We are wondering why there is no “Retain” option for CompressionMode for Monochrome images, whereas there is one for Grayscale and Color images.
A:
PDF supports many different monochrome image compression types which PDFNet supports as a consumer. However, there are a number of monochrome compression methods we do not support for writing (because they are less optimal than JBIG2) so having a retain option would not be very accurate. In almost all cases the optimal behavior is to compress monochrome images that need to changed with JBIG2 compression.
Just to clarify, are you saying that to retain the existing compression type, PDFNet needs to support writing that compression type because it actually re-compresses the stream, rather than leaving it exactly as-is? Is that only the case when downsampling is enabled?
A:
Unless the ForceRecompress option is turned on PDF Optimizer will not automatically recompress images, but downsampled images must be recompressed. So if downsampling were to be disabled and ForceRecompress was off no recompression would occur.
On Thursday, March 8, 2012 2:34:09 PM UTC-8, Support wrote:
Q:
We are wondering why there is no “Retain” option for CompressionMode for Monochrome images, whereas there is one for Grayscale and Color images.
A:
PDF supports many different monochrome image compression types which PDFNet supports as a consumer. However, there are a number of monochrome compression methods we do not support for writing (because they are less optimal than JBIG2) so having a retain option would not be very accurate. In almost all cases the optimal behavior is to compress monochrome images that need to changed with JBIG2 compression.