Now to complete the series on CCITT, I will go as in-depth on how to decode a G31D encoded PDF file. G31D CCITT is a variation to the Huffman keyed compression scheme. Essentially to decode a G31D PDF file, a scan line is read in single bit pixel runs. Each of these bits representing a…
In my second article on CCITT encoding I am going to explain exactly how 1D decoding works. Just to make life complicated, this can have several names. I will be referring to the Group 3 One-Dimensional as G31D. This has also been referred to as 1D CCITT in our office (why complicate things ey..?). A PDF…
As part of the rewrite of our Java CCITT Decoder, I have spent a lot of time with the format. It is quite a complicated topic so I thought some articles would be helpful. There are actually several types of CCITT. When decoding CCITT encoded PDF files there are three different types of CCITT formats…
While rewriting our CCITT decoder (almost finished!) we came across an interesting item to take care of. When reading the values of a CCITT encoded data stream, you need to be careful with the values you read in. In general, the CCITT dictionary can contain a /Rows value which is actually the height of the…
CCITT encodes black and white data. It does this by encoding runs of black or white pixels. This data can be stored using one bit (0 or 1), so which do we use for black? As most images contain more white than black, we assume that we start with white. For cases where we do…
