Combining Images in GIMP

[Marky1973]

Hi All

I'm playing around with layers in GIMP as I had no idea how to use them two days ago, but am now fairly comfortable loading a couple of images, aligning them, adding a layer mask and using the paintbrush tool to allow one to come through to the other. The plan is to have a go with some long and some short images of Orion and combine the two final stacked images to get the nebula and the core.

I need to work on getting the two stacked images' "brightness" levels more similar as the ones I am playing with are a bit different and when using the paintbrush tool to bring the rear image "out" the blend isn't very subtle.

Am I working on the right principle here, or is there a better way to merge or blend in GIMP? I've tried using those controls, but they don't seem to change anything, so I suspect I need to so more work in that area.

If anyone has any favourite tutorials that they use and are willing to share that would be great.

Cheers!

[uhb1966]

You might want to Google for 'Gimp HDR tutorial'. You can mask the pictures more easily together...

[Marky1973]

Thanks again UHB, I'll have a look for that!

[dph1nm]

To average layers together you just set the opacity to 1/N where N is the layer number and use 'normal' blend mode. So layer 1 is 100%, layer 2 is 50%, layer 3 is 33% etc

NigelM

[Marky1973]

Hi Nigel - is that simply via the sliders above the images in the Layer window?

[dph1nm]

Yes.  Below (or above?) the blend mode menu at the top of the layers box there is a slider (and also a little box where you can type in the % number if you find the slide tricky to use as I do!). So just select each layer in turn and set the opacity, then use "merge visible layers" or "merge down".  If you set the opacity to something other than 1/N (in percent by the way, so 1/3 is 33.33%) then you give more or less weight to that particular layer. So you were trying to stack lots of subs of the same exposure time you would do 1/N, but if you were stacking stacks with different total exposures you could change the weighting so the longer stack got more.

NigelM