File Type and File Compression Printing Knowledge
File Type and File Compression

Digital cameras save images as a file format so they can be recorded electronically in some form that allows for storage, exporting and re-purposing of the image. Before selecting a camera, consider the final use of the image (print publishing, Web publishing, digital presentations, etc.) to insure that the camera supports a format fitting the purpose of the required use of the image or image output.

There are several different formats or file types that enable the images to be used for various purposes, such as insertion into Web pages, transfer to remote locations, or output to high-resolution proofs and final copies. A specific format may be selected because it compresses the file into a smaller size (lower resolution) so it can be handled more effectively in the camera's memory. Or, a lower resolution format may be used because the image will be used for Web work, which does not require higher resolution.

The purpose of compression formats created by digital cameras is to reduce the size of the image file in order to allow more images to be placed into the camera's internal memory or onto removable media storage cards.

  • Compression ratios are used to calibrate different image file sizes, such as 1:2, 1:4, 1:7, 1:12, etc. As the ratio increases the quality of the image decreases, causing artifacting, or degradation of the image. A compression of 1:4 will provide a sharp image with no loss of quality. The size of the compressed image will change according to the subject within the image. Fine detail or a wide range of depth, such as tree branches and leaves, creates a much larger compressed image than expanses of plain colored backgrounds, such as sides of plain buildings.
  • Most cameras have settings that are used to select the level of compression (the compression ratio) for the image. Settings may be designated as good, better, fine, best, or low, medium, and high. The "best" or "low" setting allows the least amount of compression and the best quality image.
  • Fixed resolution cameras increase the compression of the images as more images are taken and placed in the camera's storage. The compression process decreases the quality of the image, since the image compression increases as additional pictures are added to the stored images.
  • Some cameras will begin by slightly reducing the resolution in order to keep compression at a minimal level. This alternate process provides a smaller image file and improved overall quality.
  • When saving images in a format such as JPEG or FlashPix, the camera automatically selects the setting and compresses the image.

 
There are two types of compression, "lossy" and "lossless", both of which are used in digital cameras.

  • Lossy compression is used for JPEG files. The notable characteristic is the loss of quality the more the image is compressed. The algorithm "looses" data in order to create a smaller file size. The loss of data is most noticeable when the image is output in larger sized copies.
  • Lossless compression is used most often in the professional level cameras. A lossless compression format, such as TIFF or GIF, will not change the quality or image details once it becomes a file. (GIF is a file format that is used primarily to display line art on the Web and is not used by digital cameras.) Therefore, the quality of the compressed image and decompressed image most often will match the original image. Generally, a camera with lossless compression is connected directly to a computer hard drive.

 
When transferring the image to another computer or storage device, the format must be able to be read and supported by the program on the receiving device. However, regardless of the camera's file format, once it is downloaded to a computer, it can most often be reconverted to another format that may be required for use in the computer program that will contain the image. Some of the following formats are currently being offered in the digital cameras:

  • Raw Image Format:  To preserve image quality, some cameras will record a raw image (also called CDD raw image) as an uncompressed file or uninterpolated data on the camera's sensor where the pixels are built for the final file. The uncompressed file format is not as common as TIFF or JPEG and may provide some difficulty for use with computer programs that alter or re-purpose the images if they are in a common format.
  • Proprietary Formats:  Some cameras use a format that has been developed by camera manufacturers in order to attempt to create a competitive advantage. The format developed by the manufacturer may actually cause some problems for the user since they will be required to make sure the format is compatible with any software into which the image is being imported for use. Several types of proprietary formats are EXIF, which is supported by Kodak and Fuji, and CIFF, which is supported by Canon, Nikon, Pentax, and several others.
  • JPEG:  JPEG is the most common compression format used by camera makers because it is easily compressed and it is also the most common method of presenting images on the Web. It is used exclusively for the compression of 24-bit images and it will not work for images less than 24-bit. Cameras are often equipped with compression selections allowing the file to be saved in one of three levels of JPEG compression. If the image is to be edited once it is downloaded to a computer, don't save it as a JPEG, but instead save it in a loss-free format such as TIFF. JPEG files decrease in quality as they are saved, opened, and saved again, because each time the image is compressed, quality is decreased.
  • TIFF:  TIFF (Tagged Image File Format) is the most common format for saving bitmapped images that will be printed or imported into a page layout program such as QuarkXpress or PhotoShop. A TIFF file can be CMYK, RGB, grayscale, index, or bitmap. TIFF will support up to 24-bit color.
  • FlashPix:  Developed in 1995 by Kodak, Microsoft, HO, and LivePicture, this image format allows you to save images in several different resolutions. It supports multi-resolution images, continual downloads without loss of quality, and the use of metadata.
  • MPEG:  MPEG (Motion Pictures Expert Group) is a format used to compress audio and video images. Although the quality of MPEG is not currently as good as DVD or VHS, efforts are being undertaken to improve the clarity and sharpness, which should be possible in the years ahead. Several of the still cameras are using the MPEG format to capture short audio and video clips. MPEG-2 is currently being developed as a higher quality format for use in video imaging.

 


 

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