STACKING VIDEO CAPTURE IMAGES:
A PRIMER
by Jim Ferreira
.
The stacking of images can significantly reduce the grainy appearance of captured video images and improve contrast between dark and light features, thus improving apparent sharpness.  Stacking images also eliminates much of the random noise and artifacts.  Only those features that appear in each image will remain after stacking a half dozen or more images together.

The accurate stacking of images does not require a highly sophisticated pieces of software such as PhotoShop, Mega-Fix, QMiPs or Maxium.  Stacking can be done quickly and effectively with the Adobe Photo-Deluxe (PD)software that comes with the Snappy frame grabber.  After familiarizing one self with opening and saving image files, it is only a matter of performing a few straight forward steps to stack an unlimited number of images.

The assumption is made here that images have already been captured to computer memory and can be accessed by the PD program.  It is recommended that images be captured at at least 600x800 or higher resolution and be stored in a non-compressing file format such as TIFF.
 
1 )  The first step is to go to PD FILE MENU and scroll down to PREFERENCES.  There click on the ALLOW MULTIPLE DOCUMENT WINDOWS.  You can now open two image files one at a time using the GET PHOTO command.  Adjust the window/image size with the +/- buttons so that both can be seen in entirety.
2 )  Now go to the menu bar and select VIEW and scroll down to SHOW LAYERS.  Select one of the two image windows, then go to the menu bar and select EFFECTS and scroll down to NEGATIVE.  The image in the selected window will change as seen at left.  Next go to the LAYERS window and double click on the thumb-nail image -- change OPACITY to 50%, then OK.
3 )  Now go up to the menu bar and click SELECT, scroll down to SELECTION TOOLS, then to MOVE (or CRL 'G').  You now can move the negative image into the window with the positive image by placing the cursor over the negative image, holding down the left button and dragging image over on top of the positive image.
4 )  Using the ARROW KEYS you can now move the negative image one pixel at a time across the positive image.  Overlap the two images and adjust until both images completely merge and cancel each other out.  Do not rotate image.  Because the images are not identical, there will still be some texture visible -- try to reduce the dark/light texture to the absolute minimum using the ARROW KEYS
5 )  Once satisfied the images are sufficiently aligned go up to the menu bar and select EFFECTS, scroll down and click on NEGATIVE again.  The top image will return to positive, now contributing 50% to the image information, as at left.  Go to the LAYERS window and click the right pointing ARROW, then click MERGE LAYERS.  The two layers are combined into a single image.  Next close the window containing the negative image -- do not save.  The original image file will not be effected and remains saved.
6 ) The next image can now be opened beside the window containing the stacked image and the process can be begun again by making the new image negative and 50% opacity and dragging over onto the stacked image.  After each stacking, merge layers.  Any number of images can be stacked in this manner.  Graininess will continue to be reduced and apparent contrast and sharpness will improve with each new layer.
7 )  Brightness, contrast and sharpness can now be adjusted using the PD program or saving the image as a TIFF and importing it into any image processing program.

PD does have an UNSHARP MASK command -- go to EFFECTS, then SHARPEN, then UNSHARP MASK.  Good initial setting would be 50-75% amount of sharpening, 2-6 pixel radius and threshold level near zero.  From image to image these settings will vary depending upon what details your are trying to enhance.  Be sure to experiment.
Should you run into difficulties or have questions feel free to contact me at ferreira1@llnl.gov.
 

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