How Can I Use ImageCalibration Without Clipping Black Pixels?

[BenKolt]

Greetings!

I have a situation where I'm trying to calibrate H-alpha frames, but standard use of ImageCalibration (IC) clips some of the pixels to black.  The dark histogram overlaps enough with the light frame histograms to cause this issue.

I've devised a nice, suitable way to avoid this using PixelMath (PM) for my calibration rather than IC.  In PM, I simply use the formula: ($T - D)*mean(F)/F + (56/2^16), where D is the master dark and F is the master flat, and the latter term being a pedestal of 56 ADU that is added after the calibration math, which is enough shift to avoid negative values.  I then place my raw files in an ImageContainer and run the PM process on the container.  I've defined the calibrated output to be collected in the directory of my choice.  This performs the identical operation as ImageCalibration but adds the pedestal.

But I'm curious if I am overlooking a way to do this with ImageCalibration?  I see there is the Pedestal option, but that's for performing a subtraction on the raw image files and (I think) calibration files prior to calibration.  This doesn't help me clip the negative values.

Thanks for your help!

Best Regards,
Ben

[pfile]

output pedestal (in the output files section) should take care of this. you shouldnt have to resort to pixelmath, it is a common problem.

rob

[BenKolt]

Thanks, Rob!

Good grief!  How did I miss that?  I was fixated on the Pedestal Section right below it that I overlooked the Output Pedestal value.  That should give me exactly the same results as my PixelMath solution.  I figured there had to be an input for this somewhere as it's a common issue.

Ben

[pfile]

it is kind of confusing; especially since pedestals are somewhat advanced in nature it's probably never been talked about too much in tutorials, etc.

rob