OSC Camera Images Open as GrayScale

[SeattleStarGazer]

Images taken with my ASI294M PRO Cool in SGP open as grayscale and can't be converted to color in PI.  In the FITS header I can't find any info related. The top line says SIMPLE T file does not conform to FITS standard. What may be happening?

Thanks,

Wayne

[Niall Saunders]

Hi Wayne,

A 'raw' (un-modified) image taken by your OSC - as is (usually) the case with all high-end OSC imagers - will always be downloaded to your PC as a 'grey-scale' image. After all, that is what the image actually 'is'.

Once you have this grey-scale image, this is where programs like PixInsight come into force. They can be used to 'convert' the grey-scale images into colour images, using information supplied by what is known as the "Bayer Matrix" (sometimes also referred to as the 'CFA') for your imager, to look at each and every pixel in your image in order to determine the colour of light that 'must have been' incident on the Colour-Filter Array at that pixel (and also at neighbouring pixels as well, in most cases).

So, it is then your job to perform the required image acquisition steps prior to then using the likes of PI to 'calibrate' and 'intergate' your data to create a final image ready for post-processing (again, in the likes of PI). At some point during the pre-processing phase, you will perform the DeBayering step, where you will change from greyscale to colour.

However, it is not just a case of performing the DeBayering step - don't expect to see glorious colour at that point. In fact, it is highly likely that you won't be able to see any colour at all until you are well into the post-processing srages. Even then, the colours that you do see will probably not be the colours that you might be expecting. You still have more post-processing ahead of you!

Just remember, taking images of what are really incredibly, ridiculously, faint objects is just nothing like taking images in bright daylight.

If the task was easy, everybody would be doing it     

[SeattleStarGazer]

Thanks! I did some more exploring and tried the debater on some imag e and got error messages. I am away from my pc and don’t remember the exact messages, but it was like unrecognizable format?? Not sure if there are settings I need to make. It was in ASI RAW16 format.

[SeattleStarGazer]

S here's what happens. Debayer settings Auto with Demosaic method DNG. Turned off evaluate noise. Entered my list of files, PI crashed. Entered one file, get this message


*** Error: Unable to acquire CFA pattern information: Unavailable or invalid image properties.

[Niall Saunders]

I'm not a fan of 'auto' settings in general. And I am especially not a fan of trying to DeBayer in 'auto detect' mode (where PixInsight will attempt to determine your CFA based on an algorithmic approach).

I have always set out with the intention of determining the exact nature of my imager's CFA by an empirical approach as, inevitably, even the manufacturer's datasheet (for the sensor itself) will not tell you how the CFA was actually implemented by the designer of the imager as a whole, and that is before you consider how your selected image acquisition software then chooses to save the RAW image to disc.

Instead, I usually expose the imager (without OTA, it serves no purpose for this part of the investigation) to different shades of colour, either by reflecting white light off a sheet of coloured paper (one sheet each for Red, Green and Blue), or by passing light through different filters (again, one each for Rd, Gn and Bu). I keep a set of A4/Legal size sheets, printed on a professional quality printer in a safe, damp- and loght-proof container, so that I only have to have them printed once. I also keep a set of 1.25" RGB filters (ex Meade DSI Pro imager) as an alternative - although you can get coloured acetate sheet from several popular on-line sources, and these can do a very similar job.

I then load the RAW images into PI (three at a time, one each for Rd, Gn and Bu illumination) and zoom into the very top-left corner of each image - where PI normally defines its (0, 0) pixel position. (Obviously, the image data that you acquire has to be in a 1x1 un-binned mode). From knowledge of which image was exposed to which colour at the time of capture, I then determine the size and layout of the CFA.

Alternatively, as it is pretty unlikely that your imager has a CFA that has not already been taken into consideration by PI, you can DeBayer each RAW image, using each of the proposed CFA settings available within PI, and you can then see which setting returns the correct three image colours for all three RAW images.

Once you are happy with a result - take a note of it somewhere. It is important, and will not change unless you change imager, or (sometimes) unless you change image acquisition software.

Hope this helps.

[SeattleStarGazer]

Turns out it's RGGB, which does get me some relatively correct color. I suspect that it's the smoky haze in the air that's causing the muted brownish colors that seem to cover everything, it's just more of an impact than I expected

[Niall Saunders]

Hi Wayne,

Just keep persevering - your 'result' (where you believe that your CFA is RGGB) is certainly 'acceptable', so continue on that basis unless you then feel that things still aren't quite right.