Types of Image Compression for Medical Imaging

Regardless, the lossy compression algorithm can compress the image at a much higher rate than that achieved by lossless compression, ensuring a faster transfer rate and a smaller storage space. However, because some data is permanently lost, errors can occur during the restore process, so it is not guaranteed that the regenerated image is an exact copy of the original image. Typical compression ratios achieved can be between 5 and 50. Lossy data compression is generally acceptable, but playing with medical images is not that easy.

Image compression is the process of obtaining a compact representation of an image while maintaining all the necessary information important for medical diagnosis. The purpose of image compression is to reduce the image size in bytes without affecting image quality. Reducing the image size saves space for storing images. Image compression methods are generally categorized into two central types: lossless and lossy methods. The main purpose of each type is to reconstruct the original image from the compressed original image without affecting the numerical value or the physical value.

There are two types of compression: lossless and lossy. For lossless compression, the original image can be reconstructed from the compressed image, since no information is lost during compression. This is not true for lossy compression. With lossy compression, loss of data can not be restored. The lossy compression algorithm always has a better compression ratio (the ratio of the size of the compressed image to the original image) than lossless compression. However, this compression rate sacrifices quality and becomes more evident after the image is magnified. This significant degradation in quality or image distortion is called compression artifacts.

There are two basic types of image file compression. Lossless file compression reduces the size of the image file while preserving the integrity of the image data. An example of lossless file compression is a compressed TIFF file format that uses the Lempel-Ziv-Welch (LZW) algorithm. Compressed TIFF files are not generally supported by imaging software, but this type of file compression is suitable for scientific data. Another more common type of image file compression is lossy file compression provided by JPEG and other file formats. JPEG is an ISO / ITU 13 standard file format for storing images compressed by discrete cosine transformation (Microsoft Corporation 1997). JPEG file format does not apply to scientific data images due to image data change. The discrete cosine transform changes the spatial resolution of an image and the intensity of any pixel (Russ 2004)

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