# Supported File Formats

ZEHRaster Plus supports the following file types:

- TIFF
- JPEG
- CALS Type 1 CCITT Group 4
- CGM*

## Raster File Information

Raster files, like TIFF, JPEG and CALS, are created by many graphics applications.

A raster file uses pixels of color to approximate the image you see. A raster file will have a resolution of pixels per inch (ppi) that refer to how many pixels of color are used per square inch. These pixels per inch in the file are mapped to the dots per inch produced by the printer. Generally, the more dots per inch used by the printer, the smoother the colors appear on the output image (e.g., a 600 dpi printer can provide a much "cleaner" looking print than a 300 dpi printer). However, image/print size and resolution affect each other.

## Resolution and Image Size

A raster file has a "resolution" measured in pixels per inch. It gets this resolution from the resolution at which the original image was scanned or created.

For example, let's say an application creates a TIFF with a resolution of 600 pixels per inch (ppi).

If you print this image on a 600 dpi printer, it will be produced at approximately the same physical size as the original scanned image. If you print this image on a 300 dpi printer, it will be produced at approximately twice the size of the original. Likewise, if you print this image on a 1200 dpi printer, it will be produced at approximately half the size of the original.

Please keep in mind that an image created at 300 ppi and printed at 600 dpi will not produce as attractive output as if the image had been created at 600 ppi. Generally, the more pixels you have to work with, the better the output, whether the output is the TIFF itself or a printed image.

Note that a TIFF as displayed in the ZEHRaster Plus submittal tools Preview window is not actual size. The Preview window's purpose is only to help you determine that you have selected the file you want to print; it should not be used to determine the output size of the image.

## What Makes CGM Different?

One important difference between CGM and raster is that CGM is primarily a vector file format (though it can contain raster data).

A vector file uses the Cartesian coordinate system to describe the primitives (shapes) that make up the image, such as lines, polygons, arcs, and circles. This geometric description allows the image to remain smooth whether the user zooms in on the image in a CGM viewer or prints the file at ten times its original size.

As mentioned above, a raster file uses pixels of color to approximate the image you see. A raster file will have a resolution of pixels per inch (ppi) that refer to how many pixels of color are used per square inch.

To better understand the difference between these two types of files, let's say a CGM and a raster contain an identical image: a circle .5 inches in diameter is drawn in black on a white background.

When the CGM is printed, the circle will remain smooth regardless of how much the file is enlarged or reduced.

Original Image | Enlarged Image

When the raster is printed, the more the file is enlarged, the more pixels are distinguishable. Why? The tiny dots appear smooth and create an unbroken line when the file is printed at its normal size. But enlarging the file causes each dot to be enlarged, making those dots appear more distinct.

Original Image | Enlarged Image

Support for the CGM format is available as a licensable option. To license ZEHRaster Plus CGM viewing and printing capabilities, visit our website at http://www.zeh.com/zplus/.