Description | Native File Formats | TIFF | EPS | GIF | JPEG | PNG
There are many formats in which images, graphics, and documents are saved. Customers should have the opportunity to select file formats that are best suited to a specific application and are most compatible with a specific production workflow. All file formats have their advantages and disadvantages, so one format doesn't necessarily have to be preferred over another. Described below are several formats, which may help in illustrating how they compare to files saved as PDFs.
Native File Formats
A native file format is one that is the same as the program in which a document or image is created. For example, an image created in a program like Photoshop and saved as a Photoshop file, is an image saved in a native file format.
A problem with native file formats is that if a document is saved in such a format and then it needs to be combined with a document saved in a non-native format, the non-native format may not be compatible with the native format. The native format has to be converted into a format that can be understood by the non-native format.
Most software companies design many of their software programs to be compatible with one another so that documents saved in one program don't have to be converted into a different format so that it can be understood by another program. An example of this is Microsoft Excel and Word, which work well together in their native file formats. An item created in Excel can be brought into Word without any problems.
Even if documents in a native file format are not combined with any other items in different programs, there could still be problems. The native file will still not be viewable on computers that do not have the same software program that the document was created in.
TIFF is an acronym for Tagged Image File Format and is a raster based or bitmapped file format (defined with pixels). TIFF files are very flexible and can be saved as CMYK, RGB or grayscale images in any bit depth or resolution. Almost any graphics program can open and import TIFF files and they can be exchanged between Windows and Macintosh platforms. When you are scanning photographs directly into an image editing program such as Photoshop, the images should be scanned as the program's native file format, otherwise images should be scanned as TIFF.
EPS is an acronym for Encapsulated PostScript. EPS files are usually vector based files meaning that they are based on mathematical formulas to define the characteristics of an image rather than with the use if pixels as with bitmapped (raster) file formats such as TIFF. EPS graphics can be enlarged or reduced without changing the quality of the image and the print quality of an EPS file will be that of the resolution of the printer.
A vector EPS graphic file can be created in a page layout program such as QuarkXpress or PageMaker. The vector EPS document can be opened and modified in a drawing program or it can be imported back into the page layout program onto a different document.
|Note: There are occasions when EPS is used as a format for raster files. For example, a duotone in Photoshop can only be saved as a raster EPS.|
GIF (Graphics Interchange Format) is an image format developed by CompuServe and is the most common type of image format used on the Web. It was developed as a way to store images in small files that can be quickly exchanged and easily downloaded. GIF files have a color depth of 8 bits per pixel. The word pixel is short for picture element, the smallest unit of a digital picture. 8 bits per pixel makes a total of 256 different colors. Because of this, GIF files can be accurately displayed on a greater number of systems, as most systems can display at least 256 colors.
GIF compression is known as a "lossless compression" method, in which the image is analyzed and compressed without the loss of the original picture data. The GIF format is best suited for items like logos, banners, buttons, and graphics, because most of these items are designed with the 256-color palette (8-bit color). If these items are saved as a GIF, none of the original color data will be lost. If the GIF format is used for an image that is larger than 8 bit color, such as a photograph, then the colors in the image that are not found in the 8-bit color palette will be dithered. There is no problem with this except that it creates a much larger file size because there is more information to store due to the number of extra pixels required to create the dithered color.
The compression technique used with GIF is called LZW compression, which stands for Lempel, Ziv, and Welch. These are the mathematicians who were the inventors of this technology. The computer maker Unisys holds the patent on this file compression technique, which means that anyone creating GIF files should owe Unisys a licensing fee for the use of this technology. Most software programs like Adobe Photoshop and Macromedia Fireworks, that are used to create GIF files, are already licensed by Unisys, so most people should not have to worry about it.
Shown below are examples of GIF images.
The JPEG (Joint Photographic Experts Group) format/compression technique was developed specifically for photographs or images that combine artwork and photographs. JPEG is utilized to gain high compression levels for photographic images without sacrificing the image quality. It is used exclusively for the compression of 24-bit images and it will not work for images less than 24-bit. It also does not work very well for non-photographic images such as illustrations, cartoons, flat color areas, or images with defined edges. JPEG is much more suitable for images that contain irregularities and soft edges rather than images with many straight lines and hard edges. The irregularities cause the pixels to be less well defined, which decreases the size of the file. The more irregular an image, the better suited it is for JPEG.
24-bit JPEG images look great on 24-bit monitors, but may not look so good on 8-bit or 16-bit systems. The colors in the 24-bit image that are not contained in the 8-bit or 16-bit palette of the computer system will be dithered. Even if flat areas of color in the JPEG image are among the colors in the 8-bit or 16-bit color palette, there could still be problems with the JPEG image when viewed on a lower bit depth system. The JPEG compression process introduces elements into the solid color areas that make the images look muddy or blurry.
JPEG compression is known as "lossy compression", which means that non-essential data is lost during the compression. JPEG images may be compressed at several levels. The way the compression works is that the image data is separated into levels of importance. The more the image is compressed, the more levels of information are thrown out, which creates a smaller file, and along with it, the loss of image detail. The loss of this data is permanent and it cannot be restored. If the image is not compressed by too great a factor, the overall quality does not suffer that much. With JPEG, you have the choice of compressing an image without sacrificing too much in the way of image quality, or you can have the advantage of having a greatly reduced file size, but a resulting image of much poorer quality.
100% quality = 78.81k
25% quality = 6.73
|Even though the image above has been compressed to 25% of the quality of the original image at the top, the quality of the image above is still tolerable and the file size has been reduced to less than one-tenth of the original size.|
The PNG (Portable Network Graphics) format was developed as an alternative to GIF and JPEG. PNG has several advantages over GIF. It uses a compression technology called deflation, which compresses 5% to 25% better than GIF. It is among the best "lossless compression" types, which are compression techniques in which none of the original data is lost, but the file size is still reduced. PNG supports images with different color bit depths including 8, 16, and 24-bit color, while JPEG supports only 24-bit color and GIF supports only 8-bit color.
Another problem that the PNG format helps to eliminate is brightness or "gamma" differences between monitors. An image generated on a PC may look too light on a Macintosh. An image from a Macintosh may look too dark on a PC and PC created images may not look the same on all PCs. The brightness of a PNG image is automatically corrected to display consistently on different computer monitors regardless of what kind of computer system was used to create the image.
PNG also offers "alpha channels", or masks, which define different levels of transparency. PNG allows up to 254 levels of partial transparency as well as the ability to be fully transparent of fully opaque. GIF supports only binary transparency (a pixel can be either fully transparent or fully opaque). Alpha channels allow images to be created with faded edges such as a vignette, where a subject at the center of an image can be fully opaque and then gradually fades out to the edges where it can be fully transparent.
Consider using the PNG format over other formats in the following situations:
- Use PNG if you have an image with multiple levels of transparency.
- Images containing line art or text can be saved as a PNG image.
- PNG is a good choice for color images that you want saved in a lossless format.
- Use PNG for images that contain large areas of flat color.
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