The Attribute Lossy Image Compression (0028,2110) conveys that the Image has undergone lossy compression. It provides a means to record that the Image has been compressed (at a point in its lifetime) with a lossy algorithm and changes have been introduced into the pixel data. Once the value has been set to “01”, it shall not be reset.
Note: If an image is compressed with a lossy algorithm, the attribute Lossy Image Compression (0028,2110) is set to “01”. Subsequently, if the image is decompressed and transferred in uncompressed format, this attribute value remains “01”.
The value of the Lossy Image Compression (0028,2110) Attribute in SOP Instances containing multiple frames in which one or more of the frames have undergone lossy compression shall be “01”.
Note: It is recommended that the applicable frames be noted in the Attribute Derivation Description (0008,2111).
If an image is originally obtained as a lossy compressed image from the sensor, then Lossy Image Compression (0028,2110) is set to “01” and Value 1 of the Attribute Image Type (0008,0008) shall be set to ORIGINAL.
If an image is a compressed version of another image, Lossy Image Compression (0028,2110) is set to “01”, Value 1 of the Attribute Image Type (0008,0008) shall be set to DERIVED, and if the predecessor was a DICOM image, then the Image shall receive a new SOP Instance UID.
Note: 1. It is recommended that the approximate compression ratio be provided in the Attribute Derivation Description (0008,2111). Furthermore, it is recommended that Derivation Description (0008,2111) be used to indicate when pixel data changes might affect professional interpretation. (see C.184.108.40.206.3).
2. The attribute Lossy Image Compression (0028,2110) is defined as Type 3 for backward compatibility with existing IODs. It is expected to be required (i.e., defined as Type 1C) for new Image IODs and for existing IODs that undergo a major revision (e.g. a new IOD is specified).
The Defined Terms for Lossy Image Compression Method (0028,2114) are:
ISO_10918_1 = JPEG Lossy Compression
ISO_14495_1 = JPEG-LS Near-lossless Compression
ISO_15444_1 = JPEG 2000 Irreversible Compression
ISO_13818_2 = MPEG2 Compression