This applet demonstrates one use of the alpha channel for blending images. It really works well for me on an HP 715/100 using Netscape 3.0. You'll probably need Netscape 3.0 or Internet Explorer 3.0 to run it. Why isn't anyone using this for image fusion? Or are they?

Using the Alpha Channel: Brain CT-SPECT Overlay

The applet is on the far left. The middle image is the original CT scan (with edges). The right image is the original SPECT scan (with edges).

The CT scan is in gray. The SPECT scan is the color overlay.
Move the SPECT scan by either:

Pressing and holding the left mouse button while dragging the mouse
Using the arrow keys (or the h,j,k,l keys)


%	%	CT Scan with Edges	SPECT Scan with Edges

The "Alpha" button controls the percentage opacity of the SPECT image. The "Threshold" is the percentage at which to set a pixel totally transparent.

To Do:

Scaling of the overlay image in width and/or height.
An interactive box that clips the overlay image to only display within the box.
Labeling the moves with the overlay.

Here is the source code.

Image Credits

I am using these images with the kind permission of the Centre of Medical Imaging Research University of Leeds. They are taken from an excellent paper on "3D Registration of SPECT and CT Brain Images" by Dr. Bill Crum. Please read it if you're interested in automated methods for performing this alignment.

Created 10/05/96 by Andrew Barclay, abb@nuccard.eushc.org
Updated 12/18/96 by abb@nuccard.eushc.org