Without a doubt, the number one thing you can do to improve your digital photos is to understand the concept of resolution. Unless you make the right choices about resolution, your pictures will be a disappointment, no matter how captivating the subject. In other words, donít skip this section!
Pixels: Building blocks of digital photos
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| A Sunday Afternoon on the Island of La Grande Jatte |
Have you ever seen the painting, A Sunday Afternoon on the Island of La Grande Jatte, by the French artist Georges Seurat? Seurat was a master of a technique known as pointillism, in which scenes are composed of millions of tiny dots of paint, created by dabbing the canvas with the tip of a paintbrush. When you stand across the room from a pointillist painting, the dots blend together, forming a seamless image. Only when you get up close to the canvas can you distinguish the individual dots.
Digital images work something like pointillist paintings. Rather than being made up of dots of paint, however, digital images are composed of tiny squares of color known as pixels. The term pixel is short for picture element.
If you magnify an image on-screen, you can make out the individual pixels, as shown in Figure 2-4. Zoom out on the image, and the pixels seem to blend together, just as when you step back from a pointillist painting.
Figure 2-4: Zooming in on a digital photo enables you to see the individual pixels.
Every digital photograph is born with a set number of pixels, which you control by using the capture settings on your digital camera. (See Chapter 5 for details.) Most cameras today can record at least one million pixels, and higher-end models can capture six megapixels or more.
Some people use the term pixel dimensions to refer to the number of pixels in an image - number of pixels wide by number of pixels high. Others use the term image size, which can lead to confusion because that term is also used to refer to the physical dimensions of the picture when printed (inches wide by inches tall). For the record, I use pixel dimensions to refer specifically to the pixel count and image size or print size to mean the print dimensions.
As I detail in the next few sections, the number of pixels affects three important aspects of a digital photo:
- The maximum size at which you can produce good prints
- The display size of the picture when viewed on a computer monitor or television screen
- The size of the image file
Pixels and print quality
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| Figure 2-5: Output resolution (ppi) affects print quality. |
Before you print an image, you use a control in your photo editor to specify an output resolution, which determines the number of pixels per inch (ppi) in the print. Figure 2-5 shows the control as it appears in Adobe Photoshop Elements 3 (Chapter 9 provides specifics).
Output resolution, which many people refer to as image resolution or simply resolution, plays a big role in determining the quality of your printed digital photos. The more pixels per inch - the higher the ppi - the crisper the picture, as illustrated by Figures 2-6 through 2-8. The first image has resolution of 300 ppi; the second, 150 ppi; and the third, 75 ppi.
300 ppi
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| Figure 2-6: A photo with an output resolution of 300 ppi looks terrific. |
150 ppi
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| Figure 2-7: At 150 ppi, the picture loses some sharpness and detail. |
75 ppi
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| Figure 2-8: Reducing the resolution to 75 ppi causes significant image degradation. |
Note that output resolution is measured in terms of pixels per linear inch, not square inch. So a resolution of 75 ppi means that you have 75 pixels horizontally and 75 pixels vertically, or 5625 pixels for each square inch of your printed image.
Why does the 75 ppi image in Figure 2-8 look so much worse than its higher resolution counterparts? Because at 75 ppi, the pixels are bigger. After all, if you divide an inch into 75 squares, the squares are significantly larger than if you divide the inch into 150 squares or 300 squares. And the bigger the pixel, the more easily your eye can figure out that itís really just looking at a bunch of squares. Areas that contain diagonal and curved lines, such as the edges of the coins and the handwritten lettering in the figure, take on a stair stepped appearance.
If you look closely at the black borders that surround Figures 2-6 through 2-8, you can get a clearer idea of how resolution affects pixel size. Each image sports a 2 pixel border. But the border in Figure 2-8 is twice as thick as the one in Figure 2-7 because a pixel at 75 ppi is twice as large as a pixel at 150 ppi. Similarly, the border around the 150 ppi image in Figure 2-7 is twice as wide as the border around the 300 ppi image in Figure 2-6.
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