Digital images are made up of many thousands or even millions of tiny squares (or rectangles) called picture elements or pixels. Each pixel represents an area of the image produced by the microscope and its intensity is linearly dependent on the charges generated by the incident photons in the corresponding photodiode of the parallel shift array of the CCD chip. The more pixels there are in a given image area the higher the resolution of the image. If a digital image is increasingly enlarged there will come a point when the individual elements can be seen as separate dots – similar to graining in silver halide photography – and the more pixels an image contains per area, the more it can be enlarged before the separate pixels start to show. The size of the image can be described by its dimensions in numbers of pixels, for example, 1280 x 1024 pixels. Especially digital consumer cameras are often specified by the total amount of pixels their images consist of, in the case above it would be 1.31 million (= 1.28 megapixels).



Zooming in the details of a digital image reveals its composition of many square pixels:




The examples below show how pixel size, that is, number of pixels per image area, directly influences resolution.
The resolution loss in the first images is the same as would result from 4x4 binning.