Nikon D750 DSLR takes only black and white images


#1

Used SGP for the first time last night and noticed the resulting .FITS light images are black and white only. E.g. https://www.dropbox.com/s/uchiqfhurtufxqd/Antares%20HIP80763_30sec_1x1__frame8.fit?dl=0

Why is the colour missing? The only settings I can see in SGP for my Nikon are FITS and 1x1 AF Binning, which were the defaults.

  1. I connected the Nikon camera
  2. Ran the sequence with several repeats, ISO 1600.
  3. The .fits files were generated as expected, but were greyscale only?

#2

SGP captures and displays the raw data as it comes off the camera, where each (monochrome) pixel is covered by a colour dye, allowing them to capture the amount of red/green/blue light. From each four adjacent pixels two are covered with a green dye, one with red and one with blue. If you zoom into the image in SGP you will see the grid pattern caused by this. Your image processing/stacking application will convert the raw images to color when calibrating and stacking using a process known as debayering. Unfortunately SGP doesn’t do this for preview purposes.


#3

Yes I noticed the grid pattern in the photos and was curious about that. I’m still confused however. My understanding is that a .fit/.nef raw file can be in one channel (mono) or have all rggb channels (colour). I’m expecting SGP to be creating colour images from my Nikon, just like e.g. Backyard Nikon does. I’m not using filter wheels.

I understand that when processing colour .nef images from my Nikon (e.g. captured via Backyard Nikon) in Pixinsight I have to tick the debayer option. All one shot colour camera images need to be debayerred. My Nikon is a one shot colour camera. I was expecting to be following the same workflow with SGP. But SGP is creating one channel (mono) from my OSC Nikon. Please examine my previously attached .fit file to see what I mean. Surely SGP supports creating OSC .fit files?

Sorry if I am missing something!


#4

There is a difference between true monochrome and Bayered images (which are grayscale). SGP does not do any debayering. As such all images viewed in SGP will be grayscale. However OSC images will always have color data associated with them. If you open up PI and debayer the images you will indeed get color from a “single channel” OSC image. SGP does not output 3 channel (Red, Green Blue) FITs as they would be 3x the size (and are honestly obnoxious to process…)

If you would prefer to work in NEF rather than FITs, SGP can save off the untouched .NEF files as well. Just choose the NEF option in the Nikon Settings Dialog.

Might help to better understand how “OSC” cameras actually work. The CCD/CMOS itself is a monochrome sensor (technically it reads light levels and not color…but let’s not go there). On top of the sensor is a Bayer Matrix which consists of pixel sized filters. This Bayer Matrix is really the only difference between a monochrome and a OSC camera using the same CMOS/CCD chip. Each pixel has a single color filter overlaid on it. Generally in a block of 4 pixels you’ll generally have 1 blue, 1 red and 2 green. So you take an image and each of those pixels captures light through a single filter. The output is an image that has intensity data for each of those pixels, but no actual color to it (as the sensor is monochrome). However there actually is color information in the image as each pixel has a color filter in front of it.

Debayering is the process of matching the pixel with the correct color filter, then combining near by neighboring pixels to create a RGB image.

Thanks,
Jared


www.mainsequencesoftware.com