiment on both Windows and Linux, from ASI Studio version 1.6.3 downloaded and installed today.

Software@ZWO

Hi nerdenceman, please set the white balance to WB(R) = 50 and WB(B) = 50 and retry. Thank you.

nerdenceman

Thanks for the quick response! I retried with white balance settings set to 50 on Linux and now see that the two LSBs are always zero.

A couple of follow-up questions:

What's the exact operation performed when ASI_WB_R or ASI_WB_B are set to values other than 50? Is there a formula?
What is the rationale for the default values? It seems that ASI_WB_R defaults to 70 and ASI_WB_B defaults to 90.

Thanks

Software@ZWO

nerdenceman Hi nerdenceman, when ASI_ WB_ R and ASI_ WB_ When B is 50, we will not do white balance processing on the image.
For color cameras, we will give a default white balance value, and under this default value, the image will get a better color.