PixInsight Forum (historical)

PixInsight => General => Topic started by: MineralMike on 2019 December 09 10:35:26

Title: Can't get a mosaic with GradientMergeMosaic
Post by: MineralMike on 2019 December 09 10:35:26

I'm trying to make a two-panel mosaic of the Rosette, and can't get GradientMergeMosaic to do the job. Here's what I've done:

• Read Keller's book on the topic
• Viewed Harry's video on the topic
• Star-aligned and saved both panels per Keller's book
• Cropped the panels to exactly the same size
• Opened GradientMergeMosaic and added the two images, then clicked Apply Global

The resulting mosaic has the panels overlaid one on top of the other. Please see the attached screen shot.

What am I missing? How do I make a mosaic that connects, not overlays, the panels?

BTW, I made a prelimiinary two-panel mosaic in StarAlign, but the overlap was imperfect, so I wanted to use GradientMergeMosaic for a better result.So i know the images can be joined. How?

Thanks for all advice.

--- mike

Title: Re: Can't get a mosaic with GradientMergeMosaic
Post by: pfile on 2019 December 09 11:19:28

GMM requires the input images to be the same size as the final image. so i think the trouble is the step where you have cropped the images.

in your case one image should be black on the left and contain the nebula on the right, and the other should be black on the right and contain the nebula on the right. both images should have the same dimensions.

you shouldn't have to do any cropping; whenever you are making a mosaic you either need a reference frame that spans the entire mosaic, or you need to use MosaicByCoordinates which will generate input files in the fashion that GMM expects.

rob

Title: Re: Can't get a mosaic with GradientMergeMosaic
Post by: MineralMike on 2019 December 09 11:38:18

OH! I didn't know that.

Thank you very much for your prompt and informative reply. I will try making both panels the size of the final image.

--- Mike

Title: Re: Can't get a mosaic with GradientMergeMosaic
Post by: MineralMike on 2019 December 10 10:26:48

Follow-up: I went through the steps to create two final-size, half-black, star-aligned panels, then I joined those with GradientMergeMosaic. The result turned out well, and I posted it as a preliminary image in the Files section of my website: http://astronomy.mdodd.com/files/Rosette_full_mosaic.jpg (http://astronomy.mdodd.com/files/Rosette_full_mosaic.jpg)

This is Ha only. I'll add full-color subs when the Moon goes away.

Thanks again for the information. I now have the workflow memorized and documented.  :laugh:

Mike
http://astronomy.mdodd.com

Title: Re: Can't get a mosaic with GradientMergeMosaic
Post by: pfile on 2019 December 10 13:41:19

looks good, looking forward to the RGB.

only thing i would say is that on the left the color is a little different so i wonder if there is a gradient in that half that didn't get removed?

rob

Title: Re: Can't get a mosaic with GradientMergeMosaic
Post by: MineralMike on 2019 December 10 17:05:20

I'll try again when I have the full-color subs to add. I might also reduce the number of Ha subs. Waiting for clear skies and a first-quarter moon....

--- Mike