JPG, GIF, TIFF, PNG, BMP. Many
file formats are used to for digital images. It can be confusing, but the choosing is not difficult.
A big reason that so many file formats exists is the need for compressing, or making the files smaller for Internet downloads, emailing, or diplaying the files. With modern digital cameras the image files can be quite large. Larger files mean more disk usage and
slower downloads. "Compression" is a term used to describe ways of reducing file sizes with minimal impact on the final look of the file.
Another factor that impacts the file format selection is the number of colors contained in the image. A logo file with crisp lines will have fewer colors than a picture with many shades of the same color.
TIFF is a very flexible format that can be lossless or
lossy based upon what you tell your editing program. The details of the storage algorithm are included as part of the
file. TIFF is exclusively as a lossless image storage
format that uses no compression at all and is compatible with a variety of editors. TIFF file sizes are larger than other file types.
Summary: TIFF means better quality. However, the file
size is huge compared to even the best JPG setting, and the advantages may not
be noticeable. Use it as a "working" file format when you may be sharing it with people with other editing software.
PNG is also lossless and is growing in popularity. As opposed to the
TIFF format PNG will take advantage of patterns in the image which can be used to compress the file. The compression is 100% reversible, so the image is not altered.
Summary: PNG is superior to GIF. It produces smaller files and reproduces
more colors. PNG also supports partial transparency. Partial transparency
can be used for many useful purposes, such as fades and antialiasing of text.
Use PNG when an image with large areas of exactly uniform color and contains
more than 256 colors.
GIF creates a table of up to 256 colors from the pool of 16 million. If
an image has fewer than 256 colors, GIF can render the image exactly. When
the image contains many colors, software that creates GIF files will use one of several
algorithms to approximate the colors in the image with the limited palette of
256 colors. The best algorithms will search an image to find an optimum
set of 256 colors. Sometimes the nearest color will be used to represent each pixel,
and sometimes a process called "error diffusion" will be used to adjust the color of nearby
pixels to correct for the error in each pixel.
GIF achieves compression, or smaller file sizes, in two ways. First, by reducing the number of colors
of color-rich images which reduces the amount of data stored about the image and secondly it replaces commonly occurring patterns. This is why this format works so well for logs and drawings.
Summary: Do NOT use GIF for photographic images, since it can contain only 256 colors
per image.
JPG is optimized for photographs and images with a wide range of colors that contain many, many colors. JPG can achieve great compression ratios
while maintaining great image quality for the intended use. JPG works by discarding picture information
that the eye is least likely to notice. The information stored is 24 bit color.
One beauty of JPG is that the degree of compression is adjustable. At moderate compression
levels of photographic images, it is very difficult for the eye to tell that the image has changed. Compression factors
of more than 25 are often quite acceptable. Better graphics programs, such as
Paint Shop Pro and Photoshop, allow you to view the image quality and file size
as a function of compression level, so that you can choose the
balance between quality and file size.
JPG is the most common format for nearly all photographs on the web. It will render excellent quality at higher compression settings. When editing, use your software's proprietary format until finished, and then save a copy in the JPG format.
Digital cameras typically save in a JPG format by default.
Summary: JPG is an excellent format for digital photographers to store their final image and to reduce the size of their image for emails and web posting.
RAW is an image output option available on many medium quality to professional digital cameras. The beauty of a RAW file format is that it allows you to have more ability to edit the images than other formats. The disadvantage is that there is a different RAW format for each manufacturer,
and so you may have to use the manufacturer's software to view the images.
(Some graphics applications can read some manufacturer's RAW formats.)
BMP is an uncompressed proprietary format invented by Microsoft. Don't use it.
PSD, PSP, etc., are formats used by graphics programs.
Photoshop's files have the PSD extension, while Paint Shop Pro files use PSP.
These are the preferred working formats as you edit images in the software. If you are planning to share these files save them into a TIFF format.
GIF, PNG, and JPG are the formats used for nearly all web images. PNG
has only recently became widely supported so most of the web images are one of the other two formats.
