This dialog box gives some statistics about the current active stereoscopic image.  The Resulting Stereo Image section is about the stereoscopic .PNG image composed with the right image followed by the left image with sometimes some padding pixels between them.

Size
Displays the size of the image.

Grayscale
Displays No if the image contains at least one colored pixel.
Displays Yes if the image contains only grayscale pixels.

Palette
Display Not applicable if the image is grayscale.
Displays No if the image contains more than 256 different colors.
Displays Yes if the image contains 256 or less different colors.

Alpha channel
Displays Uniform if the alpha channel contains all the same alpha value.
Displays Non-Uniform if the alpha channel contains different alpha values.
Displays Non-uniform but Palette Alpha if the total of alpha palette indexes is 256 or less.  (Each color palette index is associated to its corresponding alpha palette index.  By example, if a color has three different alpha values, the color palette will use three indexes for this color to associate them to the three different alpha values.)

Alpha color
Displays No if the alpha channel can not be created with an unique pixel color associated to the 0 alpha value.
Displays Yes if the alpha channel can be created with an unique pixel color associated to the 0 alpha value.

Left/Right Half Height Flag
When selected, this check box indicates that the left and right images contain only the half the total horizontal scan lines of the stereoscopic image they represent.  So the real stereoscopic image height is considered to be twice the height of the left image or right image.  This flag is useful to reduce file size for stereoscopic images that are intended to be viewed only with liquid crystal shuttle glasses.
Note: If you create a new stereoscopic image using left and right images having only the half of the horizontal scan lines, you must set this flag to able correct displaying of the stereoscopic image.  This is often the case of the left and right images contained in an interlaced image file.