6 replies to this topic

[Thomas24]

I have been deep sky imaging for many years, using my canon rebel t3i and a Celestron mount. I have had very good luck with this setup.  Now I moved up to a Zwo asi585 camera and the am5 mount. The images I have Ben getting with this setup is quite impressive.  Just for fun I put my canon camera on my AT72 and started taking images .  The images I got looked very good but they all have a green tint to them. I played around with white balance and had no luck. I just started thinking that the older images are jpeg and they stacked well.  The new images are fits because the Asiair plus needs this formate for the camera. All of my new images are saved on my iPad, but the green tint is there. Could it just be the file format?  Any help would be very appreciated. Thanks.

[sharkmelley]

JPEG images from your Canon camera have been automatically bias-subtracted, white-balanced and then non-linearly transformed into a non-linear colour space - typically sRGB but sometimes AdobeRGB.   None of this processing is done to the FITS files that ASIAIR creates from the Canon camera. 

[vidrazor]

If you've been processing your stuff in Photoshop, Lightroom, GIMP, etc. you're going to have to move to a dedicated astro image processor. You can get something like Astro Pixel Processor or PixInsight, or try out the freebie Siril, which is what I use, and has processes to remove the tint you're seeing with Phtometric color calibration and remove green tint processors, as well as other tools to help you bring out your image. A quick tutorial can be found here.

[james7ca]

A green bias is not unusual when processing RAW images from a one-shot-color camera. There are ways to correct for this but it depends upon your processing software. Under MS Windows and with a program that can run Photoshop plug-ins you can try the following free software:

 

  https://www.deepskyc...ista-Green.html

Edited by james7ca, 21 November 2023 - 01:42 AM.

[Thomas24]

Thank you one and all.  Your responses game me the info I was hoping for.  HLVG worked great and solved my problem. Thanks James.

[sharkmelley]

HLVG worked great and solved my problem.

You should check this out by taking a quick image of a terrestrial scene (or object) with many different colours in it.  Does HLVG work great for such a scene?  Or does it lead to distorted colours?

 

Your initial problem (green stars) is almost certainly an issue of white balance.  The data straight from the sensor is usually very green because the sensor has a greater response to green wavelengths then to red and blue.  White balance (not HLVG) is the usual response to this and is a fundamental part of every astro-processing workflow.

[vidrazor]

Thank you one and all.  Your responses game me the info I was hoping for.  HLVG worked great and solved my problem. Thanks James.

I take it you're not using an astro specific app to process your data. That's not the best approach