As digital cameras continue to increase in the amount of data they can capture, reducing file size during image editing becomes an important issue. Photographic files can easily reach sizes of several megabytes of information which takes a long time to email, even over a high-speed connection. Images of this size also take long periods of time to view if posted on the Internet.
To manage image size during photo editing, you must take into account the major contributors to file size. These are image complexity, resolution, and compression.
Image complexity is an often overlooked factor in reducing file sizes...especially when resizing photos. As shown in the example photo, the more complex the subject - the larger the file size. This is because there is more information contained in the complex image of the flowers when compared with the relatively simple image of the fireworks. When posting images on the Internet or emailing photos, 50K is a good "rule of thumb" for a target file size.
Photo resolution is another major factor to consider in managing file sizes and resizing photos during photo editing. Resolution is more than the Megapixel rating of your camera (that affect image complexity). Resolution is the dots per inch (DPI) or pixels per inch (PPI) at which the image is printed/displayed. An 8x10 image displayed at 72ppi will have a much smaller file size than an 8x10 image displayed at 300ppi. When posting images on the Internet or emailing photos, 72dpi is sufficient as this is the "native" resolution of monitors. When printing images, 300dpi or more is preferred to create a quality image.
Compression is a fancy computer term for packing as much data as possible into a small space. Compression relies on a computer program "re-inventing" some of the data originally present in a photograph to recreate the image when opened by another computer. This method can reduce file sizes greatly during photo editing but data is lost and image quality is negatively impacted. Compression should be a last choice when attempting to manage file sizes during image editing.