My First Mosaic – and how I did it.

Inspired by Geoff’s results I tried using the automerge in photoshop on my pictures of the Heart and Soul Nebulas. Oddly it only matched them if I selected the Soul first! Unfortunately it doesn’t rotate the images and my two sessions were at quite different angles for some reason.

I have combined images in photoshop before, but only on top of each other, never as a mosaic, but i decided to follow a similar path:

First I doubled the canvas size for the Soul image an imported the Heart as a layer on top.

I set opacity (opposite of transparency) of the heart image to 50%, and guided by stellarium to find the rough alignment it was easy to find a small asterism on both images. Zoomed in, I overlapped one of the stars in the asterism as accurately as I could. Circles of smeared stars around this point gave an idea of how much rotation would be needed.

using the select tool I then moved the centre marker of the Heart image over the centre of the aligned star and went to the edit menu to select ‘free transform’. This opens boxes where you can alter things like horizontal and vertical size and skew the image – not needed for images at the same scale. Instead I just used the ‘rotate’ box – this lest you enter angles in increments of +/- 0.05 degrees. This may sound a quite big step, but actually I’ve found it is small enough to align stars across a whole image. It’s easiest to step in whole degrees, then tenths of a degree and finish by using 0.05 degree to get the best possible result. It’s very obvious when you are aligned as the overlapping area suddenly looks much sharper.

I then changed to the magnifying glass tool – this brings up a box asking you if you want to apply the transformation – click yes if you are happy!

I then restored the Heart image to 100% opacity. It was clear it was less contrasty and a bit paler background. I used the ‘levels’ dialogue to alter gamma and black point until it looked a closer match to the Soul – you could also do this with curves. the whole thing might have been better if I had originally process the two images the same way.

Once they matched there was still an area of overlap with poor quality in the corner of the Heart image. I used the lasso tool with a feathered edge to remove most of this corner. A small patch still appeared too pale, so I lassoed it and changed its levels to match better.

This is the result, not perfect but not bad either:

Heart and Soul
Heart and Soul Nebulas

Decomposing images in GIMP2

Tonight, I took my first image of the Moon with my QHY10 camera/Equinox 80mm telescope.

The image should colour dispersion. I do have a dispersion corrector but it is 1.25 inch fitting and the QHY10 camera is definitely 2 inch fitting.

I found that this problem can be addressed using GIMP2 software – in this software there is a function called decomposition – this splits a colour image into separate individual RGB images.

I have described the process I followed in GIMP2 to decompose images below.


Original image in GIM2 showing colour dispersion:

Selecting decompose in GIMP2:

Selecting RGB in decompose:

Decompose in GIMP2 results in 3 separate layers for each colour – each image is presented greyscale & can be saved:

Jupiter 20-21 June 2019

I did 33 runs on Jupiter last night. The Red spot was well paced, as was Io transiting the planet, but although it’s shadow is clear there is only a hint of the moon.

My ADC made a huge difference.This was with the ZWO ASI120MC, x3 barlow and 150PL.

For this session, wavelets worked better than deconvolution giving a smoother result.




Thanks to Ed for bringing VideoPad to our attention at begginners’ RAG group. His super demonstration showed how useful it was. It was clear that this is a good replacement for the much lamented MovieMaker. I went home and tried out the free version. As ever with video software it is a bit tricky, especially when trying to make changes to something you have already done. I went back and inserted a title and then had to shuffle the clips to fill in the gap. Still I was delighted to be able to crop the clips and make a compilation.

I’m afraid my first attempt is not astronomical. Still you might want to see how it turned out. It is at – . I now know that using the typewriter effect for the title is not good, as it makes for a blank preview image. To hook people in I would have been better with no title at all. Still it did what I wanted to.

So far I’ve not been nagged about upgrading to the paid version, but I am so pleased with it that I think I will do that eventually. I’m looking forward to trying out other features.

Thanks again to Ed for suggesting this software. I look forward to reading anybody else’s comments and tips when they have had a chance to try it out. I’ll let you know when I’ve done something a little more RAG orientated 🙂