Writing PNG Images to File from Command Line

Howdy, Because of some latency issues in the display of dynamically created PNG images, I've been trying to separate the image-creation process from the image-display process. Essentially, I'm trying to run a cron job that writes a PNG image to file every 5 seconds. The php file pulls data from a MySQL db and creates a color-coded map of a cancer treatment building. The presence of normal levels of Neutrons would lead to the creation of a green flag, above-normal levels yields a yellow flag, and high levels yields a red flag. Another page will simply use a SRC tag to display the image, and will refresh every 5-6 seconds to get the latest readings/image. The concept worked extremely well when the image was output to the browser, except for the fact that a latency caused the image in the browser to flicker when it refreshed. So I've attempted the above, but without success, in that I can't get the cron job to actually make the image file. I know that the file is being processed because I can echo out a few words to the screen. And I know that the php file can create an image file because it does so when I add the file_name attribute to the imagecreate() function. I've checked permissions on folders, etc, and have tried both the CLI and SAPI versions of php, with and without available command line flags, but no luck. And it's not the db query portion of the process because I've commented out that portion of the code. Pretty much stumped and very open to thoughts/comments. The Set Up: RH 9.0 Apache 2.0.48 PHP 4.3.4 Mozilla 1.5 (MySQL 4.0.18) Thanks, David