How to combine panels with different image scales.

[mackiedlm]

I have 3 panels for a mosaic. All taken with the same camera but 2 panels (top and middle) at 510mm FL and 1 panel (bottom) at 275mm FL. I will build the mosaic in Pixinsight using Photometric Mosaic Script  and can do that without problem.

Unfortunately I dont really understand the whole resolution/upsampling/downsampling business well enough so am struggling to decide which panel to use as the reference image such that I dont lose any detail or resolution in the process.

Any help would be appreciated

[vlaiv]

If you choose panel shot at 510mm FL as a reference, then you run a risk of part of image being visibly more blurred than the rest of it - 275mm FL panel will not look as nice as others when enlarged to their size.

If you choose 275mm FL - then whole image will be "smaller" in size - objects in it will be of a smaller size when viewed at 100% zoom level. It will look the same when you fit it to screen - then either of them will be the size of screen so objects in each image will look the same size (by each image I mean one registered to 510mm FL panel and one registered to 275mm panel).

Although I know what I meant, I'm not sure I was particularly understandable, so I'll reiterate in bullet points.

Registering to 275mm panel:

- smaller total size of image in pixels

- smaller objects (compared to other option) when viewed at 100% zoom, but equal size when viewed "fit to screen"

- whole image will look equally sharp when viewed at 100% zoom

Registering to 510mm FL panel:

- larger total size of image in pixels

- larger objects at 100% zoom level

- risk of part of image looking visibly more blurred then the rest of it (panel that was shot at 275mm will look more blurred then the rest).

[mackiedlm]

31 minutes ago, vlaiv said:

If you choose panel shot at 510mm FL as a reference, then you run a risk of part of image being visibly more blurred than the rest of it - 275mm FL panel will not look as nice as others when enlarged to their size.

If you choose 275mm FL - then whole image will be "smaller" in size - objects in it will be of a smaller size when viewed at 100% zoom level. It will look the same when you fit it to screen - then either of them will be the size of screen so objects in each image will look the same size (by each image I mean one registered to 510mm FL panel and one registered to 275mm panel).

Although I know what I meant, I'm not sure I was particularly understandable, so I'll reiterate in bullet points.

Registering to 275mm panel:

- smaller total size of image in pixels

- smaller objects (compared to other option) when viewed at 100% zoom, but equal size when viewed "fit to screen"

- whole image will look equally sharp when viewed at 100% zoom

Registering to 510mm FL panel:

- larger total size of image in pixels

- larger objects at 100% zoom level

- risk of part of image looking visibly more blurred then the rest of it (panel that was shot at 275mm will look more blurred then the rest).

Thanks Vlaiv - thats exactly what I needed!

 

As a follow up question, what happens the second case (registering to the 510 panel) in the overlap area. I the image I am working on there is an overlap area which holds some quite small detail. Will the 275mm panel significantly degrade this area of detail? I have already processed the image this way (registered to the middle 510mm panel) and i am relatively happy with it. I think the lower panel (as you indicated) does look more blurred but as there as not much in that panel I was willing to live with, I'll post that image up in the DSO page.

 

Thanks again

[vlaiv]

1 minute ago, mackiedlm said:

Will the 275mm panel significantly degrade this area of detail?

Not significantly.

In overlap area there is usually "feathering" like effect - or linear transition between the two panels. Where overlap starts 100% - 0% mix is used than that gradually goes to 50%-50% at the middle and then to 0%-100% on the other side of the joint or transition area.

In that 50%-50% - data will be "half as blurred" as in 275% panel, or somewhere in between the two.

[mackiedlm]

thanks @Vlaiv, I've just posted it up so you can take a look if you are interested. The overlap does cover the pillars area in NGC7822 and i dont think they hare significantly degarded - as you have explained/