Utilizing a JBIG2 Encoder with No Information Loss
The JBIG2 specifications caution against using halftoning since this operation can seriously degrade the image. Similarly, the specs caution against using lossy JBIG2, which can introduce mismatches that degrade document quality, readability, and recognition rates.
The best way to understand such cautions with respect to JBIG2 is that the quality of the JBIG2 encoder is crucial. After all, image thresholding is potentially much more degrading than either font learning or halftoning since the part of the image that needs to be retained, e.g., signature, may disappear entirely. Yet most corporations capture their documents to black and white because they trust that the thresholding function is reliable, and that essential information in the image document will be preserved. They probably also test this assumption before putting their document imaging system into production.
Maintaining Document Integrity with JBIG2
JBIG2 compression can dramatically decrease file size, making documents much easier to transmit over the Web or via email. But a crucial step in maintaining document integrity during the conversion process to JBIG2 (or JBIG2-coded PDF) involves ensuring that the JBIG2 compressor actually enhances document image quality rather than degrades it. As has been shown, this cannot be assumed for all JBIG2 implementations, and results vary widely depending on the JBIG2 coder used.
It is important to understand that effective JBIG2 compression, with compression rates 5x-10x smaller than TIFF G4 (or standard G4-based PDF), cannot be achieved with lossless JBIG2. Moreover, once a lossy JBIG2 encoder is utilized, it becomes essential for the IT manager or project leader responsible for document integrity to ensure that the JBIG2 converter supports perceptually lossless conversion.
The best way to test that a JBIG2 converter is perceptually lossless, i.e., non-degrading, is to visually inspect the image quality of the images before compression and afterwards. As this can be time consuming, it is recommended that instead of manual inspection you do an OCR verification test, which consists of measuring recognition rates both pre-compression and post-compression to verify that there is no loss in OCR recognition accuracy introduced during the JBIG2 compression process.
A crucial step in maintaining document integrity during the conversion process to JBIG2 involves ensuring that the JBIG2 compressor actually enhances document image quality.