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The Scan Manager lets you select levels of PDF Compression to find a good balance between good image quality and small file size when exporting to a PDF file. This setting would remain in effect until you change it.
The menu looks like:
Note that the "active" compression method has the check mark.
The valid options for PDF compression are:
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No Compression - the file is not compressed. This will be the highest quality, but also the largest file size.
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RLE Compression - Run length encoding (RLE) is perhaps the simplest compression technique in common use. RLE algorithms are lossless, and work by searching for runs of bits, bytes, or pixels of the same value, and encoding the length and value of the run. As such, RLE achieves best results with images containing large areas of contiguous colour, and especially monochrome images. Complex colour images, such as photographs, do not compress well – in some cases, RLE can actually increase the file size.
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GROUP3 Compression - Officially known as CCITT T.4, Group 3 is a compression algorithm developed by the International Telegraph and Telephone Consultative Committee in 1985 for encoding and compressing 1-bit (monochrome) image data. Its primary use has been in fax transmission, and it is optimised for scanned printed or handwritten documents. Group 3 is a lossless algorithm, of which two forms exist: one-dimensional (which is a modified version of Huffman encoding) and two-dimensional, which offers superior compression rates. Due to its origin as a data transmission protocol, Group 3 encoding incorporates error detection codes.
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GROUP4 Compression - Group 4 compression, officially CCITT T.6, is a development of the two-dimensional Group 3 standard, which is faster and offers compression rates which are typically double those of Group 3. Like Group 3, it is lossless and designed for 1-bit images. However, being designed as a storage rather than transmission format, it does not incorporate the error detection and correction functions of Group 3 compression.
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JPEG Compression - The JPEG compression algorithm has its origins in moves to develop compression techniques for the transmission of colour and greyscale images. It was developed in 1990 by the Joint Photographic Experts Group of the International Standards Organisation (ISO) and CCITT. JPEG is a lossy technique which provides best compression rates with complex 24-bit (True Colour) images. It achieves its effect by discarding image data which is imperceptible to the human eye, using a technique called Discrete Cosine Transform (DCT). It then applies Huffman encoding to achieve further compression.
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