Help overlaying images in Gimp

[dfc05]

I know nothing about image editing. Sorry if this is a stupid question...

How do you overlay two images in Gimp? I have two images, same dimensions, that I want to overlay so I can see both at the same time. It's basically an image of a crystal that's been translated downward, and I need to draw a line to show what direction it moved (technically I could just calculate this from the location of the corners, but I'd like an image actually showing this visually). Schematic of what I want to end up with after overlaying images 1 & 2:

I can post original images if that would help. The background is an irregular speckled gray, and the crystal is a darker gray. I thought that by opening one image, and the other as a layer, and by changing the layer opacity, I might be able to see the crystal in both simultaneously. But instead it just abruptly switches from one being visible to the other being visible. How do I get both to show up?

 

[Vegeta897]

Um, lowering the opacity on the top layer should give you what you're looking for.

Post the source images plox.

 

[dfc05]

When I lower opacity on the top layer, only the top layer is visible for opacities >50%, and only the bottom layer is visible for opacity <=50%.

I'm looking at the manual but it's talking about the "alpha channel" and I have no idea what that means .

 

[Vegeta897]

Oh, you have to add alpha channels to the layers. Right click them.

You are using that opacity slider, right?

Once you set your opacity for the top layer, right click it and click Merge Down. This will merge the layers, leaving you with one 100% opacity layer showing the result you want.

 

[dfc05]

Images uploaded here:
http://img109.imageshack.us/gal.php?g=mo1q.png

I'll need to keep the translation lines drawn on the 2nd image, then overlay that dot pattern over it and move the dots over so they're on top of the crystal.

I'll try putting the alpha layer stuff on. I think I checked alpha layer on the top one, and then I tried some crap with masks, and now I just have a big mess.

 

[Vegeta897]

I don't understand what you're trying to do with the dots image, but I'm having no problem changing layer opacity even without adding an alpha channel to the layers.

 

[dfc05]

Hmm, I must be really dumb or something. Here's exactly what I'm doing:

(1) Open Mo_1.tif (it comes up as the Background image)
(2) Open as layers... select Mo_2.tif
(3) With the top layer selected, I move the opacity slidebar.

If I try Merge Down after this, they merge but I still only see one crystal.

(Oddly, I'm getting a weird deja vu like I've tried this years ago and had the same problem.)

By the way, thanks so much for your help!

 

[Vegeta897]

What version of Gimp?

I just drag the first image onto the stage and it opens the image. Then I drag the other image into the layers window and it adds it as a layer. Then I make sure the top layer is selected, and drag the opacity slider.

If this isn't working for you, something about your Gimp must be different.

 

[dfc05]

It's version 2.6.8. I literally just downloaded and installed it an hour ago.

 

[Vegeta897]

That's really weird, bro.

Maybe it's worth mentioning that the images I downloaded from that album are PNGs, not TIF? I don't see why that would make a difference, though.

 

[dfc05]

Ah, imageshack converted and shrunk them. So I downloaded the png's and it's working now. This makes no sense to me, but whatever. Hopefully I can get the giant-sized images working too.

Thanks again!

 

[AtomicSpark]

You all have impressed me with your usage of Open Source software.

 

[dfc05]

I don't have Photoshop, and MSPaint can't overlay images, so Gimp was the only choice here .

Upon further experimentation, if I save the original .tif files as .png and try to work with those, it doesn't work. I'm not sure if it has something to do with the file being really big (they're 7 MB images). Kinda frustrating, but at least I don't need to count pixels on these (like I had to do with 9 other images) so it doesn't matter that much if I send it through whatever magic Imageshack is doing.

 

[VirusType2]

I'm pretty sure TIFF supports higher color anti-aliased edges for transparencies than PNG.

Wikipedia has a lot of information on image formats.

 

[PvtRyan]

So is the Gimp actually usable these days? I remember using it and was unable to find a tool to draw a rectangle. Eventually, I managed to draw one by making a selection and filling that with a color. Wtf.

 

[VirusType2]

I don't have Photoshop, and MSPaint can't overlay images, so Gimp was the only choice here .

Another good free one is Paint.NET. You may find it easier to use than GIMP. I found that Paint.NET was able to work on a particular TIFF image that Photoshop would not load for some reason.

On XP only, you'll need to have NET framework installed (from Microsoft) before you can install Paint.NET.