Photoshop
Digital Graphics
Computer Monitors
Understanding how a monitor displays digital graphics will help you relate what you do in Photoshop to the end result displayed on the screen. It's also essential in the task of Web design. Knowing what determines the display size of an image is important when making decisions on sizing graphics and other Web content.
Monitor Phosphors and Pixels
Computer monitors display digital images by illuminating tiny dots in the screen called phosphors. This image shows phosphors that have been greatly magnified. A triad of red, green and blue phosphors is what makes up a pixel (picture element).
Different combinations of phosphor colours create the colour of an individual pixel. In this example, the area that has been magnified was actually taken from a grey area of the button. While it looks colourful close up, at its regular size the colours neutralize each other, emitting the colour grey. We'll explore this in greater detail in the Colour Space lecture.
Monitor Resolution
Pixels are arranged in rows and columns on a monitor screen. The number of pixels displayed in these rows and columns is determined by the monitor's resolution. Monitor resolution is expressed by the number of pixels across by the number of pixels down (width x height). Typical monitor resolutions are 640 x 480, 800 x 600, 1024 x 768.
When you buy a monitor, it will have a maximum resolution capability. Let's say you have a monitor that can display up to 1024 x 768. You can adjust the monitor settings to display lower resolutions which will resize your desktop. If you've ever adjusted the monitor resolution, you probably noticed that text and images appear smaller at higher resolutions. This concept is important when you are working in Photoshop and are designing images for the Web.
Resolution and Image Size
| Monitor Resolutions - All displaying same 640 x 480 image | |
|---|---|
 |
 |
| 640 x 480 | 800 x 600 |
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|
| 1024 x 768 | |
The examples above illustrate the point that the size a single image will display on the screen depends on the screen (or monitor) resolution. The dimensions of the sample image were 640 pixels wide by 480 pixels high. Each pixel in the image needs one screen pixel to display it. On a screen set to 640 x 480, there are just enough pixels to display our 640 x 480 image so it fills the screen. On a screen set to 800 x 600, there is room left over around the image and on a 1024 x 768 screen there is even more room. Therefore, with each increase in screen resolution, the image appears smaller. From this we can draw the conclusion that pixels are smaller on monitors with higher resolutions. This, however, doesn't mean that resizing the desktop changes the size of the monitor's pixels. The pixel size is fixed in each monitor. Resizing the desktop only changes your view of the pixel size.
Computer Monitors Summary
- Computer monitors display digital images by illuminating tiny dots in the screen called phosphors.
- A triad of red, green and blue phosphors is what makes up a pixel (short for picture element).
- The combination of colours in a given triad of phosphors is what creates the colour of an individual pixel.
- The number of pixels displayed in rows and columns on a computer's monitor is what determines the monitor's resolution.
- Each monitor has its own maximum resolution. You can resize the desktop to display lower resolutions.
- Images displayed at higher monitor resolutions appear smaller than at lower resolutions.
- When describing the number of pixels per square inch that a monitor is capable of displaying, the term ppi (pixels per inch) is used. Macintosh computers typically display 72 ppi and PCs display around 96 ppi.
- Identical images or Web pages will display larger on a Mac than on a PC because of the difference in their ppi values.
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