Aligning two images

Ray Perry

I have two datasets of M31, one set taken in September 2020 and the other in September 2021. 

2020 set of 59 x 120s lights, 21 x flats, 20 darks, 50 bias; 2021 set of 51 x 120s lights, 23 x flats 20 x darks, 50 bias.

I want to process both sets of data and then register them for use in the Normalise Scale Gradient Script and then on to an integrated masterfile.

My problem is that in one set of data the Andromeda Galaxy is about horizontal, but in the other set it is about 70 degrees from horizontal.

I have calibrated each set of images using WBPP 2.2 and NSGScript successfully and have 2 integrated images but you can’t register and integrate two images.

I have tried loading both sets of registered NSG files in Image Integration but I end up with an image of two overlapping Andromedas at the different angles.

Any help would be appreciated.

BlockHead

HI Ray,

I am not certain I understand.

You would want to calibrate (and debayer) the images from each set either all at once (or separately). Then you pick at single reference frame from one of the sets (say from the 2021 set) and align *all* images to it.

Then you take these registered frames (all 110 of them) into NSG (I am assuming this is an OSC camera) and let it do its thing. Finally you will be able to integrate and end up with a single image.

Just in case you ask... when you align the sets and choose the 2021 as the reference- the 2020 data will be aligned... but there will be black areas where the two images do not overlap. That is OK. The cool thing about NSG...is that it is very good at matching the gradient...and you should not end up with a terrible result in these areas.

-the Blockhead

Ray Perry

Hi

Thanks very much for the reply. I followed your instructions and ended up with a stacked master of 53 files. The other 57 all failed to star align - less than the required amount of stars.

When I star aligned each sessionj with its own Ref file, they all registered OK, but I understand that they all have to register with the same file.

Are there any settings I can tweak? I tried upping the Ransac tolerance from but this only added another five files at the maximum setting.

BlockHead

First, you don't want to stack do you? You want to generate just the registered files. You will need NSG to take care of the differences between images. For alignment between images that have different distortions- likely you need to use the Thin Plate algorithm in StarAlignment. I have not seen your data so I cannot know the difference in quality. Assuming things are the same with exception to the rotation of the images, things will work out. If you acquired the data using two different systems- alignment might require some small tweaks to get it to work well.

-the Blockhead

BlockHead

Make available 5 of your frames in each set- including the frame you chose as the reference and 5 of the frames of one set that did not align. I

-the BLockhead

Ray Perry

Thank you for your time. I started again from scratch. After Blinking both sets of registered images followed by NSG Script, I ended up with a Masterlight of 65 images which I will now process whilst going through the Fundamentals videos.

Ray Perry

What have I learnt from this? Always check the camera orientation on your target :)