About file sizes

Digital cameras provide file sizes that are measured in pixels.

The file size from a professional camera with a full frame sensor is typically around 5600 x 3740 pixels (= 21 megapixels) – this we call a camera file and the uncompressed file size is around 20 MB.

We provide our customers with more manageable file sizes.

But first an explanation of dpi

dpi (dots per inch) is simply the resolution at which the files are used – the term in fact should be “pixels per inch”(ppi) because “dots per inch”actually refers to print quality i.e. the number of dots of ink per inch. When viewing on a screen (computer or TV) you are actually looking at pixels.

So the higher the resolution (measured in ppi or dpi) the larger is the file size.

Professional photo labs print at 300 dpi – so if you divide 5600 pixels by 300 you get a print that is 18 inches wide. Magazines are also printed at around 300 dpi.

Inkjet printers (like the one in your home or office) print at 150 dpi and newspapers are printed at around 120 dpi.

Screen resolution is actually 72 ppi (not dpi)

So a photo file is just X pixels wide by Y pixels high. Then the software that they are viewed in or printed via will determine what dpi or ppi is used.

We supply to our clients large and small size files.

Large files are 3600 x 2400 pixels and are compressed to 90% to give you a file size of around 2 MB.

So divide 3600 by 300 and you get a professional print that is 12 x 8 inch (close enough to A4) or divide by 150 and you can print on your inkjet printer to 24 x 16 inch.

We also supply small files at 1280 x 850 pixels compressed to 80% (file size around 500 Kb).

These files are designed for web use and usually have to be reduced even further in size for that.  The typical large size on Facebook for example is 640 pixels wide. To put this in perspective a typical (new) widescreen 20” flat panel monitor is 1920 x 1200 pixels.

Do the sums again and divide by 150 and you have a file (1280 x 850 pixels) that will print at 8.5 x 5.7 inches (close enough to A5) on your inkjet printer.

So now lets take our small file (1280 x 850 px) and view that on a 72 ppi screen – the image will now be 18 inches wide.

We edit at full camera resolution and keep those files on file – so if you have any need of the files for large posters or a billboard, we can supply those files.