Publishing Digital Photos

Introduction

Publishing brings into play a whole array of issues, most of which come down to a basic conflict: file size vs. image quality. In the printing world, file size is rarely a concern - when an image is to be printed on paper, the greatest possible image quality is the only priority. However, as this is a course on digital photography for web multimedia, file size becomes an important consideration, since it translates to the amount of time it takes for your audience to download your content.

Consider your target audience. Will your pictures be seen by university students surfing from a lab with a T-1 connection, or your family members who still connect at 28.8? Regardless, a good rule of thumb is that faster is usually better - people adore software upgrades that make their web browsing experience more snappy, but few web designers acknowledge that they have the power to improve the speed of their own sites by merely optimizing their content.

Optimization means web files that are sized appropriately for the content they deliver. With html files, one must remove unnecessary clutter from one's code, making the file size as small as possible while still producing the exact same arrangement of text and graphics on the page. With images, the principle is similar in that one must make file sizes as small as possible while still delivering an arrangement of tiny colored dots which form a picture that is pleasing to the eye.

Image size

Image size can be expressed either in inches or in pixels: it is the exact width and height of the image. Usually, pixels are a better unit for digital pictures, since they give a more precise measurement. Image size could be considered a relative measurement, as image resolution can vary; but since the web world is most often a medium viewed from a computer monitor and not printed on paper, image resolution will have a constant number as a point of reference (see below, Resolution).

As one would imagine, the larger the image size, the better the quality but also the larger the file size. Image size is the first factor of an image's quality to consider, when optimizing it for the web: the photographer must decide how small the image can be without a loss of quality.

Resolution

Like image size, resolution is another way to increase image quality, since higher resolution means more dots of color, more information to represent an image and a likelyhood for more detail and clarity. At least this is true for acquiring an image (i.e. with a scanner), or printing it on paper. However, computer monitors are only capable of displaying at 72 dpi (dots per inch), so an image resolution of 300 dpi merely means it will be displayed larger on the screen to compensate. In web publishing, this translates to an image that appears larger than intended and takes up several times more disk space. Anyway, digital cameras usually capture images at the same resolution as the monitor will display, the humble 72 dpi.

Compression

The third factor to affect an image's quality is the level of compression. An uncompressed image is one whose file format contains the exact color information of every dot in the image, in order as the dots appear; an uncompressed image thus could be said to have the maximum file size for a particular file format. Compression is a way of analyzing the image for repeating colors, repeating patterns, which can be represented by a shorter amount of code in the file format. Compression can decrease the file size even further by making compromises in the dot information, modifying the image's appearance to a degree that may or may not be detectable by the eye. The amount of compression that can be applied without a visible loss of quality depends largely on the complexity of a particular photo; thus it is finally up to the eye of the photographer to decide on the maximum amount of compression that will still produce an acceptable image.

The guy at the computer on the other end

Remember that your audience is affected to some degree by the choices you make in your finished images. The larger they are, the longer they take to download. The guy on the other end can become impatient if your image takes a long time to transfer compared to the benefit he expects from seeing it. He may have a slower internet connection than you do. He may have an email ISP that caps his account at a lower amount of space, so the large images you send may fill it up too fast. Basically my advice is don't waste space - optimize your images for the effect you wish to deliver. If an image looks the same (or close enough) with more compression, and has an acceptable amount of detail with a lower image size, it means your audience gets essentially the same picture, but faster.