grid pattern on image

[Duke2k]

Hi all

I'm relatively new to imaging and I am using a ZWO ASI224mc with a cpc 9.25.

I have had a lot of good images of planets using Firecapture, AS2, Registax6.

The other day I attempted to image the eskimo nebula using 4 second exposures as my scope is alt az mounted and I don't have a wedge. However there appears to be a grid pattern on my image that isn't related to the pixels.

I only took 15 frames and no darks or flats so do I simply need more images with the darks and flats to remove this?

A friend of mine also has the same camera and is using it on a ODK16 and he is getting the same pattern on a single frame from a sequence. This pattern doesn't appear on the laptop screen during capture.

I have attached the stacked image of the eskimo and a moon image from his setup. Any help on what this is why it is happening and how to prevent it would be great.

The final image is a stack of 500 lights and 170 darks but the pattern is worse.

 

Thanks

 

[vlaiv]

Asi224mc is color camera, and your shots look black and white. How do you process your images?

For color camera you have to treat data as bayer matrix and do debayering, don't treat them as b&w - if you do you will get grid pattern artifacts like that.

[Uranium235]

Yep, the images need debayering. Run the subs through DSS when stacking and that will do the job for you.

[ollypenrice]

Although software should do this in the correct order anyway, you must debayer before combining the images into a stack.

Olly

[Duke2k]

Thanks Guys that's a great help. The eskimo frames were saved as fits files but I cant find how to debayer them in DSS. Under the RAW/FITS DDP settings I have ticked the top box and chosen generic RGGB and bilinear but it still processes them as grey and not colour.

Is there a better way to do this?

What file type is the best is it RAW?

Is DSS the best free stacking program for deep sky images?

Thanks

 

[vlaiv]

Fits is OK format for that (I do all of my recording in fits files).

Yes, in DSS in RAW/FITS DDP settings on second tab - one for fits make sure it's checked before you add light frames - when you add light frames it should mark them as color (not mono) - then it will debayer. DSS usually behaves strange when I load light / dark / bias frames and then switch this option - it complains about size or something, so I have to mark this option before loading files.

Can't give an answer to the question if DSS is the best - I decided not to use it anymore and do all my processing in ImageJ - but this is due to memory issues with DSS and the fact it uses 16bit precision for calibration (not good when you have many frames). So I consider ImageJ to be better suited for my needs - but mind you, it is not going to work out of the box, many things need to be done manually, and I even wrote couple of plugins to do what I need.

[Duke2k]

Thanks I have just tried that and they are still listed as grey files. screengrabs added.

[vlaiv]

That is strange.

Maybe try just one more thing - not sure if it will help, but just in case.

Repeat the process, but this time delete all .txt files from previous registration before you start DSS and add light frames, and also any auto save files that may exist in folder with lights.

I suspect that color / grayscale might be written along with other params in .txt files and is read in when you add your light files (score, FWHM and Sky background are all there from previous registration).

[Duke2k]

Ok I have just done that so now there are only the fits files, but its still the same issue. I notice it mentions 16bit fits images but I'm not sure if mine were 16 or 8 bit or are they all 16?

I will try again later if the sky remains clear and go from there. Thanks for your help.

[michael8554]

If you have any doubts about the Bayer setting, take some daytime shots of scenery and experiment with the setting until the colour looks right.

Michael

[Duke2k]

Thanks for your help guys, It was indeed a bayer issue and after following your advice it is now ok.

[Pat Warborg]

On 2/13/2017 at 01:01, Duke2k said:

Thanks for your help guys, It was indeed a bayer issue and after following your advice it is now ok.

Wait a second...! What exactly did you do to solve your problem? I'm in the same situation right now. I took about 100 4s images of M57 with SharpCap. They are saved as 8 bit raw fits. No matter what I try, they always show up as 8 bit greyscale in DSS (and result in a greyscale image after stacking). I did all that was mentioned above (deleted all previously created DSS files, first applied the fits settings in DSS, then loaded the lights). They are still listed as greyscale 8 bit. I'm wondering if DSS can handle these 8 bit files in the first place? In the settings dialog it mentions 16 bit raw fits only...? Btw, the fits header of the files say that the bayer pattern is GBRG. I suppose that's the one to choose in the DSS settings (in contrast to what you showed in your screen shot, Duke)?

Any help would be greatly appreciated!

CS, Pat