Subtract

[stingray]

i've had this idea for quite a while, since I was thinking about special effects for a short film i was involved with, very low budget of course...
My interest has turned now towards still photograph and I do most of my "arty" work on film. However I do extensively use a digital camera and photoshop.
My question concerns masking a photo to exxtract the subject from the background.
My idea is to take a photo of the background (tripod) then stick the person/thing in front of it with same exposure. Then armed with your two photos go into photoshopor something of the sort and subtract one from the other to leave the subject.
presumably if the images are exactly, or as close to exact as possible minus the subject in one, thgere should be sufficient information to create a mask of the subject. This would allow for many cool things to be done very easily. I really can't afford a greenscreen.
Thanks very much to anyone who knows the means to do this. :hail:
Regards, Willy.

 

[Big Mike]

I'm not quite sure what you want to do here...but you can extract a subject from an image without making two exposures. If you were using two exposures, you could extract the subject from one and then insert it into the other image...giving you two subjects.

While it is easier to extract someone from a green (or whatever) screen background. You can do it with any contrasting background. There are many ways to do it. Some sort of mask is usually the best way because you can 'paint' to give or take...fine tuning the mask.

Try the extraction filter, it's a good place to start.

 

[orangetree]

true the extraction filter is an excellent place to start. If you cant afford a green screen can you afford a white sheet... as long as there isnt white in your subject it makes it very simple to remove the background from a white one...

as far as using 2 exposures one with and one with out the subject... i will experiment with this idea... i never thought of using this method, but if there is some color exactly the same in the subject as in the background it will remove that too... Still thinkin on this one

 

[stingray]

i don't mind saying i'm very well learned in photoshop... so i have made masks conventionally hundreds of times in the past.. this idea appeals to me greatly because it doesn't rely upon having a chroma keyed screen or as you said a white, black or otherwise. The idea would be that shot 1 is a person on a background and shot 2 iis just the background. The idea would be essentially like a Boolean compound idea, the remaindered pixels would become their own layer leaving just the person/subject.