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I am usually proficient in Photoshop but this one is really stumping me. I have two almost identical images and I need to separate the differences onto a new transparent layer for overlaying with other similar images. For example

Here is the original image

enter image description here

Here is the image with the small changes (red dots)

enter image description here

I need the red dots alone, on a new layer with a transparent background so I can overlay them with other maps. Any help?

  • Well, I cheated and selected (select -> color range) the color red, copied it to a new layer and threw on a 1px black stroke. Looked almost identical. However if someone could explain how to do it correctly for the future that would be awesome, thanks! – SuperMar1o Jul 3 '15 at 20:32
  • Honestly, that's how I would do (and have done) it. (I've had to pull the "traffic" data from google maps into a separate layer in the past). – Voxwoman Jul 3 '15 at 20:40
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It's not a perfect technique, some pixels will be destroyed, it will also destroy some anti-aliasing, and you'll also lose that small shadow around the dots. But it can be easier to isolate your dots this way and not drag some of the map background with the dots.

There's many ways to do this, including selecting the red color and copy/pasting them on a new layer.


Here is another technique that I would use for this (I personally don't like using the wand tool):

1) Set your color mode to CMYK

2) Open the channel window; delete everything in the Cyan and Yellow channel

3) On the magenta channel, open your "levels" and use the white color picker on the midtones until all the pixels from the names disappear.

Channel magenta Adobe Photoshop

An alternative: Boost the curve of the magenta instead, to make the lighter part white

curve magenta channel

4) Do the same with the black channel, but make the black around the circle to 100% using the black color picker too.

black channel

5) You will need to delete manually some stuff like the word "United State" and some cities, but it's quickly done with the rectangle selection tool. They should be only on your black channel at this point.

magenta and black channels together

6) Boost back the magenta color to red using hue/saturation, selective color or anything you prefer for this.

7) You'll end up with a white background. You can delete the white or use a multiply blending on your top layer.


Here is the final result with the layer with the dots using "multiply" but no shadow.

map without shadow and with multiply blending mode

Here is the final result with the transparent background and a drop shadow:

  • If you use a small drop shadow, it will smooth a bit the edges of your circles.
  • You can also add a 1pt black stroke; I used one at 75% transparency to simulate the anti-aliasing and not make the edges too dark.

map without background and drop shadow applied


Note: The screenshots for the "steps" are zoomed in; the quality looks a bit better at 100%.

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My aproach would be:

1) Copy one image and paste it as a new layer over the other image.

2) Set the Layer mode to Diference.

3) Flatten the image.

4) Invert the image (negative).

5) Clean it.

This technique can be used not only in this case but also with photos.

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