Green cast to images when using autostretch

[Ias]

Hi all

I'm a Sharpcap newbie so this may be a dumb question

I am imaging using a ZWO 294MC Pro camera through a 90mm triplet. I have produced some good images so far, and like using Sharpcap.

I also do some outreach and EAA. However, I'm having an issue with producing a colour balanced image on screen in Sharpcap. When I hit "auto stretch" to make the preview panel nicely visible, it acquires a green cast to the image. I'm aware this is probably because the camera is more sensitive in the green.

My question is this: Is there a way to easily get the preview image to stretch such that a colour balanced stretched image is displayed? This would really help me when using the (excellent) live stack feature for EAA.

Thanks

Ias

[admin]

Hi,

if you are using live stacking then as well as the auto-stretch button, there are auto colour balance buttons that will try to balance the R/G/B channels of the stack - one uses the background brightness as a guide, the other uses star colours - sometimes one works better than the other. You can also make manual adjustments too - see https://docs.sharpcap.co.uk/4.1/#Histogram%20Tab

Another approach to consider is to use one of the 'Background Subtraction' modes in the 'Preprocessing' control section on the right - probably 'Blended Offset' is the best. This tries to remove the skyglow background from each image. A combination of this skyglow (particularly if it is relatively white from LED light pollution) and the green sensitivity of the camera can cause the issue you are seeing. This approach may help without needing to use live stacking, but can also be used with live stacking.

Hope this helps,

Robin

[Ias]

Thanks Robin, I'll try that.

Phil

[jonstarrysky]

Just a minor comment to add and possibly not relevant to this thread (as Robin suggests, a simple answer is open the Histogram Tab of the Live Stacking work area if not already open, and hit the auto-colour balance button which is the lightening icon, just under the red slider.

FWIW, if you image a pure white surface illuminated with ambient daylight with the 294MC and look at the smart histogram, the green curve is about double the intensity of the red and blue curves (I can post a screenshot if interested). So the 294MC camera seems green biased, I think due to the bayer matrix incorporating more green sub-pixels that red or blue. My understanding is the rationale for that design is the human eye is more senstive to green wavelengths and this is being emulated. But when we hit auto-colour this lines up the R,B,G curve peaks, hence the raw data being green-biased seems a bit of a waste of time....