A good understanding of image size is vital to properly utilizing photography. The terminology and even the basics of image file size are confusing if you are not properly trained in digital imaging.
I’m often incorrectly asked for a 300 DPI file. DPI is very often misused as a description of pixel count in a file. PPI (Pixel Per Inch) and DPI (Dots Per Inch) are not the same. The proper term to describe file resolution is PPI. DPI is only used to describe printers. Not only is that request incorrect in terminology but it’s meaningless without a width and height. An appropriate request would be for an 8.5″ x 11″ 300 PPI file.
How big does a file need to be? Not as big as you would think. With the right RIP (Raster Image Processor) there is no difference between a 180 PPI file and a 360 PPI file.
We currently shoot most jobs on a 47 mega-pixel camera. We edit and save the full resolution file in our archive, then deliver a Tiff or JPEG, level 12 files. The file sizes we deliver depend on the kind of images and our client’s needs and capabilities. Headshots are seldom used for anything larger than an 8.5 x 11, so we deliver appropriate files for that use. Architectural photography often needs to be printed at 16 x 20, so we deliver much larger files to architects.
Web images are smaller and they require special sharpening. If we know the images will be used for the web, we size them down to 2000 pixels on the long side and apply the special sharpening. This leaves enough room for cropping and adjusting for placement and any further resizing a client does will not degrade the image sharpness. Web images are best if we can prepare them at the exact size but it’s rare that we are given this info ahead of delivery to the web designers.
Our SmugMug galleries offer clients an excellent way to resize images themselves for their different uses. Please see the SmugMug How To.