· How to use graphics and images

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Resolution

Higher resolution means more dots per inch, means the dots are smaller.

The dots of "dots per inch" can be thought of as the individual elements of the picture. These dots, or picture elements are referred to as pixels.

Scanning resolution and printing resolution, at 100% scale, they are the same. Scanned resolution is what creates the actual image size. If the original has an area of 4 by 4 inches, that was scanned at 300 dpi, the image created is X by Y pixels now, 1200x1200 pixels. If you scale the image to print 8 by 8 inches, the printing resolution would be 150 dpi because you have spread the 1200 pixels across 8 inches.

A resolution arithmetic example -- if you scan 5x4 inches and print it half size to be 2.5x2 inches, and if you want to achieve 150 dpi on printed output, then you scan at half that, or 75 dpi. Because 5x4 inches scanned at 75 dpi gives an image size of (5 x 75) x (4 x 75) = 375x300 pixels. Scaling to print this at 150 dpi gives 2.5 x 2 inches, because 375/150 = 2.5 inches and 300/150 = 2 inches.

Color prints are only printed at about 200 dpi maximum. There is no reason to scan prints at a higher resolution. Negatives and slides are printed at resolutions of about 2000 dpi.

Onscreen display resolution is about 75 dpi. BUT, dpi doesn't really translate to inches and image size when displayed onscreen. Our monitors show a fixed area of pixels, which is usually 640x480 or 800x600 or 1024x768. Pixel size onscreen is determined by the current display settings of the workstation. The number of dots in the image will remain constant. Displayed at 640x480 screen resolution the pixels/dots will be bigger and result in a larger onscreen image than when the screen resolution is set to 1024x768 and the pixels/dots on screen are smaller. Likewise, scanning an image in at a higher resolution will result in more dots in the image. More dots to be displayed onscreen will result in a larger displayed image size.

So A 3x5 inch image scanned in at 75 dpi resolution contains fewer pixels than the same image scanned in at 150 dpi resolution.
When displayed onscreen the higher resolution image contains more dots so it will occupy more area onscreen.

For some examples and further explanation, see: http://www.scantips.com/interpol.html

If an image is enlarged/resized after scanning, the graphics program doing the enlarging has to make up information, manufacture pixels based on the original pixels. You could think of it as each individual, original pixel, getting bigger, therefore, resolution is decreased.

Resampling vs. Scaling -- Resampling is a very drastic change. Every single pixel is torn down and rebuilt. Actually, it's replaced with an approximation of others nearby. Scaling is not a change affecting the image pixels at all, rather, it affects the spacing of the original pixels on the printed paper. The original pixels are

How to Use Graphics and Images

A few informative Web sites:

Resolution