Stereo Image Compositing Utility

This note describes the use of a stereo image compositing utility available from StereoGraphics. This utility is intended to offer an elementary means for stereographers to translate existing pairs of left/right stereo images into composite interlaced format.

In order to view stereo images in Windows environments with SimulEyes glasses, the images must be composited in an interlaced video format. That is, the stereo image is composed of alternating lines of left and right image information which correspond to the even and odd numbered video scan lines. 

The composite interlaced stereo image is derived from a stereo pair of left and right images. These may have been created by a stereo camera as a pair of photographs, or generated by 3D rendering software as a pair of computer graphics images. In any case, the source images are coupled as a pair with compatible dimensions and color information.

One manual technique which has been employed is to use graphics manipulation software (like Adobe Photoshop) for compositing. A complementary pair of alternating line masks is applied to the pair of left and right images. Once masked, the left and right images are overlaid each other, so that only alternating lines of visible information remains.

COMBINE is a command-line utility which performs the interlacing operation on BMP image files, with optional horizontal and vertical adjustments. (StereoGraphics is also investigating visually-oriented compositing tools.)

COMBINE takes two BMP image files in 8-bit color format, and produces a composite interlaced BMP file in compatible format. 

The typical usage of COMBINE expects command line parameters with the names of the left image file, right image file, and composite output file. 

	combine left.bmp right.bmp composit.bmp

If the stereographer is working with many stereo image pairs, the command line may be shortened to expect a uniform naming convention. The abbreviated version expects the name of the left eye image ending with the letter “l” and the right eye image ending with “r”.

	combine imagel.bmp 


While there are many other graphics file formats available (like TIFF, GIF, JPEG, etc), the BMP format is chosen as the common denominator for its simplicity and its built-in support by Windows applications. Graphics software frequently offer BMP as a Save-File output. The stereographer may also use a graphics file conversion utility (like De-Babelizer) to obtain BMP format files.

In order to create a composite stereo image with optimal depth sense, it may be necessary for the stereographer to adjust the relative horizontal adjustment between the left and right images. This is entered as the first number-only parameter. 

	combine left right composit 10
	combine imagel -20

It may also be necessary to make a vertical adjustment for left/right image alignment purposes. This might be the case if the stereo pair were created from photographs. The relative vertical adjustment is entered as the second number-only parameter. 

	combine left right composit 10 5
	combine imagel 0 -2

The stereographer may download the COMBINE utility and example BMP files from the StereoGraphics FTP site at:

	ftp://ftp.stereographics.com/Outgoing

The available ZIP files are:

	comp16.zip = 16-bit COMBINE.EXE
	comp32.zip = 32-bit COMBINE.EXE for Win95/NT shell
	testbmp.zip = left and right BMP images

For further questions, contact 

	se-supt@crystaleye.com