"Color Depth" refers to the number of colors that your system is configured to display. The personal computing world has progressed from monocolor displays during its infancy to the richness of "True Color" available with today"s moderately priced hardware. You have the following color depth options with current Windows operating systems:

Notice the correlation? The preceding table is meant to illustrate that the number of possible colors increases exponentially relative to the number of bits of video memory used for each pixel. You knew that already? It does work nicely, doesn’t it? What may not be readily obvious are the hardware requirements of your configuration. The following table illustrates the video memory required at various screen resolutions for all color depths

If you are reading this article, chances are that you have clicked the "Settings" tab of the "Display Properties" dialog in Windows 95, 98 or NT 4.0. Perhaps you did not realize that the "Colors" and "Screen Area" limitations are a result, first and foremost, of the amount of video memory in your system. Let’s assume you are operating a PC with 2Mb of video memory at an 800 x 600 resolution at a color depth of 16.7 million colors. If you tried kicking up the resolution to 1024 x 768, the operating system dropped the color depth automatically to 16 bits since there was no way it could possibly pump out the required amount of pixels for a 24 bit color depth. And then you tried 1280 x 1024 and discovered, "Bummer, I can only run 256 colors at this resolution on my big, bad monitor!?"

What is going on here? Well, Windows outputs everything you see and manipulate on your monitor as a bitmap. Every button, scroll bar, toolbar, etc., everything is a bitmap. In spite of the fact that you may be viewing a compressed 1024 x 768, 24-bit, JPEG image (all JPEG files are compressed and 24 bits) that occupies only 250Kb on your hard disk, the operating system has "decompressed" the image so that it occupies 2,304Kb of video RAM. Big difference...and more than a few CPU clock cycles were utilized in the decompression. While using compressed image formats for transmission over a company intranet or the world wide web makes a lot of sense, are you willing to incur the performance hit of decompressing multiple, compressed images on one screen in an Industrial PC on the factory floor? In fact, many high-performance games and multimedia applications have utilized images with a 256-color palette or less whenever possible due to these very issues. We'll cover palettes in the next article.

Current technology and pricing may very well render these issues as unimportant in the very near future. But given a preference, I would opt for performance over style any day of the week. In the world of Industrial Automation, responsiveness to the process should be of paramount importance to the software designer or design engineer. Knowing the end user’s hardware is a definite advantage for delivering a high-performance app. Maybe a true color image will be best in your situation. However, you should know that the human eye cannot detect every single one of the 16.7 million colors that a PC can display. Moreover, many video cards and monitors are simply incapable of rendering every single "True Color". In general, if you want your application to seem agile and well designed, reduce the color depth in your images whenever possible, preferrably to no more than 256 colors. All the robust and efficient code, scripting, and well-designed databases cannot overcome "image bloat" on a PC with a substandard graphics subsystem.