Get your head around image file types
From jpg’s to tif’s to bmp’s there are many file types that can be utilized when optimizing images for the web or preparing hi-res photographs for printed materials. Every situation is different, but a few general rules apply. Here I will provide an overview of the three most common files types and the best applications for them.
The most common image file format is the JPG or JPEG (developed by Joint Photographic Experts Group). I believe that this is because a JPG is a compressed file with reasonable resolution output and is easily recognizable by the most common software types. It is therefore a format that you will generally receive or send via email when mailing to a recipient. When exporting an image as a JPG from image editing software, there are generally several options, the most common being “quality”. This is usually represented by a percentage value or high – low resolution scale. As a rule of thumb, a high resolution or 100% quality rated file will create a larger file size than those of lower resolution or 10% for example.
I like using Macromedia Fireworks for editing these types of images as you can preview the quality of the file verses size before the image is exported. This is particularly useful when preparing images for the web where small file sizes and lower resolution files are more acceptable. The disadvantage with using JPG images is that resizing of the image after converting to JPG will produce a very low quality file. The more times you adjust and output the file, the quality further worsens, so be sure to keep a back up of your images. The compression agent used for JPG conversion compresses the file by removing redundant pixels from the image, by this I mean that pixels of repetitive (or similar) color variations are removed and grouped together to use less colors and reduce the memory taken to store the file.
JPG’s may also be used for printed pieces where image quality is not essential, this will help keep the file size of the materials lower and aid electronic distribution in PDF (Portable Document Format) for example.
JPG image with low compression
JPG image with high compression
GIF (Graphic Interchange Format) was developed by Compuserve and is probably the second most common format used for the web because of its low file size and readability by all browsers and desktop computers. The GIF compression agent works similarly to JPG compressors in that the number of colors are reduced to save on memory. The GIF file format allows a maximum of 256 web-based colors which helps keep the file size low. Most export software applications allow you to set a specific color range (number of colors) to further reduce the file size. The software will automatically substitute any colors in the image that does not fall into that color range with the closest match. You may have to experiment with color ranges to find the optimal file size vs. image quality combination. So, if you have an image with few colors such as a company logo, the GIF file format is the best method for optimizing your file for the web. However, if the image contains many colors, JPG compression maybe a more suitable alternative to maintain the best quality of the image while maintaining a low file size. One distinct advantage of the GIF file format over JPG is that the “transparency” of your image can be preserved. For example, if a company logo is to be placed on a web page with a specific colored background you will want to preserve the transparency of the image while exporting. Otherwise, the image will appear on the web page with a white background.
GIF logo without transparent background
GIF logo with transparent background
TIF (Tagged Image Format) files will consume the most memory of the three file types discussed here. At the same time a TIF file will provide the best quality image, capable of very hi resolution output in excess of 1000dpi (dots per inch). A TIF file is an ideal option for incorporating into printed pieces as the image quality is sufficient and can be provided in CMYK.
A downfall to TIF format is that, although your images can be exported with transparency and layering preserved, very few page layout applications have the ability to read TIF files exported this way. This is particularly important when creating an image for import into a advertisement, brochure etc. where the background has to be visible around the immediate edge of the image. In such a case an EPS (Encapsulated Post Script) file should be used. As a quick note on EPS files, these enable you to maintain quality, color matching and transparency when exporting for use in a different application, however, these files can become very large and memory intensive.
I trust that this overview on some of the most common file types used for web and print applications has been informative and valuable for you when preparing either printed materials or for web-based applications. Feel free to drop me an email with any image preparation questions that you may have.
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