When you want to be somewhere else…
There are places we would rather be than where we are now. I would like to be on an island paradise …not going to happen! But you can do it photographically. The secret is something called Chroma Key photography or green screening.
Chroma Key Substitution
In chroma key, often known as “green screen” photography, the subject is photographed against a uniformly lit green background. Then, in post production the subject is easily selected out from the green background. The selection can then be pasted into any other photographic background.
Any uniform colour can be used as a backdrop for the chroma key shot. The picture above is selected from a blue background and pasted into a picture of Winchester Cathedral in SE England. The two pictures were taken on different days.
To make the selection of the subject from the background it is important to light the background evenly. When the colour is even the selection is easy and can be completed in one operation. Colour variations from uneven light make it more technical to isolate the subject.
Green is the most frequently used colour in chroma key photography. The colour is very easily separated from human skin tones. Where the subject has green tones, blue is often used as the chroma key alternative. Blue is a common colour for clothing. It is therefore less suitable than a strong bright green which is not so popular as a fashion colour. However, green does have other advantages. The human eye is able to see more shades of green than any other colour. This makes it easy to see variations in the green when setting up the lighting. Green sensitivity is also built into software applications to match the abilities of the eye. This helps us to work with the background when doing awkward selections.
Fun and games
The substitution of a subject into any other photographic background provides great opportunities for doing fun things. Film stars can be placed in your garden. You can apparently travel the world without leaving your front room. Just find the right pictures and substitute yourself into the background of your choice.
Of course there are also opportunities for advertising, graphic art, product photography, still life, portraiture, action shots and many other false situations. Of course we should be careful not to be immoral about such things! Feel free to have fun though. You can really make it look like you have traveled the world.
How is it done?
Basically you need a chroma key background, lighting to illuminate it evenly, a camera and a subject. On a small scale this is easy to do. A lot of people doing chroma key work for the first time start with still life or table-top photography to get the technique right. Probably the most common use of the technique is for portraiture. Take a picture of yourself or your friends and then start playing. For this you need a larger screen…
The video is a complete introduction to the use of chroma key photography. You can take the same techniques and scale them to any size. The video introduces the ideas you need to grasp and shows how to set up the lights and the equipment. It also shows one of the software applications. After the video I will briefly look at that software for you.
How to Green Screen (Chroma Key) with Photography!
There is a whole range of software that is capable of doing chroma key. In essence chroma key software has two jobs. The first is to select the subject off the green background (or whichever colour you are using). The second is to successfully blend the abstracted subject with the new background.
The software from the video is called PhotoKey from FXHome . It has been produced specifically for chroma key compositing. It is not alone in the market. However, there are not many applications specifically aimed at this work. Instead there are plenty of applications that do chroma key blending as part of a general suite of editing tools. There are also plugins for the same process to go into your favourite image editor.
The actual process for producing the final blended image is relatively quick and easy in most of these chroma key applications. The tools are usually quite self explanatory if you have some editing experience. As with any editor, you normally find the blending tools manage colours, contrasts, edging and so on. Ultimately you are creating a blend of the two images, but the best chroma key tools go further. At the end of working through the blending process you can make further changes in a good software suite or plugin. If you are satisfied with it you should be able to export your image to make a .png, .jpg or .tiff image.
The way to do it in Adobe PhotoShop
The general photographer is most likely to have use of a quality image editor like PhotoShop, Elements, GIMP, PaintShopPro and others. All these are able to do the type of work that PhotoKey can do. Admittedly it takes longer. But for beginners it is better to save your money for more general photography kit. For those who are interested, here is a short video explaining the Photoshop method of doing a chroma key composite. It is a simple technique using standard photoshop tools.
Isolating with a Chroma Key Background
This tutorial is aimed at Photoshop intermediate level users.
Chroma key work is fun. There is quite a lot to learn, but it adds flexibility to your photographic work and post processing. The use of up to date quality image editors is probably better than splashing out on expensive specialist applications. Nevertheless specialist applications do a great job, saving time in post processing.
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