Question: What is the difference between lossy and lossless compression ? How can I be sure that the converted documents look the same as the originals?

Answer: Lossless compression does not change any of the original pixel values as captured by the scanning or MFP device. Lossless color JPEG is easily 10x-100x larger than standard JPEG. In fact, no hospital we’re aware of stores its brain MRIs and CAT scans using a lossless format (such as lossless JPEG). For all real applications, certainly in the greyscale and color domains, some modification of original pixel values is accepted. The general rule is that compression and dpi reduction are allowed separately, or in conjunction, as long as the output image appears identical to the original. So this condition of “appears identical” seems to be key. Clearly, appearing identical is also a function of the device, application, practitioner, and other factors.

With perceptually lossless compression, pixel values are allowed to change provided the output image looks like the input image. With perceptually lossless compression, there should be no loss in readability. With effective perceptually lossless compression, recognition rates after compression should be identical to recognition rates before compression.

Checking the documents manually is still the best way to be sure there are no differences between the original files and the converted ones. CVISION ICert is an automated accuracy checking system to verify that each output file accurately corresponds to its input file.