How to customize gamma table of Electrohome VistaPro Plus


The projector has two internal gamma tables, called table #0 and table #1.

Each table contains 256 entries. The entries are numbered from 0 to 255, which represent signal input levels.

Each entry is assigned a value within the range of 0 to 4095. These 12-bit values represent light output levels. Typically, entry #0 is assigned a value of 0 (which represents the minimum light output level), and entry #255 is assigned a value of 4095 (which represents the maximum light output level). As an example, entry #127 could be assigned a value of 717 (which represents 17.5% light output level, since 717 / 4095 = 0.175).

Basically, the table tells the projector how to convert a signal input level into a light output level. You can assign your own values to either table by sending RS-232 serial commands to the projector from a PC.

Each command has the format:
(DGN? 4 4 10 T 3 E 1 M L)
where T is the table number (0 or 1), E is the entry number (0 to 255), M is the most significant 4 bits of the value (0 to 15), and L is the least significant 8 bits of the value (0 to 255). Commands are not case-sensitive, so "DGN" or "dgn" will work.

For example, to assign a value of 717 to entry #127 in table #1, you would send the command:
(DGN? 4 4 10 1 3 127 1 2 205)
since M*256 + L = 2*256 + 205 = 717.

After all the commands have been sent in order to assign values, you can send the following command, which tells the projector to start using the new values:
(DGN? 4 4 11 T)
where T is the table number to use. The projected image will change immediately. You can even switch back and forth between the two tables.

By the way, after you send each command to the projector, the projector sends the following reply in order to confirm that the command was received and processed:
(DGN!001)

Be careful not to send the commands too fast, or else the buffer will overflow and the projector will miss some commands. It is a good idea to wait for the projector's reply before sending the next command. In my experience, 256 commands can be sent in just over a minute, i.e., about 4 per second.

When you power off the projector, it loses all of the new values. So the next time you power it on, it automatically uses the default values, and you must resend the commands in order to use the new values again.

Feel free to download gamma.txt, which is a sample list of commands. To send them, you can use HyperTerminal, which is located under Start Menu / Programs / Accessories / Communications in Microsoft Windows. Make sure that Line delay is at least 250 milliseconds, which is located under File / Properties / Settings / ASCII Setup in HyperTerminal. After you establish a connection to the projector, select Transfer / Send Text File, and open the gamma.txt file.

The following document explains how to use RS-232 serial commands in general.

Vista Pro and VistaGraphx RS232 Commands (in PDF format)

This web page was created by Erik Garci.