jbhuber@IASTATE.EDU (Huber Joseph Blaine) (06/16/91)
Greetings. I recently obtained a program to convert .ppm files to sixel images for display on vt340 terminals (16 colors at a time). All I have is a vt241 (4 colors at a time), but I gave the program a shot anyway. I am displaying infrared sattelite images, which are mostly black and white with various shades of gray. With my vt241 in mono mode, I display the images. Three colors show up: black, white, and grey. The image actually looks pretty good. Then, once I just happened to push the setup key while the image was on the screen. the setup menu showed up, and the colors in the portion of the image that remained on the screen inverted: (i.e. white became black etc), **AND** another shade of grey appeared, adding incredible detail to the image (the detail was legitimate, I have a picture of what the image should look like). when I pressed the setup key again, the image reverted to its original three colors. I set the vt241 to color mode. I got the same black-gray-white image. When I pressed the setup key this time, the image that remained on the screen was a 4 color black-red-green-blue image (correct detail). If I go into setup while the three color black-grey-white image is writing on the screen and cyle through the mono-color-color+mono-mono option under the display menu and leave setup, the remainder of the image is displayed in four colors :white-lightgrey-darkgrey-black (or red-green-blue-black , if I stop on one of the color options), except that what should be black is white etc. (the colors are inverted). WHAT IS GOING ON HERE?? Why doesn't the terminal display the four colors initially, it seems to know that the image should be drawn in four colors (pressing setup causes four colors to display). I repeated this on a number of vt241's. The images display correctly on vt340's. Another question: before the sixel image begins to draw, the screen is made completely white. What causes this? I've looked at the sixel commands in the file, but i didn't see anything that should casue this. 16 colors are defined in the output file from the conversion program. Do I need to modify the the conversion program to write only a 4 color map for the vt240? Any help from the vt240/vt340/sixel experts out there would be greatly appreciated. I am new at this sixel business and the vt240 manuals that I have access to aren't terribly helpful in explaining what goes on in the terminal during sixel graphics writes. E-mail respones or postings to this newsgroup are both fine. Also please let me know if there may be a better place to post this plea for help. Joe Huber jbhuber@iastate.edu Dept. of Mech. Egr. Iowa State University