The Truth About Resolution (how to understand pixels, etc.)

The Truth About Resolution Jesse Hemminger

Pixels pixels pixels, think in pixels, make all measurements in pixels. When we are talking about the resolution of a digital image we are talking about the number of pixels. A digital image is a virtual thing. It has no physical size. Its physical size changes depending on the display. Pixel count is a fixed property, no matter if we are looking at the image on my small laptop or projected on the wall the pixel count remains the same, while the pixels per inch changes from my laptop to the projection.

Higher Resolution = More Pixels

Standard monitor resolutions (all sizes in pixels)
1024 x 768 is most common monitor resolution. Other common sizes: 800x600, 1152x864, 1280x1024.
900 pixel max height and 600 pixel max width is a good maximum image size. This will fit on a standard 1024 x 768 monitor without scrolling, and leaves room for the menus and buttons at the top and sides.

You can go from big to small, you CANNOT go from small to big. Never enlarge an image, always rescan at a higher resolution (with more pixels). It is a good idea to always keep a high resolution (1800x1200) uncompressed copy of your image files. When you need an image for email or the web copy the file then shrink and compresses it.

Image size = how many pixels (pixel width and pixel height)
File size = how many bytes (how much space on hard drive)

Megapixels
pixel width x pixel height = pixels
1,000,000 pixels = 1 megapixel
EXAMPLE: 1800 x 1200 = 2,160,000 pixels = 2.1 megapixels

dpi x inches = pixels
On the computer dpi (dots per inch) is meaningless without also knowing how many inches. Inches is meaningless with out also knowing the dpi. DPI and inches both refer to physical space, a computer file is virtual.
EXAMPLE: if you have a 4 in. x 6 in. image scanned at 200 dpi, the digital image size would be 1200 pixels x 1800 pixels.

JPG compression, great for making file size smaller. For most fine art uses you will want to use medium or high quality jpg compression. The lower the quality the more digital artifacts will be introduced to the image.


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