uncmpJPG is the name of the special core JPEG codec used in packJPG v2.4. Compared to other JPEG codecs the main difference is that this codec performs decompression and recompression without introducing any further loss – a JPEG file that goes in it is bytewise identical to the JPEG file that goes out. As such, this codec is well suited to be used as a starting point in lossless JPEG recompression projects. There are some rare cases in which a JPEG file can’t be processed losslessly. In these cases uncmpJPG will display a error message.
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uncmpJPG v2.4 (BSD)
uncmpJPG accepts JPEG and UJG (Uncompressed JpeG) files as input – JPEG are converted to UJG and vice versa. An UJG file consists of all information needed to losslessly reconstruct the original JPEG file. Contained are JFIF file header, decompressed DCT coefficients and, if needed, some special file reconstruction information.
Please note that uncmpJPG is based on packJPG v2.4, while the most recent version (on Feb. 23., 2014) of packJPG is v2.5i. Therefore may not work as comaptible and reliable for you as packJPG does.
You may freely use uncmpJPG and it’s source code under the terms of the BSD. uncmpJPG is also included in the JPEG Open Source Developers Package.