Image standards

This is about the nuts and bolts – the technicalities of file types and attributes that will make your images viewable to your readers.

First of all – file formats.
GIF for graphic elements with large blocks of similar colours, for example logos.
JPG for photographs
PNG combines elements of both GIF and JPG

Here is a web site that summarizes the differences and gives some examples.
http://www.sitepoint.com/gif-png-jpg-which-one-to-use/

What if your file is not in the format you want? Most photo editors such as Photoshop can convert your file and save it in multiple formats. Check out this list of free online graphic converters: http://www.internetymultimedia.com/?q=node/58

A word about file size: As a general rule, provide the smallest file size that will meet the quality requirements of your user. For example, a photograph of a work of art that your may need to be examined in great detail will require a larger file size than a photograph that is provided as a general illustration on your site.

Adjusting the resolution (expressed as dots or pixels per inch, or dpi/ppi) can help to achieve this objective. You can do this in Photoshop using the Image Size dialogue box.

 Here is a portion of a photograph that is originally a 180 dpi JPG (175kb)

 This can be reduced to 72 dpi (124kb) without a huge loss of quality:

But if this 72 dpi photo is cropped to show just a small detail, things can get fuzzy!










Remember – once the pixels are gone, they’re gone! Always save your original photos in their highest-quality format and resolution so that you have more pixels at your disposal for future close-ups.