PDF Optimizer

Grayscale

downsample Ability to specify a target resolution and a trigger resolution at which grayscale images will be recompressed.
trigger-dpi All grayscale images above this resolution will be resampled.
target-dpi The new resolution of resampled grayscale images.
recompress Sets the type and quality of compression used to resample grayscale images.  Jpeg compression is a compression format used to render photographs as image files.  Also known as dct, Discrete Cosine Transform.
type same Keep original default compression algorithm provided in the images themselves
zip Use ZIP compression
jpeg Use JPEG compression
jpeg2000 Use JPEG2000 compression
quantity These values are valid for JPEG and JPEG2000 compression only:
minimum
low
medium
high
maximum
lossless Original quality of the graphic is preserved (see Monochrome). Only available for JPEG2000.

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.