PDF Optimizer

Monochrome

downsample Ability to specify a target resolution and a trigger resolution at which monochrome images will be recompressed.
trigger-dpi All monochrome images above this resolution will be resampled.
target-dpi The new resolution of resampled monochrome images.
recompress Sets the type and quality of compression used to resample monochrome images. Jpeg compression is a compression format used for rendering photographs as image files. It is also known as dct, Discrete Cosine Transform.

JBIG2 is a compression algorithm designed for binary images, or images where each pixel can only have one of two possible colors. For PDF Optimizer JBIG2 is used for black and white images. It can be used for either lossy or lossless image processing.

CCITT Group 4 refers to the compression type from the International Telegraph and Telephone Consultative Committee (CCITT),or TIU. Many fax and document imaging file formats support this form of lossless data compression encoding. These protocols are referred to as CCITT Group 3 and Group 4 compression, respectively.

Lossy and lossless refer to the approach used for compressing data. For lossless, all of the data in the image is preserved. The quality of the image does not change, and it can be uncompressed to its original state. Lossy compression permanently removes data from the image file, such as pixels, reducing the image resolution. Files reduced using lossy compression will be considerably smaller, but will not print or display as well as those compressed using lossless compression.

type same Keep original default compression algorithm provided in the images themselves
jbig2 Use jbig2 compression
ccittg3 Use ccittg3 compression
ccittg4 Use ccittg4 compression
quantity lossy Valid for jbig2 only
lossless Valid for jbig2 only

Optional. Enable any of these values by adding it to the profile and setting it equal to ON.

optimize-images-only-if-reduction-in-size Set this value to ON if you want PDF Optimizer to only downsample an image found in a PDF document if the newly downsampled image is in fact smaller than the original. When the downsampling process is combined with recompression, the output file that results can actually expand in size.  If the process yields an image that is the same size as the original, or larger, PDF Optimizer will leave the image alone.
consolidate-duplicate-image-and-forms Remove duplicate copies of alternate images and forms. This feature merges identical forms or images, as determined by an MD5 hash of their content.  The MD5 algorithm is used to create a 128 bit hash value that serves as a digest of a document or of a message of any length.  This hash value can be used to verify the original data later against any attempt to change the content or to make sure that the content was not corrupted during transmission. If hash values are created for images or form values in a PDF document, these values can be compared to each other to identify forms or images that are identical within that document.
down-convert-16-to-8-bpc-images When enabled, images that are 16 bits per component will be converted to 8 bits per component.

The color depth of an image is the number of bits used per pixel for each color component. RGB, for example, has three color components. By down-converting an image in a PDF file from 16 bpc to 8 bpc, you are reducing the resolution of the image, but also significantly reducing its size. If a PDF document features high-resolution images, the final PDF can also be significantly smaller.

This feature is not applicable if Color Conversion is enabled (see Color Conversion). Color Conversion will attempt to down-convert 16 bpc images automatically if you turn it on. The down-convert feature only has an impact if Color Conversion is turned off.