ChromaPIX FAQ: (Frequently-Asked Questions)

I'm using a European version of Windows, and I can't get the slant adjusted.

Since ChromaPIX is "internationally aware", it expects to see and use the correct symbol for the decimal point for your language.  For example, in Italian or German, it must be "," (comma) .  In American English, it must be "."  (period).

To check this, launch the "Regional Settings" applet from Control Panel, and click the "Number" tab.  The "Decimal Symbol" should be set to whatever is correct for your country and language version.

I can't receive images in FAX480 mode.

In order to receive in FAX480, you must first select it as the current mode. This was done to conserve CPU time, and to provide a division between SSTV and FAX modes. The other "side of the coin" is that if FAX480 is the selected mode, ChromaPIX will only start in that mode.

ChromaPIX occasionally crashes when I select the Preferences window, and at some other times.

If you're running a product like 'First Aid' or 'Crash Doctor', you may need to disable it. Those products don't work well with real-time-priority applications like ChromaPIX.

I have a Creative Labs "SoundBlaster 16", and ChromaPIX crashes when I try to transmit, or sometimes when I exit the program.

The most likely reason for this is that you need to update the driver software for your card. Some of the "full duplex" drivers that were released on Creative Labs CD's could cause that to happen. If so, you can always get the latest drivers for this card from Creative Labs.

When ChromaPIX starts, it displays an error in the "MM system". What's all that about?

That usually means that another application is using the soundcard; maybe Windows itself. The most common thing to check is if you have Windows set up to play a sound whenever you launch a program. If that sound is long enough, Windows will still have the sound card busy when ChromaPIX first tries to use it.

I can't get ChromaPIX to work right.. I'm running 256 colors, by the way.

Here's the straight scoop:
Although ChromaPIX does support 256-color operation, it requires a pretty fast computer to do it. The reason is that the screen objects are kept internally in 24-bit TrueColor, and must be converted to 256-color for display. (This includes the spectral display, which is updated several times a second) Why? Because TrueColor is required for photo-quality SSTV, and times have changed. If your computer meets the hardware requirements otherwise, why cripple it with an obsolete video card?

I have a "586" processor, and ChromaPIX is sluggish, and doesn't respond well.

Unfortunately, there is a common misconception that "586" processors are equivalent to Pentiums. They aren't. A 90-mhz Pentium on a correctly-designed motherboard will run ChromaPIX just fine, while a "586" processor, even at a faster clock speed, will probably be sluggish. The same can be said for "accelerator" modules that allow you to use Pentium chips on a 486 or "586" motherboard. While they may be better than what was in there originally, they won't perform nearly as well as a Pentium chip on a motherboard that's designed for it, and includes a PCI bus. The problem is that the processor has to sit around and wait for many cycles, while the older style ISA/VLB peripherals finish their work.

Why won't my radio key up when I click the Transmit button? I have the RS232 interface I built for W95SSTV.

As of version 0.90.04, ChromaPIX supports RS232 push-to-talk control. To enable it, select Preferences from the Settings menu, then click the SSTV tab. You can select the COM port, (COM1-8 supported) and whether you wish to use the RTS or DTR line for PTT control. The interface below is a simple single-transistor switch, which can be used with the program.

If you have an older radio, or one that uses a higher-than-normal switching current, we recommend using an NPN "Darlington" type transistor, such as a TIP-120. No other component changes are required. For more interface information, please take a look at the Technical Corner section.

I hear people talking about "Martin 1", "Scottie 1", "Scottie 2", etc. What is all that about?

What they're referring to is different modes of transmission. An in-depth study of SSTV modes would take a lot more room than we have here, but in general terms, there are several "families" of SSTV modes, each with different characteristics. Each mode family has a number of "sub-modes", that normally differ in the length of the transmission time. Again in general, the longer it takes to transmit a picture, the better the results will be. In the US, for example, "Scottie 1" has become the most common SSTV mode, with a transmission time of ~112 seconds. When short transmission times are more important than quality, (like during an HF SSTV net) SSTV pictures will often be replayed in Scottie 2, which takes only ~72 seconds. For a more in-depth look at the history of SSTV, modes, and operation, we'll refer you to John Langner's excellent SSTV site.

I see DSP filters, DSP-based radios, and now you have a DSP-based SSTV program. What is all this DSP stuff, anyway?

DSP, or Digital Signal Processing is simply the science of using numerical functions on a computer to perform tasks which traditionally required analog components, such as mixers, delay lines, phase-shifters, filters, oscillators, demodulators, etc. A number of companies make specialized microprocessors for DSP work. You'll find them in cellular telephones, modems, radio gear, and test equipment, to name just a few. ChromaPIX works in exactly the same way as these devices, except that the DSP VM, or "virtual machine" uses the sound card and non-dedicated microprocessor in your computer, sharing time with other programs and the operating system. This "soft" approach to DSP has many potential applications for both amateur and commercial products. We chose SSTV to start with, because it's our favorite! As more and faster computers find their way into the ham shack, you'll see those computers performing more functions that used to require specialized equipment. There are, of course, both "pros" and "cons" to this approach, but one thing is certain: "Numerical" components don't leak, change value, drift, burn, or simply expire with age! :-)

The author would like to acknowledge Eric Wicklund, KR7A, for his pioneer work in applying modern DSP methods to SSTV systems.

If there is something you'd like to see posted in the ChromaPIX FAQ, please let us know!