Hopefully simple question

[spokeshave]

I just came across ImageMagick as I was looking for a simple way to convert FITS files to something more readable by other software like TIFF of JPEG. I do astrophotography and my color camera produces monochrome (undebayered) FITS files. I want to be able to debayer those files and then convert to either TIFF of JPEG. I can do that from the command line but I only get a grayscale image. I tried the -interpolate option and still got grayscale. Can someone please tell me how to make this conversion work? Many thinks in advance.

Incredible software, by the way. I'm astonished that I have not seen it before now.

Tim

[snibgo]

IM doesn't contain code for de-bayering. I show some methods using IM on my page http://im.snibgo.com/demosaic.htm

[spokeshave]

Ah. Thanks. I was hoping for one-stop shopping with ImageMagick. I am familiar with dcraw and use it to demosaic raw files from my DLSR. However dcraw cannot decode FITS files. Hence my dilemma. Is there a way to use ImageMagick to convert the FITS to something that dcraw can then decode?

Thanks.

Tim

[snibgo]

Can you put up an example FITS file? You can upload to somewhere like dropbox.com and paste the URL here.

[PandoraBox]

@snibgo

Ironically I had this in my bookmarks might be able to help out on this case.

http://fits.gsfc.nasa.gov/fits_samples.html

has some sample images they read like text so I'm assuming conversion might not be that bad to do... as for actual converters this site also has some.

PandoraBox

[snibgo]

Thanks for the link. I can't see any mention of Bayer arrays. The first three aren't Bayer. On the contrary, some mention "the 4 individual CCD chips", which isn't Bayer. IM Q32 HDRI can read these files, and make decent images from them. It reports that the third file, "HST FOC", is grayscale 32-bit/channel, with the maximum value of 2.08e-8 (on a scale of 0 to 1). With "-auto-level" it becomes visible.

When an image is made from three individual CCD chips, assuming they line up exactly and they record red, green and blue, a colour image can be made with "-combine". Very easy.

Digital cameras often have only one CCD chip, where each receptor has a colour filter so it captures only red or green or blue. This creates a gray (one channel) mosaic image that looks like a chequer-board when we zoom in. Each pixel represents only one channel. Converting these to colour is much more difficult. By de-Bayering (de-mosaicing), we interpolate the missing two-thirds of the data.

[spokeshave]

Can you put up an example FITS file? You can upload to somewhere like dropbox.com and paste the URL here.

Sure. Here's one:

https://www.dropbox.com/s/u1m1tgs0nhfdy ... 4.fit?dl=0

Thanks.

Tim

[snibgo]

Code: Select all

convert "Bubble Nebula_480sec_1x1__frame14.fit" b.png

set sCROP=-crop 40x80+775+1561

%IM%convert b.png %sCROP% -scale 400%% b_sc.png

Yes, that looks like Bayer. Enlarging one of the white blobs, I can see the typical mosaic pattern.

Assuming the pattern is RGGB, and the colour multipliers are all 1.0, we can use my demos.bat script to de-Bayer it:

Code: Select all

call %PICTBAT%demos b.png
%IM%convert b_dm.png %sCROP% -scale 400%% b_dm_sc.png

The result seems plausible.

The colour multipliers probably should not all be 1.0. Ordinary camera files normally contain this metadata, but your FITS file doesn't.

[spokeshave]

Yes, the color matrix is RGGB. For one-shot-color astronomical cameras, all color balancing is done in post-processing, so there is no color info in the header.

It looks like your batch file will work well. Thanks for the help.

Tim