Comparing images
Feb 27, 2021 14:50:10 #
Every so often I want to compare two images. I use my normal viewer to bring up both images in separate windows and look from one to the other. Works fine if I'm only looking at the overall image, but if I want to get down into the detail, I have to expand the images to show the detail. That sometimes presents problems depending on what you are using to view the images. And if I want to get down into the pixel detail to look for differences it's hard looking from one image to the other to find subtle differences.
I found a way to do this in Photoshop. I can load the two images as layers in Photoshop. I can then go through the process to make an animated gif from the two images. (If the images are really different pictures rather than different versions of the same image it helps to have Photoshop align them first). When you get a couple frames set up for the animation you can run it in Photoshop. You don't have to actually save it as a gif file, although you can if you want to. When you run the animation Photoshop will display one image, then switch quickly to the other and back. You can control how fast it switches back and forth. I have my Photoshop set up to zoom in or out with the mouse wheel, so you can easily zoom in on a feature and look at it in detail.
In the early days of astronomy this process was done mechanically with different sky photos (negatives) to look for things in the sky that move. They called it a Blink Test. Today most of astronomy is digital so the blink test is done with software.
I suspect you can do this with other layer-enabled editing programs although I haven't done much experimentation. I did try GIMP and could get it to generate an animation but was unable to zoom in to look at details. There may be a way to do that but I haven[t found it.
The Photoshop process is described at https://www.uglyhedgehog.com/user-page?upnum=3016
PS: The process is not limited to two images. You can look at a sequence of images but too many might get confusing.
PPS: someone might want to write an Action to load into Photoshop to do this.
I found a way to do this in Photoshop. I can load the two images as layers in Photoshop. I can then go through the process to make an animated gif from the two images. (If the images are really different pictures rather than different versions of the same image it helps to have Photoshop align them first). When you get a couple frames set up for the animation you can run it in Photoshop. You don't have to actually save it as a gif file, although you can if you want to. When you run the animation Photoshop will display one image, then switch quickly to the other and back. You can control how fast it switches back and forth. I have my Photoshop set up to zoom in or out with the mouse wheel, so you can easily zoom in on a feature and look at it in detail.
In the early days of astronomy this process was done mechanically with different sky photos (negatives) to look for things in the sky that move. They called it a Blink Test. Today most of astronomy is digital so the blink test is done with software.
I suspect you can do this with other layer-enabled editing programs although I haven't done much experimentation. I did try GIMP and could get it to generate an animation but was unable to zoom in to look at details. There may be a way to do that but I haven[t found it.
The Photoshop process is described at https://www.uglyhedgehog.com/user-page?upnum=3016
PS: The process is not limited to two images. You can look at a sequence of images but too many might get confusing.
PPS: someone might want to write an Action to load into Photoshop to do this.
Feb 27, 2021 15:50:29 #
Many thanks for your time in preparing and sharing these tips. Great stuff!
I added a link to our Tutorials page:
https://www.uglyhedgehog.com/t-645056-1.html#11192295
.
I added a link to our Tutorials page:
https://www.uglyhedgehog.com/t-645056-1.html#11192295
.
Mar 2, 2021 13:57:45 #
Found an online comparison site. Drop two images on it and you get an image with a slider. Haven't seen a way to zoom in.
https://www.diffchecker.com/image-diff/
https://www.diffchecker.com/image-diff/
Mar 2, 2021 19:48:33 #
Mar 2, 2021 19:56:13 #
I found a couple things online, thanks. It’s not something I need at the moment. And my JavaScript is pretty rusty. I’m concentrating on Python right now.
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