File Format

[Sunite]

File Format
 

For saving local copies of your scanned images you have many choices of file format. The Windows Bitmap (BMP) format is widely used, particularly by people using the Windows operating system. Perhaps the most widely recognized file format is Tagged Image File Format (TIF). Unless you have a specific reason to use another format I doubt you can go wrong using BMP or TIF. The resulting files are relatively large but unless you are scanning a large number of stamps this should not be a problem.

 
For Web publishing your choices are much more restricted. At present there are only two graphics file formats with wide support on the Internet: Graphical Interchange Format (GIF) and Joint Photographic Expert Group (JPG) format. GIF format can be used only with 256 color and gray scale images. Since many stamps, particularly older ones, were printed in a limited range of colors, the GIF format is perfectly adequate. When the purpose of an image is to show the stamp's centering and perforations, GIF will always serve perfectly well. Its advantage over the JPG format (discussed next) is that the file size is often smaller. GIF files are compressed to save space using a loss-free compression scheme, which means that the image you get out is exactly the same as the image you put in.

How can a GIF file, with only 256 colors, give decent reproduction? Here's how it works. When you save a file in GIF format, the software analyzes the image and selects the 256 colors, from some 16 million that are available, that the image will use (this is called the palette). For example, with a stamp that uses shades of red on a white background, the palette will consist entirely of shades of white and red - enough different shades to give an excellent reproduction.

For True Color images you must use JPG. A True Color image can display over 16 million different colors. For accurate reproduction of stamps with many colors, such as those that use photographs, JPG is required. The JPG format introduces one additional complication. Like GIF, JPG is a compressed format. Unlike GIF, JPG uses a lossy compression algorithm which means that some information is lost during compression - in other words, the image you get out is not as good as the image you put in. When you save an image as a JPG file you must specify the level of compression to use. More compression results in a smaller file and lower image quality.