Light the green screen as evenly as possible
Its not always easy to have a perfectly lit green screen. However, you should try to avoid dark shadows whenever possible, Sometimes shadowing can't be avoided, For example, when doing a full body shot with the subject standing on the screen, there will be no way to avoid shadows. For this case, all areas of the screen should receive light by at least one flash source. A simple way to accomplish this is by using 2 flash strobes at an angle to the person (one to the right and one to the left). The area that is shadowed by one light is illuminated by the other. Since some screen areas are lit by 2 lights and other areas are lit by one light, there will still be some shadowing. However, this should be good enough to get a good extraction.
This diagram shows a simple set up for a single person portrait shot. For green screen portrait photography, we don't recommend lighting the screen separately or using back lighting on the model. Its just not needed and can give undesired results. Back lighting is common with video green screen and it can aid in the extractions. However, it can add unnatural lighting effects to the hair. Also, fine hair detail can be lost. For video, this is usually not that big of deal. However, for a portrait head shot still image, its better to NOT use the back lighting and keep more hair detail intact.
Our Easy Green Screen plug-in works very well when using a simple setup as shown in this diagram. Lower powered strobes (around 150 watt/second) will often work just fine. However, higher powered strobes will allow you to use a more narrow aperture and keep the entire subject in focus which helps with the image extraction process.
- White Balance: Set to Flash or Manual WB using a gray card
- ISO: Always use 100 - High ISO values have more noise. Higher noise can cause a speckled transparency mask on the extraction. This is because some of the pixels from the green screen are less green (or not green at all) with higher noise levels.
- Aperture - Use as narrow of an aperture setting as you can get away with based on your lighting and how the aperture affects the green screen exposure. A narrow aperture (high F number) will help keep the entire subject in focus, including individual hair strands, which will help the extraction be cleaner. However, when using too high of an f value, the entire image can start to get defocused due to diffraction. Basically, diffraction is caused by light bending when it goes through a narrow opening.
As a general rule for green screen, you want to use as high of an f value that you can before diffraction starts limiting the focus. For a full frame digital SLR camera, you can typically shoot with f16. For a 1.5x or 1.6x crop sensor digital SLR, you can typically use f11. For point and shoot cameras, you will need to shoot a lower f value, which will vary depending on the camera model itself. The actual f value that you can use is dependent on the actual size of the image sensor in the camera.
- Shutter speed - This doesn't matter too much with flash photography as long as the shutter is open long enough to compensate for any delay between the shutter and the remote flash. The exposure will be set with the flash intensity and not the shutter speed. 1/60 or 1/100 sec should work fine. You can go with a faster shutter as well as long as it is longer than the sync speed. Some remote flash systems cause longer sync speeds than the camera specs. You want to test this and know the actual combined sync speed for your set up.
Space your subject away from the green screen by 6 ft. or more if possible
The closer the subject is to the green screen, the more green spill that will be encountered. This is because the screen reflects green light back onto the person. Obviously, If you are doing an upper body shot, you will be able to space the person further away then if you are doing a full body shot. If you need for the person to stand or sit on the screen then try to use a screen that's long enough to cover sufficient floor area so that you can get decent spacing between the persons upper body and the back of the screen. Easy Green Screen does a pretty good job of green spill removal. However, its best to try to minimize the spill during the photo shoot.
Check the green screen exposure in Photoshop
Easy Green screen will automatically compensate for a variety of lighting conditions. You will however get the best results if you pay attention to how the screen is lit and adjust as needed. Use the adobe color picker to sample different areas of the screen.
The following numbers are what we consider optimal numbers.
sRGB color Profile: Hue=120-140, Sat=50-70, Brightness=50-60
Adobe 1998 color profile: Hue=105-125, Sat=50-70, Brightness=50-60
Minimize wrinkles in the screen whenever possible
If you have a stationary studio then this can be easily done by using a paper backdrop or a painted wall. If you are using a muslin green screen, then you will tend to have some wrinkles to deal with. Wrinkles can be ironed out (which is tedious).
To be honest, this is where we get lazy in our photo shoots. Since we do traveling photo shoots, using a large paper roll background is a bad option. Ironing out wrinkles isn't always an option either.
If your screen has some wrinkles then make sure to stretch the screen fairly well on the backdrop stand using some clamps so there are not any large folds. Also, make sure that light hits the screen from 2 angles. You should still be able to get a good extraction this way even with some wrinkles in the muslin.
Shoot in raw mode
This is not absolutely necessary. With that said, there are some big advantages.
First, there is not any .jpg compression. This is helpful when masking detailed areas.
Second, in-camera settings for the color profile, sharpening, toning, white balance, etc can be changed non-destructively because these are not directly applied to the image. They are just set points that are stored (similar to the Photoshop adjustment layers).