Legacy ImageMagick Discussions Archive

Hello,

I have a bunch of images taken by our machine behind a green screen so ideally i need to be able to batch process them with IM.
I tried to use everything I could find on the web and this forum. Reading IM samples but couldn't reach a satisfying solution.

I would like to substitute the green screen by an image background.

Here are 3 images:

https://www.dropbox.com/s/vdmap3vql9gv2 ... 1.jpg?dl=0
https://www.dropbox.com/s/dq9lyluh72s55 ... 2.jpg?dl=0
https://www.dropbox.com/s/3364zoye669i7 ... 3.jpg?dl=0

Here is a picture of the green screen alone:
https://www.dropbox.com/s/l92h7ugnrc4h1 ... n.png?dl=0

Here is a picture of the background image as reference:

https://www.dropbox.com/s/njrisedxauqqb ... d.jpg?dl=0

Thanks in advance,
Laurent

To do background subtraction correctly, you need to avoid using JPEG images and have two background colors. See https://imagemagick.org/Usage/masking/#two_background.

With one color, you also need to have the background and image taken from the same perspective and lighting and no JPEG images to have the best chance. Your images are not perfectly aligned nor taken with the same lighting or the wrinkles give different shading from the lights. You should have a perfectly flat background. Thus my attempts to either do either a fuzzy change of color or background subtraction fail due to noisy results or different illumination.

Here are 3 increasingly better approaches. But they each have flaws.

Basically, I extract the HUE channel of the image and replace the green hue with black and the rest with white using a fuzzy color replacement to make a mask image. Then I do a 3 image composite where the third image is the mask and the first is the background and the second is the image. I do not use the image of the green screen, since it does not match well in color to the background green in the image due to lighting differences. The main issue here is that the screen is not evenly illuminated and the image is JPG with lossy compression, which cause blocky artifacts, which show in the mask image and the result.

Background:


Image:









Here are the hue and tmp files to show the progress of making the mask image

hue:



tmp1:



tmp2:



tmp3:

It's really close to the result I was getting. So I tried with PhotoShop and used the color range as well as the hue filter as explained here: https://lensvid.com/post-processing/how ... photoshop/

Would it be possible to get the equivalent in IM of the color range? If we could add several level of colors like the + in Photoshop and then save it as a png? That's what I am getting with an action in Photoshop and merging the background in IM.

https://www.dropbox.com/s/t1j9a9oyzb1y4 ... 2.jpg?dl=0

Here is the png delivered by PhotoShop:

https://www.dropbox.com/s/6ph63vi5dix1m ... 1.png?dl=0

I will review that document and see. But Photoshop is interactive and Imagemagick is not. So there is no feed back that lets you see what colors to add.

Can you send your photoshop files and the action your created. It would help me understand what you are doing. You can send offline via PM on this forum or to my private email as shown on my web site at my link below.