Images appear black and white instead of color

Discussion of using SharpCap for Deep Sky Imaging
Moonstruck
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Images appear black and white instead of color

#1

Post by Moonstruck »

I have a new Skywatcher Esprit 100 telescope and ZWO asi 294 color (cooled) camera. Last night I tried imaging for the first time using EQMOD, Stellarium and Sharpcap Pro, with M57 (the ring nebula) as the target. When I was imaging in Sharpcap, the image appeared in color on my laptop screen, but when I looked at the stored images (png files) afterwards, they were all black and white. I then tried to process them in GIMP to try to bring the color out, but nothing worked- I tried curve stretching and several other settings with no luck.

Any idea why the saved png images are all black and white? I have attached my imaging session details below if that helps in your response. I also tried to attach a png file, but it was too big to upload.

[ZWO ASI294MC Pro]
FrameType=Light
Debayer Preview=On
Pan=504
Tilt=0
Output Format=PNG files (*.png)
Binning=1
Capture Area=3104x2822
Colour Space=RAW8
High Speed Mode=On
Turbo USB=80
Flip=None
Frame Rate Limit=Maximum
Gain=460
Exposure=5.330s
Timestamp Frames=Off
White Bal (B)=83
White Bal (R)=49
Brightness=12
Cooler Power=0
Temperature=4.1
Target Temperature=5
Cooler=Off
Auto Exp Max Gain=285
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Background Subtraction=Off
Planet/Disk Stabilization=Off
Banding Threshold=35
Banding Suppression=25
Apply Flat=None
Subtract Dark=None
Display Black Point=0.172700309678545
Display MidTone Point=0.529980894476162
Display White Point=1
Notes=
EQMOD ASCOM HEQ5/6=RA=18:53:40,Dec=+33:01:28 (J2000)
TimeStamp=2022-04-11T06:17:11.1429897Z
SharpCapVersion=4.0.8667.0
StartCapture=2022-04-11T06:17:08.7162159Z
MidCapture=2022-04-11T06:18:09.5532159Z
EndCapture=2022-04-11T06:19:10.3899650Z
Duration=121.674s
FrameCount=20
TimeZone=-4.00
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admin
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Re: Images appear black and white instead of color

#2

Post by admin »

Hi,

your saved files are in RAW format, so the colour is encoded in the different pixel values of neighbouring pixels. You need to debayer the image files to see the colour. See this thread for more info : viewtopic.php?t=254

BTW, you will probably want to switch into RAW16 rather than RAW8 for deep sky - you will find the images are much better in the long run.

cheers,

Robin
Moonstruck
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Re: Images appear black and white instead of color

#3

Post by Moonstruck »

Ok, thanks. So I have to "debayer" each time I process, correct (before using deep sky stacker)? Or is there some setting I can change in Sharpcap to avoid having to debyer every time?
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Re: Images appear black and white instead of color

#4

Post by admin »

Hi,

if you save to FITS format, then you can persuade DSS to do the debayer for you - there is an option in the FITS Files settings in DSS to turn this on. As far as I know, DSS only has this ability for FITS files, not TIFF etc.

cheers,

Robin
Moonstruck
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Re: Images appear black and white instead of color

#5

Post by Moonstruck »

Thanks Robin. I imaged M51 last night (FITS, raw 16 bit files), and used deep sky stacker for stacking. But when I processed the stack in GIMP, the final image came out black and white. Here is what I did. As you mentioned, in dss there is an option (in the "options" section) for "RAW/FITS DDP settings." In the "FITS" tab in that section, I checked the box for "monochrome 16-bit FITS files are RAW files created by a DSLR or a color CCD camera." However, that didn't work. Is there anything else I should have done to get color images? Maybe another box to check in dss?

That said, I had another thought... maybe the color issue has nothing to do with deep sky stacker, but rather, GIMP... I am new at this and don't know much about GIMP processing, or how to get color images to appear. Should I be using another more user-friendly processing program? If so, can you recommend one good for beginners? Startools, astropixel processor, other??

Here is the link to the raw stack (after using dss), in the event you need to see what it looks like. Maybe you can take a quick look and tell me if you are able to process it in color?? Any guidance will be very appreciated!

https://drive.google.com/file/d/1pvZFMD ... sp=sharing

Thanks,
John
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turfpit
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Re: Images appear black and white instead of color

#6

Post by turfpit »

John

This is your stacked image loaded into FITS Liberator. The image data shows 3 planes (R, G, B). This indicates that the file has been debayered (the colour restored).

FITS_Liberator.JPG
FITS_Liberator.JPG (52.64 KiB) Viewed 3391 times


If you load this image into GIMP (or similar software) it will open 3 windows which correspond to the 3 (RGB) planes shown above. The way round this from DSS is to do a Processing > Save picture to a file and save as a TIFF (16 or 32-bit) rather than use the autosave file. GIMP can now handle the TIFF file and display colour.

This is your stacked image loaded into PixInsight (or Siril). The image has a green background ( M51 coloured) which suggests the debayer pattern is incorrect.

stack_in_PixInsight.JPG
stack_in_PixInsight.JPG (42.08 KiB) Viewed 3391 times


There are 2 places where this can go wrong:
  • SharpCap 'Save' setting
  • DSS RAW/FITS setting

SharpCap Save settings. Look at File > Sharpcap Settings > Save tab. If the wrong item is checked, this needs rectifying for future imaging sessions.

SC_save_settings.JPG
SC_save_settings.JPG (94.53 KiB) Viewed 3391 times


DSS setting. Look at Options > RAW/FITS. If this is set to the default of RGGB then try restacking in DSS with GBRG. Don't forget to 'save as' TIFF.

DSS_setting.jpg
DSS_setting.jpg (36.12 KiB) Viewed 3391 times


Let us see what comes out of this. When doing any restacking, test with say 10 light frames - that will be enough to see if the right debayer pattern is being used.

It might be worth posting your equivalent settings for the above pictures, plus the camera settings file if you need more help with this. FITS Liberator is a free download and a 'must have' for investigating FITS related issues.

Once this issue is resolved we then need to check that both the above settings are correct for future image processing to work smoothly.

Dave
Moonstruck
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Re: Images appear black and white instead of color

#7

Post by Moonstruck »

Robin, I changed the default Sharpcap settings to "SER" and "FITS" files like you said, and hopefully that will fix the problem. I won't know until I image next time (hopefully soon).

I also tried choosing GBRG in dss, and re-stacking with only 10 light frames, and saved the final stacked file as a TIFF file. Then I opened it in GIMP, but instead of GIMP showing a greenish image, it had a purple tone. I also did an internet search, and from what I can gather (from other people's comments on-line) the pattern for my camera (ZWO asi 294 MC color-cooled) is RGGB. So I don't think the problem was the color coding.

I have another (possibly un-related) question. You may have noticed the really bad horizontal banding in the image. Any idea what that is caused from? What is usually the cause of banding such as this? Would using the improper Sharpcap settings possibly cause this? Or could it have something to do with the calibration frames I used (flats, darks, bias)? I used a white T-shirt stretched across the telescope lens for the flats, with a lamp shining into it... might that be the problem?

Note- I also have a question on use of the histogram for imaging, but I'll address that separately in another post, to avoid confusion.
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turfpit
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Re: Images appear black and white instead of color

#8

Post by turfpit »

John
the pattern for my camera (ZWO asi 294 MC color-cooled) is RGGB
The pattern is interpreted by how the processing software reads the colour matrix - when ROWORDER = TOP DOWN or BOTTOM UP. For example:

RG
GB
RG
GB
RG
GB

The pattern would be RGGB if read from the top down or GBRG if read from the bottom up.


I don't think the problem was the color coding
There are 4 combinations RGGB, GRBG, BGGR, GBRG - worth trying the other 2 and see what happens. One of the combinations will give the correct colour.

The other information I requested will throw some light on this.

Dave
Moonstruck
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Re: Images appear black and white instead of color

#9

Post by Moonstruck »

Thanks Dave. As you can see I am new at this! Good to know the pattern being read has to do with the software, not the camera.

I was also hoping you could help me figure out where the bad horizontal banding is coming from (as seen in above pictures). No idea what the cause is. If you can advise on that I’d really appreciate it! Note- I tried processing just a single light frame and the banding was still there. So I think it may be something I am doing during capture. My asi 294 is cooled so not sure if the voltage for that may have caused it. I cooled it to -10 C during capture. And my gain was at 120, if that helps. Thanks.
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turfpit
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Re: Images appear black and white instead of color

#10

Post by turfpit »

John

Did you try to stack 10 frames with the other 2 bayer combinations?

This is how I got to grips with debayering and my ZWO ASI120MC camera. Carry out the test against a land based object. The 4 results are correct colour with no grid pattern, incorrect colour with no grid pattern and 2x mono with grid pattern.

ASI120MC-Bayer-pattern-test.pdf
(953.9 KiB) Downloaded 75 times


Try holding down the control key while connecting the camera in Sharpcap. This will put all the camera settings back to default.
As you can see I am new at this
I have been at this for about 6 years and have experienced everything you are going through.

I suggest you raise a new topic for the banding problem as it is buried under an 'images appear black and white' heading.

Dave
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