# Calculate Pixel Size

A calculator for the pixel dimensions of details in digitized maps. The map is e.g. digitized with a scanner. It is assumed that the pixels are quadratic. The resolution at scanning is commonly given in dpi, dots per inch, sometimes in dpc, dots per centimeter. This value, the pixel density, must be entered. The scale of the original map is needed to calculate the dimensions of one or more pixels. One of both lengths and widths can be entered to get the other length or width. If length and width are known, then the area in pixels will be calculated.

In the three bottom lines, the number of pixels to be measured can be entered. Clicking *Area* multiplies the number of pixels in width and length.

Example: a map detail scanned with 200 dpi has an original length of 2 cm and width of 1 cm. Digitized it has 157 times 79 pixels, those are 12403 pixels. At a map scale of 1 to 75000, one pixel refers to a size of about 9.5 meters. An area of 500 pixels then has a size of 4.5 hectares. The slightly different values for pixel length and width are due to the fact that there are no fractions of pixels and therefore their number has to be rounded.

A pixel or picture element is a point on the screen. Pixels don't have to be square, but they often are, or at least approximately so. Pixels only occur as whole numbers, there are no fractions of pixels. The larger a single pixel is, the more grainy or "pixelated" the image will appear. More pixels per area make for a better image. Each pixel has a color derived from three values of red, green, and blue. Each of these values often has 256 levels, so that 256^{3}, i.e. 16,777,216 different colors are possible.