Histogram with a RAW16 Colour Space

johnpd
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Histogram with a RAW16 Colour Space

Post by johnpd »

I was trying to determine a proper white balance for my new QHY5III485c camera using the histogram. I have no issue with the RAW8 and RGB24 color spaces with the histogram set to linear. But for RAW16 I am unable to get enough intensity in the histogram to determine where the three color peaks match. The color lines are almost non-existent. I am pointing at a small white balance card in a daylight well-illuminated room. If I switch to the logarithmic scale, I get a more intense histogram, but is tough to get a single combined peak to work with. Is there any other way I can do this?

JohnD
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Re: Histogram with a RAW16 Colour Space

Post by admin »

Hi John,

could you send a screenshot showing the problem - I think that would help understand what is going on and how to resolve it.

Robin
johnpd
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Re: Histogram with a RAW16 Colour Space

Post by johnpd »

OK Robin,

Here are the two screen prints of the histogram set as linear and logarithmic. I am having a discussion with QHY as to what the correct Bayer pattern is for this camera. The only one that seems to work is GBRG while I was under the assumption that it should be RGGB which is the default for most QHY5III cameras. This is an image of the white balance card I am using to try to find proper white balance.

JohnD
QHY5III485C_RAW16_GBRG_Linear_Hist.jpg
QHY5III485C_RAW16_GBRG_Linear_Hist.jpg (305.75 KiB) Viewed 538 times
QHY5III485C_RAW16_GBRG_Log_Hist.jpg
QHY5III485C_RAW16_GBRG_Log_Hist.jpg (331.11 KiB) Viewed 538 times
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Re: Histogram with a RAW16 Colour Space

Post by admin »

Hi,

to me, your colours look wrong - I can see a purple cast to the white areas and a grid pattern in the image which are usually signs of the wrong bayer pattern being used. You will find that 2 patterns give you the grid + purple cast, one gives correct colours and the other gives the red/blue channel swapped. Sometimes the easiest thing to do is to point the camera at something red and then pick the option that makes the image red.

The logarithmic histogram is probably quite confusing because of the different things in view of the camera each contributing to the histogram. Use the selection area option to take a histogram of a smaller area of the image to help clear this up (Item 11 in this diageam - https://docs.sharpcap.co.uk/3.2/#The%20Tool%20Bar)


Robin
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Re: Histogram with a RAW16 Colour Space

Post by johnpd »

Hi Robin,

Thanks for your reply. I did a little more testing. I found out that if I have Blue or Red set at about 200 or more in linear mode, then the histogram basically disappears. I tried (again in RAW16) all the various Bayer options and this is what happened to the histogram when adjusting colors:

Bayer=RGGB:
  • Adjusting Red actually adjusts Green
  • Adjusting Green adjusts all colors
  • Adjusting Blue adjusts Green
Bayer=GRBG:
  • Adjusting Red actually adjusts Blue
  • Adjusting Green adjusts Green
  • Adjusting Blue adjusts Red
Bayer=BGGR:
  • Adjusting Red actually adjusts Green
  • Adjusting Green adjusts all colors
  • Adjusting Blue adjusts Green
Bayer=GBRG:
  • Adjusting Red actually adjusts Red
  • Adjusting Green adjusts Green
  • Adjusting Blue adjusts Blue
So it would seem that GBRG is the proper pattern. But I was not able to get proper color balance. I tried a red folder and had no luck no matter what I tried. And again if I raised Red or Blue too high the histogram lines basically disappeared in linear mode. I am beginning to believe this might be a QHY driver issue. The only response I got from QHY was a couple of days ago and the responder said he was pushing this to someone higher up for a fix. He did not say what was wrong or what the fix involved.

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Re: Histogram with a RAW16 Colour Space

Post by admin »

Hi John,

one more thing comes to mind...

Does this camera have strong sensitivity in the IR? Some cameras do, and if you do not have an IR block filter in place then they will give a pink/orange colour to everything no matter how you adjust the balance. Colour cameras sometimes have an IR block in the glass over the sensor, but some do not. Worth checking the specs for the camera.

Robin
johnpd
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Re: Histogram with a RAW16 Colour Space

Post by johnpd »

Hi Robin,

No this camera comes with a UV/IR cut filter.

JohnD
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Re: Histogram with a RAW16 Colour Space

Post by johnpd »

Just an update. QHY is aware of the issue. I don't know when they will have a resolution.

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Re: Histogram with a RAW16 Colour Space

Post by admin »

Hi John,

thanks for sharing that info.

cheers,

Robin
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Re: Histogram with a RAW16 Colour Space

Post by johnpd »

OK, I got a new driver from QHY and it appears to work. I was able to get RAW16 to a pretty good white balance. When I did a snapshot, I had the save file type option as TIFF. Of course the output image was in grayscale. Is there a way to convert that to RGB or do I need to save it as a FITS?

JohnD
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