This is most important part of the Maskerade process. In order for Maskerade to do a really super job, it needs to do accurate compensation for uneven background lighting. In order for this to happen, you need to identify the lightest and darkest points of the visible background in one of the source images. These two points act to specify any lighting gradient that may have occured across the background.
Note:
The two points that you specify are common between the source images. This means that once you have set the two points on image #1, they will appear in the same locations on image #2. If you switch to image #2 and move the points, they will move in image #1.
The reason for this is simple. When you physically change the backdrop from light to dark without changing the illumination on it, the lighting gradients on the backdrop material will be similar for the two shots. When you change the backdrop brightness through illumination, you may have a lighting gradient in one shot but no gradient in the other. In either scenario, the identification of a single lighting gradient is all that is necessary.It's really easier than it sounds. You need to use the 'Color Readout' to identify the lightest and darkest areas of the background in one image. Switch to the image that has the most visible gradient across its background. This is usually most noticeable in the image with the lighter background, assuming the background has not been clipped to pure white in most areas. In some cases though, the darker image will have a light enough background that the gradient is most visible in it. Use whichever image gives you the most information to make this decision. Zoom out so that you can see as much of the source image as possible. Simply move the cursor around watching for the brightest and darkest areas. Use the following images as an example.
Once you have identified the lightest and darkest points in one of the images, simply select the 'Eyedropper Tool'
and click in the image in the two areas you have identified.
Tech Tip:
The marker points define a 5x5 area which is averaged to obtain the color of the point you select. This averages out the effects of image noise and/or film grain, so you do not need to be critical of your exact point locations.If no points are defined when your source images are opened, the first two clicks you make will define two new points. After that, any clicks with the 'Eyedropper Tool' will move the existing points to new locations. If you click away from either of the point markers and drag, the marker closest to where you click will be moved. You can move a specific point marker by clicking on it and dragging it to a new location.