Struggling to move FITS file image center to specific coordinates?

Question

I have been tasked with aligning over 200 images of the sun.

I have made a template of a circle using the sun's disk position from one image. This template has a central (x,y) coordinate and a radius.

From there, I found the centre of my next image using a threshold of 1e4 (value of the pixels on the sun's disk, as opposed to 1e3 around). The code for that process is here:

# Get the indices of pixels that are above threshold
y_indices, x_indices = np.where(data >= 1e4)

# Calculate the centroid
centroid_y = np.mean(y_indices)
centroid_x = np.mean(x_indices)

Where data is the data from my FITS file.

I would like to align my FITS image to the template image by taking the centroid coordinates and moving the image so that they align with the coordinates for the template circle. For reference, here is an image where the centroid is displayed (red) along with the template centre coordinates (blue):

Image of the sun with two points: Red is the centroid, while blue is where I would like to align the centroid to.

I don't mind the image cropping - if anything, I will be cropping the images later anyway. I was looking into using pillow but I don't want to convert my files to PNGs as I will be performing analysis on them later and need the FITS file format. OpenCV doesn't seem to be working for me either - I'm new to code, so haven't been able to find what I need.

Thanks in advance.

Answer 1

I'm not really sure if you are asking for a library that can read and write FITS-format images, or how to calculate a centroid, or re-centre an image or how to crop.

I'll just point out that ImageMagick can read and write FITS images. You can see this if you run:

magick identify -list format | grep -i FITS

I have never worked with FITS images, so I would suggest you try this simple command to crop an image in half and see if the output file contains all you need before investing too much effort:

magick INPUT.FITS -crop 50%x RESULT.FITS

If that works how you expect, you can use wand which are Python bindings for ImageMagick and will allow you to do all the processing you want.

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I believe libvips can also read and write FITS images, though I have not tried.

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Note that if either wand or vips can read and write FITS images to your satisfaction, both can readily convert to and from Numpy arrays, so you can read/write with either but process with Numpy or OpenCV which works with Numpy arrays of pixels by default anyway.