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Combine Panel |
The Combine panel has settings that allow you to choose how the green areas found in the foreground image are to be treated.
A little bit of Green Screen removal theory will help you understand the controls.
Here are some conditions that we would need to consider:
- The green we see is coming directly from the screen. If this is true we want to replace it completely with the background color
- The green we see is a shadow coming from the screen. If this is true we want to remove it as well
- The green we see is passing through a semi-transparent area, like thin blond hair. If this is true we need to remove the green tint and make the area transparent.
- The green we see is reflected off of the surface of the image. If this is true we want to remove the green tint but not make it transparent
- The green we see is not from the screen but was some green in the original foreground. In this case we want to leave it alone.
Ok but how can we tell if it is a shadow or if it is some black hair in the photo? The simple answer is we can’t. We need the controls to tell us what is going on. Fortunately most of the time people have brown hair not actually black hair so the software does not get confused. Each control is designed to fix some problem that might occur. If you are not sure what to do the simple try moving each slide a bit to see it the picture gets better or worse.
The first two sliders Select Background Areas and Restore Dark Areas work together. If the green area in the foreground photo is very close to the computed background green then the area is completely removed and the background is shown at 100%. If the only green in the foreground image is the background green it is not very important where this slider is set.
If you look at the image shown above it seams as if some of the models hair is missing. That is because the Select Backgrounds Areas slider is removing it thinking that it is a shadow area on the screen. The Select background could be turned down or the second slider “Restore Dark Areas” could be turned up. In the case of black hair it is better to restore dark areas as this slide assumes that the areas are black and will remove any green tint found in the dark areas.
While you are not supposed to have anything green on, in some cases, if the green is a different enough shade, it can be restored in the image by change the green areas selected.
Notice how the green in the models blouse and the grapes has been restored.
If you turn the transparency down you can see that the green spill has made the blanket a bit transparent. We know that the blanket is not transparent so sliding the transparency slider to the right will make the blanket solid.
With the transparency slider to the right, the blanket now looks solid.
The Scale Transparent Areas slide changes the dynamic range of the transparence. If it is set too low all the items in the transparent areas will appear very transparent. If it is set to high then the less transparent areas will disappear and the semi- transparent areas will become solid. If it is set correctly then there will be a range of transparency values.
Perhaps an illustration will help.
Here the value is set too low. See how her hair seems to be too transparent.
Here the slider is set too high. The transparent areas have disappeared.
Here the slider is set correctly. Notice how her hair looks wispy not clumpy.
The advanced options:
The Add Transparent Areas will cause areas that are not green to be come transparent. Unfortunately it can make some part of the subject that should not be transparent be transparent as well.
Sometimes the software that computes the base green picks a green that is too bright or too dull. This Adjust Max Background slider will adjust that.
At the bottom of the page we see checkbox labeled “Show Selected Areas”. When this is clicked we see where Green Screen Wizard has selected background and where it thinks the foreground is. The green areas are the background. The pink areas are foreground areas where the red is greater then the blue. The blue areas are where blue is greater then red.
The gray areas are the transparent areas. The darker the color the more transparent the area is. One of the things to look for is very dark areas inside what we think is solid background. Some people have green eyes so we may want to set the Background Selection down or the transparency up.
If you see bright green areas in the background then that means that the setting for the Adjust Max Background is too low.
If you see dark areas in the background then you may need to move the “Select Backgrounds Area” slider more to the right. If sliding it to the right make all of the hair disappear then move it back some. The dark areas are often transparent so you should check to see the effect the slide is having by moving clicking and un-clicking this control.
To see the original foreground photo just check “Show Original Photo”.
