Having major superimpose problems!!

[samweisberg]

Hi,

Hoping someone can help me with this problem! I am new to Gimp 2.10.30 and I'm trying to superimpose several black and white photos over a bigger one. I followed all the instructions, used "color to alpha" mode on the smaller/superimposed photo, erased all the parts I didn't want included in the photo, opened up both the background photo and superimposed photo as layers...and still it looks like the photo below. As you can see, the superimposed photo is barely visible (all you see are the guy's legs!), and I've tried all sorts of lighting/shadow/opacity fiddling to make it work, to no avail. Can someone please help me fix this?? Thanks!

[Ofnuts]

Possibly because when you used color-to-alpha everything became partly transparent. Color-to-alpha is usually not the right way to extract things from photos. If you extract was on a solid background you can extract it again like this:

• Use the wand selector to select the background
  
• Select ➤ Grow by two pixels so that the selection covers the edge pixels
  
• Use Color-to-alpha. It will only apply to the selection and the core of the subject, being un-selected, will remain fully opaque.
  

[rich2005]

Quote:...I followed all the instructions, used "color to alpha" mode on the smaller/superimposed photo, erased all the parts I didn't want included in the photo, opened up both the background photo and superimposed photo as layers..

Who gave those instructions ? It is indeed one way of adding to a base image.

Your problem is the colour-to-alpha (c2a) by default removes all the selected background colour, often white but can be any solid colour. Your image will show transparency (the checker pattern) through the foreground.

With Gimp 2.10 c2a there is an additional slider, Opacity Threshold, adjust that to improve the image.
That can have consequences, a unwanted border of the old BG colour. Remove that before adding to the background image. Layer > Transparency > Alpha-to-selection then Selection > Shrink by a couple of pixels Now copy > Paste into the main image.

An animation of that: https://i.imgur.com/eaM0zbc.mp4

No doubt someone will come along with a plugin reference that does all that automatically but it is worth knowing what is going on.

Other ways, and probably what I would use. The figure added as a new layer and a layer mask to remove the BG.

[PixLab]

(04-25-2022, 08:07 AM)rich2005 Wrote:

Quote:...I followed all the instructions, used "color to alpha" mode on the smaller/superimposed photo, erased all the parts I didn't want included in the photo, opened up both the background photo and superimposed photo as layers..

Who gave those instructions ?  It is indeed one way of adding to a base image.

Indeed who told you that? where are those instructions?
Please give us the 2 pictures to merge.
There are many-many ways like they said above, channels/curves/threshold and so might be the way as well, but one way which works with 2 pictures might/will not work for 2 others different pictures.

[rich2005]

Following on, more information really needed. However, reading between the lines maybe the background(s) are complicated and a simple fuzzy select or c2a is not effective.

Back to basics, Using the Foreground Select tool to get a selection and a layer mask for a tidy up.

Example: duration 4 minutes https://youtu.be/m9_Mz2VbSjA

Yes, editing can be tedious but often necessary.

[sallyanne]

You could also try to change the opacity of the smaller image, if you want to see the background through it.
Actually depends if you want a 'ghost' like look or not. Try all the layer modes with the small picture/s selected and see which give you the desired effect.