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Digital Cameras

Digital cameras also have a resolution setting. This setting is just like the one used for your monitor, and all it means is how many pixels it will capture in the width and height of the image. It's measured in megapixels. That's just a fancy name for multiplying the image's width by height in pixels, and dividing by 1 million. Thus, a 1600-by-1200-pixel image is a 2 megapixel image (1600 multiplied by 1200 equals 1,920,000 pixels, which is approximately 2 million pixels).

When you open an image from a digital camera in Photoshop, Photoshop has to assign the image a resolution setting (ppi). It has no idea what you're going to use the image for, so it assigns 72, which is what an average computer monitor displays in each inch. If you print an image that has a resolution of 72 pixels per inch, it will most likely look pixelated (Figure 4.6). You can always change the image's resolution by choosing Image > Image Size. To do that, just uncheck the Resample Image check box in the Image Size dialog box, and then enter a new resolution setting. Photoshop will do some simple math (width in pixels divided by resolution = width in inches) to figure out how large the image will become with that setting (Figure 4.7).

Figure 4.6. An image with a resolution of 72 will usually look pixelated when printed.


Figure 4.7. If you change the resolution of the image when the Resample Image checkbox is unchecked, Photo shop will change the size of the pixels without changing how many pixels there are in the width and height of the image (in this case, the resolution was changed from 72 to 300).


If your digital camera doesn't record enough information for the print size and resolution you need, then you can use Photoshop to resample the image. Let's look at that term for a moment. Your scanner's resolution setting is expressed in samples per inch, and now you have a chance to resample your image. That would be like scanning an image, printing the scanned file, and then rescanning the printout with a different resolution setting. You'd end up with a different amount of information in the final file, but it would be based on the first file, not the original image. Lowering the resolution with resampling doesn't harm your image much because you're asking Photoshop to give you less information than that which your file already contains (Figures 4.8 and 4.9). But if you increase the resolution with resampling, then you're asking Photoshop to make up some extra information based on what's in your file (Figures 4.10 and ). It does that with math. In essence it averages the brightness of two pixels to determine the shade to use when it makes a new pixel. The math it's using is known as interpolation. Some people will say they resampled an image and others will say they interpolated it, but they are both talking about the same thing.

Figure 4.8. Original image scanned with a resolution of 72PPI. (© 2000 Stockbyte, www.stockbyte.com)


Figure 4.9. Image after resampling to a resolution of 300 ppi.


Figure 4.10. Original image scanned with a resolution of 600 ppi.


Figure 4.11. Image after resampling to a resolution of 300 ppi.


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