I have been trying to learn the basics of Blender and I have a basic understanding of keying. But here is my problem. I only have a blue screen and I am trying to utilize it. The problem is I have blue object which is interfering the keying process. I would like to know if it is really possible to still use the same blue screen and do the keying for the below image.

actual footage

This is what happens when I try to apply the knowledge I have.


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    $\begingroup$ I don't think there is enough contrast anyway. You have the same blue values inside your object. You can try to use the LumaKey, but you'll have to mask out the interior manually. $\endgroup$ – Carlo Dec 25 '20 at 17:57

Keying with a color background that is similar to the objects in the foreground is not a good idea...

Also, the background is not an uniform color, since the fabric has folds and wrinkles, so you will have to key out a large amount of different tones of blue, which will force you to use very aggressive settings for the key, which in turn will result in too much of the image being affected and degraded.

But since you voluntarily put your self on a bind and a challenge, you will have to work extra. KEY the background like you would normally, then you will need to create masks for the blue pail, and use those as core matte.

enter image description here

But you will notice that the key node has also taken away a lot of the blue component from the image, so the output has become useless.

You will then need to use the original image and associate the matte created by the key node and use it directly on the image with a set alpha node and an alpha convert node...

enter image description here

Then you will need additional masks to use as garbage matte to get rid of the dark areas (the folds on the fabric) to have a clean matte.

enter image description here

Then you'll realize that you need to bring back the shadow from the pail on the fabric... Getting the shadow information (and subtle gradations like reflections or transparency) would have been very easy to do with a proper flat background, but now you need to re-invent that portion of the image.

Then you'll realize that one of the other blue objects is also missing, so you need more masks...

This is way too much work for something that should have been very simple (and mostly automatic), extra work that could and should be avoided with proper preparation...

Now that you've seen the extra effort that it takes to do this, change the fabric to a color that is not present on the scene, stretch it so that it has no folds, and make a new picture and key it in a simpler and proper way... Key out that color so that you have a clear edge on the objects, enough information on the shadows and reflections and so on.

Even a black fabric would be easier to key (using a luminance key) than what what you have right now.

  • $\begingroup$ Thank you for your detailed answer. I guess its time to get a different color mat and save time. $\endgroup$ – Andro Selva Dec 26 '20 at 7:50
  • $\begingroup$ @susu I'm trying to learn more about the compositor.. I couldn't help noticing that Hue alone made a pretty good discriminator for a core matte, here: (imgur.com/a/KMKpIjn).. but struggled to get it to work with single channel or one of the other key options. Do you have any clues how you would get that to work, a 'proper' way, without assembling it by hand, getting decent anti-aliasing, etc? ... Maybe this is another question... $\endgroup$ – Robin Betts Dec 26 '20 at 11:32
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    $\begingroup$ @RobinBetts there are indeed more than one ways to skin this cat. I was just pointing out the core problem. Blue is the noisiest noisiest channel for anything that comes out of a camera, so it only used in cases where green cannot be used, green being the channel with the most information. The keyer node tries to simplify, for novice users, an operation that requires a bit more of a careful approach. $\endgroup$ – susu Dec 26 '20 at 12:22
  • $\begingroup$ @RobinBetts Ideally you want to make a difference key, with the background using a clean plate, that has all of the pixels that would be missing if the objects were not there. Use inpaint, along with the matte you are creating, to generate such clean plate, and then a difference keyer should work fine. To have clean or smoother borders you might want to generate some feathering. I'm curious on your answer. $\endgroup$ – susu Dec 26 '20 at 12:28

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