Graphics – pixels, dpi, color depth

Since we spend a lot of time staring at monitors and printouts, what they actually are is important. Let's start by talking about your monitor:

First step - how many little dots of light are shown on-screen. Each of these dots is called a pixel. Older monitors can't display much:

• CGA (320 X 180)
• EGA (640 X 350)
• VGA (640 X 480)
• SVGA (800 X 600 and larger). Everything you would purchase these days falls into this category.

These days, a 17" monitor is usually displaying 1024x768 pixels (at least those in our lab). With a larger/better monitor and better video card, this can go much higher. We call this the screen resolution.

Second step - color. Or color depth.

• 8 bit color. Only 256 different colors. Just fine for text, but photos don't look very good. You can set your system to this, but any newer system can handle far better.
• 16 bit color (called 'high color' on my system). About 65000 different colors. This is really plenty - your eyes can't resolve better than this. Uses two bytes (16 bits) to describe each color
• 24 bit color (called 'true color'). Uses 3 bytes (24 bits) to represent color. Around 16 million colors (16,777,216 to be exact).
• You can even get 32 bit color. Why? It just makes your video card work much harder for no apparent improvement.

Third step: DPI (dots per inch). Another way to think about this is pixels per inch.

Time for a little math. The viewing area of my monitor is 13" across. I'm running it at 1024x768. So: 1024/13= 78.77. Or, effectively, 79dpi. Not super high, but good enough.