A simple, (and primitive) way of doing this is to use the magic wand tool and playing with the tollerances until it selects what you need then adding a selection feather of 2 to neaten up the image then invert the selection and use CTRL+DEL to apply the background colour. Or delete to a transparency to apply a picture.
Martin,
Or you might try a Select> Color Range and select into the white background and play with the Fuzziness until you get about what you want. After you make the white selection you will want to edit to exclude non-background white things like the whites of people’s eyes and eye highlights, teeth, etc. Then you can Fill your selection, or make color adjustments to it to get the background you want. There are also third party programs to make it easy to change selected colors in an image.
However, regardless of how you change the background color, the results are liable to look somewhat "fake" because of the phenomenon known as radiosity. Every illuminated object becomes a secondary light source. If you change the background to red, then a real red background would have reflected some red light onto your subject. But your subject still shows the radiosity effects of a white background. With a little experience you can add the effects of radiosity to your subject in Photoshop. Incidentally, have you looked at Corel’s KnockOut plugin for Photoshop?
— Burton —
Burton, this "radiosity",
Near the end of a composite, I take a sampling colour directly of the light source (or predominant desired colour which is cast) and then I apply the lighting filter to try to match it up using Painter or Photoshop filters. This always is near the end of the project. Likewise, I have to add…colored shadows via the "multiply mode" as I build a composite. (I even take a picture of bulbs to try to help myself out later.)
Are you suggesting that a sample of the colour cast …can be located near the edge of subject from light reflection, a good location near an object which was cast from the light source? I mean that there is literally a ‘best location’ to swipe at with the sampler that will tell me in which direction to go?
This is of interest for me and I ask as it is something I still find difficult…indentifying the colour of subtlety.
Terrat,
Your procedure is probably "good enough" at simulating radiosity. It could be refined by additional radiosity light sources. But an exact simulation of radiosity isn’t always a good thing. For example, there might be a big blue surface off-camera that casts a significant amount of blue illumination on the subject. Since the viewer can’t see the blue surface, its effects can be counter-intuitive.
Artists are advised to paint from life to capture the nuances of lighting, including radiosity. A good 3D program can let you set up a 3D model and specify various primary lighting sources. Then its lengthy calculations can do a very good job of simulating reality.
Of course, the best simulation is reality. But frequently reality isn’t handy or feasible and the 3D program is "the next best thing." After you have studied lighting effects in detail, from life situations and from 3D programs, you will get "an artist’s eye" for various lighting effects, including radiosity, and you can add plausible effects of radiosity in Photoshop as you have done.
— Burton —
