Moon image is green.

[LaurenceT]

Up until now I've been using an Evoguide 50ed with an Asi224mc and uv/ir cut ZWO filter and the resulting images have not been green.

Last night I just changed to a different refractor and the images were all green.

I'd be grateful for any ideas why this should happen and what I can do about it. Thus far I've simply removed the green colour in my image manipulation application.

Images taken using Sharpcap.

[Elp]

Typically in an RGGB Bayer matrix pattern there are two (50 percent) green pixels to the one (25pc and 25pc) of red and blue. So the general trend is the image will turn out green as those pixels are more abundant and will receive the most broadband light. In AP processing you normally have to align the RGB channels or do a green noise removal operation to get a "normal" coloured image. In your tests, did you do a like for like test (same target, exposure length, total imaging time etc). I suspect the refractor is receiving more light due to the aperture increase.

[vlaiv]

7 minutes ago, Elp said:

Typically in an RGGB Bayer matrix pattern there are two (50 percent) green pixels to the one (25pc and 25pc) of red and blue. So the general trend is the image will turn out green as those pixels are more abundant and will receive the most broadband light. In AP processing you normally have to align the RGB channels or do a green noise removal operation to get a "normal" coloured image. In your tests, did you do a like for like test (same target, exposure length, total imaging time etc). I suspect the refractor is receiving more light due to the aperture increase.

That is really not the reason why images turn out green

It does nothing to do with number of pixels - but with relative sensitivity in different parts of spectrum.

Most sensors have strongest QE in green and this will result in green cast if image is not color corrected (often wrongly referred as white balance). Some cameras have peak in red part of spectrum (usually those very sensitive in IR) - and those produce reddish tint images.

@LaurenceT

You have "white balance" controls in your capture software which you can tweak to get color neutral image. Alternatively - do color balance afterwards in software while at processing stage.

 

[LaurenceT]

Just now, vlaiv said:

That is really not the reason why images turn out green

It does nothing to do with number of pixels - but with relative sensitivity in different parts of spectrum.

Most sensors have strongest QE in green and this will result in green cast if image is not color corrected (often wrongly referred as white balance). Some cameras have peak in red part of spectrum (usually those very sensitive in IR) - and those produce reddish tint images.

@LaurenceT

You have "white balance" controls in your capture software which you can tweak to get color neutral image. Alternatively - do color balance afterwards in software while at processing stage.

 

Yes, I should have corrected it in white balance, thanks.

[Elp]

19 minutes ago, vlaiv said:

Some cameras have peak in red part of spectrum (usually those very sensitive in IR) - and those produce reddish tint images

But the 224mc is mostly QE in red first, closely followed by green?

I understand the CC part, histograms usually come into alignment after curves/GNR/CC operations.

[vlaiv]

17 minutes ago, Elp said:

But the 224mc is mostly QE in red first, closely followed by green?

Indeed it is.

There are a few possible explanations.

- funny white balance settings in the capture app (set to auto but failing to do its thing properly for example).

- wrong order of bayer matrix elements while red being stronger as per QE.

Bayer matrix order is usually something like this:

RG
GB

But if there is change in software or drivers - image can be read out backwards (bottom to top instead of top to bottom) - which changes order of bayer matrix - it flips it in vertical so it becomes

GB
RG

With normal - "green strong QE" cameras, this produces sort of pinkish tint because two green pixels (which usually have the same / very similar value as they are adjacent) turn into R and B - with the same levels and that becomes dominant thing, but with R being stronger - this inversion can make green image

- very strong luminance cutoff filter like L3 filter used. Since it removes outer parts of spectrum (blue and red sides of spectrum) - it effectively removes "volume" in these colors or surface under the QE curve that is actually what counts towards total color weight (peak QE is good indicator only if three component cover roughly the same wavelength ranges).

[ollypenrice]

56 minutes ago, vlaiv said:

That is really not the reason why images turn out green

It does nothing to do with number of pixels - but with relative sensitivity in different parts of spectrum.

Most sensors have strongest QE in green and this will result in green cast if image is not color corrected (often wrongly referred as white balance). Some cameras have peak in red part of spectrum (usually those very sensitive in IR) - and those produce reddish tint images.

@LaurenceT

You have "white balance" controls in your capture software which you can tweak to get color neutral image. Alternatively - do color balance afterwards in software while at processing stage.

 

Agreed. I don't find any difference in green noise or balance between OSC and mono captures.

If the image really is strongly green then an incorrect debayer is very likely.

Olly

[ONIKKINEN]

12 minutes ago, ollypenrice said:

Agreed. I don't find any difference in green noise or balance between OSC and mono captures.

If the image really is strongly green then an incorrect debayer is very likely.

Olly

I think your very dark skies are to thank for the ease of use, since most broadband light pollution is strongest somewhere in the green to yellow range. All my OSC images are strongly green under SQM 20.77->21.35 skies.

This is with an IMX571 sensor, which has significantly less QE for blue and red compared to green.

[Clarkey]

You are all wrong. Mr Musk has had the moon painted green so we stop moaning about his satellites😀