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Subject

I have a photogenic small dog and often use her for greeting cards and so on. It would be nice to choose different backgrounds according to the season etc.

Hardware

At the moment, my equipment is primitive, literally a Huawei P-Smart mobile phone. Max resolution [4:3] 13 MP. I'm considering something better, especially if it will do double duty as a webcam.

Software

I am quite skilled with editing in Microsoft Paint (don't laugh !!!) and have made some pretty good cards but finding the edges of a hairy dog isn't easy by hand.


It would make my pictures editing a lot easier if I could photo my dog and other subjects against a green-screen background and use better software to edit them into background scenes.

Question

Does the screen have to be green? Why? Wouldn't any neutral, even background such as blanket do? What is the science?

If I decide to dye a bed sheet, is there any special shade of green that I should use? If so, what is special about that shade?


Note

I live in a smallish flat and my dog is small so I don't need or want anything large in the way of a screen let alone a studio.

EDIT

I realise now that it would have been useful to post a picture. I cut around the edges of the blanket in Paint and then pasted onto a stock background.

enter image description here

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Greenscreen is technically a specific green (it registers on a display as being entirely 'green gun' nothing else - however most green screen software is pretty flexible on that, so in practice, anywhere close will do.

Bluescreen is an alternative, used predominantly in the movie industry, though I don't know why. they will use bluescreen to mask off an entire area behind buildings etc to map in landscape in CGI, but then will use green if they need to mask a character, for eg a missing arm etc.

As mentioned in comments & other answers it doesn't have to be green or blue, these are just far enough away from most other natural colours as to be easier to pick out by the software.

You can buy dedicated greenscreen in a non-woven paper-like form for a few $£€ on eBay, which is probably worth a look.

Your backdrop needs to be fully illuminated, separately from your subject.
With either green or blue there can be an issue with reflected light casting onto your subject. In an ideal world, your subject shouldn't be near enough the backdrop for this to be a major issue. In a living room with a small dog that's going to have to stand right on it, this is likely going to be a problem.

Good greenscreen software can eliminate this to quite a large extent, but the 'good stuff' isn't cheap. The likes of PhotoKey Pro though I expect newer AI-based structures will overtake this in the not too distant future. This is going to be a space to watch. A lot of the effort in this direction is being done on the moving image, with stills taking a bit of a back seat at the moment, but it will come in the not-too-distant future. The new Photoshop 2021 apparently has something along these lines, but I've not made the jump yet. I like to give them 6 months for things to settle down.

The only real way to do this used to be with a lot of care & attention in Photoshop, but in the past few years I've just left that behind as it's become too tedious compared to dedicated software.

There are some online (pay per image) sites that can even extract a subject with surprising accuracy even if it wasn't shot against a plain background.
Search "extract object from image online" to find a whole bunch of these. They usually do low-rez freebies or a few full-quality as a trial before taking your money. You might even find them good enough to pay rather than do it manually. Your call. I've tried a couple of them on just phone photos & they are surprisingly good.

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  • I think that the reason blue was used is that older types of film were less sensitive to blue light, so the blue background simply didn't register; no editing needed. – Pete Becker Jan 5 at 16:20
  • They use blue to this day. I think it may be a deeper blue than in the old Superman days, but I never saw it in real-life back then. I see it all the time these days; I work in the movie industry ;) – Tetsujin Jan 5 at 16:24
  • I found this magazine article with lots of pics including both blue & green for a movie I worked on a couple of years ago - vfxvoice.com/walking-a-tightrope-on-tim-burtons-dumbo Generally green is 'detail' blue is 'background'. Note both look very subdued in photos compared to in real life, possibly due to having that 'perfect single gun' they actually are & so might have had to be dialled back for the photos (or the still camera can't see them like eyes can, I really don't know how/why that is) – Tetsujin Jan 5 at 16:30
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    @PeteBecker, I don't actually know the old film-based blue screen process, but making film sensitive to blue light is easy. Making the film sensitive to red light was a technical challenge in the early 20th century. – Solomon Slow Jan 6 at 15:19
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    For movies: blue-screens were used because they were the farthest from skin tone and blue filmstock had smallest grain. Other variants like yellow screen were also used. Here's a good video for more information: youtube.com/watch?v=H8aoUXjSfsI – Matt Jan 7 at 14:46
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No, it doesn't have to be green. You can use any color that makes this easy to do. You probably don't want to use a neutral color, but rather something that contrasts pretty strongly with your dog.

The technique you're referring to is called chroma key. In order to make it easy to select only the background for removal, you want the background to be any color that's very dissimilar to any color in your subject. So if your dog is grey, any bright color should do. If your dog is brown, probably stay away from reds. Bright obnoxious green is used a lot traditionally because most clothing doesn't contain this color, especially on newscasters, where the technique is used extensively. For example, when the meteorologist stands in front of a map with the weather on it.

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    Actually if you use a mid grey background, it can make life a lot easier, if you want to change the background, but keep the shading of it. Photoshop's blend modes does wonders here, you will just have to mask the subject roughly. Of course, it can be a pain, if the subject is medium grey. – Kai Mattern Jan 5 at 16:10
  • @Kai Mattern - Thanks - I should have posted a picture. I have now. – chasly - supports Monica Jan 5 at 16:31
  • If you have the capability to control the light. A gray background can be illuminated to give nearly any color you may want or need. – user10216038 Jan 5 at 18:56

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