This article will review graphic file formats, what makes them different and which one should I choose when saving an image for large format printing?
There are 6 basic file formats that are commonly used to save graphic and image files.
These include JPG, TIFF, EPS, PDF, GIF and PNG. The file compression schemes found in each format offer key features that affect the efficiency, function and even how an image appears.
First let us look at the common compression schemes for these file formats:
- Lossless compression are algorithms that preserve all of the binary information. The most important feature of lossless compresion is when the image is saved, then reopened, there is no loss of image quality.
- Lossy compression algorithms are very efficient in reducing the file size but may compromise the image quality.
Descriptions of the 6 common file extensions:
- JPEG (Joint Photographic Experts Group)— JPEGs efficiently compress images while allowing a choice of quality. JPEG can also be expressed as the three digit extension JPG, depending on the platform. JPEG stores information as 24 bit color. At its highest quality it produces no compression, but the degree of compression is adjustable. JPEGs are useful for archiving flattened images to read-only media. However, when they are opened, altered and saved, they can deteriorate with each saved version.
- TIFF (Tagged Image File Format)—This universal format can be lossless or lossy. Usually TIFFs are saved either without compression or in a lossless scheme called LZW (Lempel Ziv Welsch) that applies limited compression. TIFF is among the best quality output and great when used for large-format printing. A Tiff file will support most of Photoshopʼs features including layers and clipping paths, because of this it is a good format for a work in progress. Tiff format does support RGB color spaces such as CMYK.
- EPS (Encapsulated Postscript)—These files are more or less self-contained, PostScript documents that describe an image or drawing and can be placed within another document generated by a postscript compatible program like Adobe Illustrator or InDesign.
- PDF (Portable Document Format)—PDF is a universal format for document exchange that is used to represent the appearance of a document independent of the software in which it was created regardless, of platform. A PDF file renders a complete description of a fixed-layout, flattened document, including the text, fonts, graphics, pictures and other information needed to display it.
- GIF (Graphics Interchange Format)—GIF images use a color look up table (CLUT) to distill the 16,777,216 colors of the original image into an image containing a maximum of 256 colors. Sometimes GIF applies the closest color in the CLUT to represent each pixel, and sometimes it uses dithering to adjust color of adjacent pixels to better simulate blended colors. GIF format also supports animation. An image with a sequence of layers can be converted to GIF to produce a simple animation for web publications. This is not the best format when to use in large format printing.
- PNG (Portable Network Graphic)—This relatively new format is lossless and maintains quality with limited compression. PNG finds recurring patterns in an image that it can use to compress file size. It uses a lossless two-stage compression scheme known as Deflate. PNG was originally created to improve upon and replace GIF as an image-file format. PNG supports palette-based images with palettes of 24-bit or 32-bit RGB colors and grayscale images. PNG is primarily used as a web format or a screen capture format. This should not be used for large format printing as it does not support non-RGB color spaces such as CMYK.
This information provided in this article is only a guide to understand file formats. Please keep in mind that by changing a file format, will not insert additional data into a given file. The information must reside within the original file to start with.
Practical applications for file formats:
- Print Applications: PDF, Tiff, EPS, JPEG
- Web Applications: PNG, JPEG, GIF
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