Default Valueĭatalogics::PDFL::PDFOptimizerDownsampleColorĭatalogics::PDFL::PDFOptimizerDownsampleGrayĭatalogics::PDFL::PDFOptimizerDownsampleBWĭatalogics::PDFL::PDFOptimizerDownSampleRecompressOnlyIfSmaller But the rendered quality of an image may decline. When it is used, it can save considerable space. Few PDF documents need to have alternate images any longer, because most rendering systems these days are able to adjust image resolution to match a display. Note that this process may discard higher resolution images in favor of images with lower resolutions. When enabled, all alternate images will be discarded, and only the primary image will be retained. If you know that higher resolution alternate images are no longer needed, because the PDF document will not need to be printed, these images can be removed from the file to reduce its size. In a common example, a PDF document could present one image with a lower resolution for display on a monitor, and an alternate image with a higher resolution to use when the PDF document is sent to a printer.īut alternate images can take a lot of space within the document, making the PDF a lot bigger. These images can be used to meet different needs. Removing Alternate Imagesĭatalogics::PDFL::PDFOptimizerDiscardAlternateImagesĪ PDF document can be set up to specify alternate images, or multiple versions of one image within the same document. We describe the parameters for optimizing images in this section. The downsampling process reduces the resolution of an image, and recompression involves using a different compression method to more efficiently reduce the size of an image. Because image recompression and downsampling are dependent on color type, we set up three classes for these functions, for color, gray scale, and black & white images. This section discusses downsampling and recompression with images in PDF documents. If you know that the images presented in the PDF document no longer need a high resolution-that is, you know that they are unlikely to need to be printed again-you may want to reduce the resolution you use for the document.
If you plan to send a PDF document as an email attachment, however, or transfer it using the File Transfer Protocol, you will probably want to make the PDF documents as small as you can.
So if you plan to send a PDF document to a printer with 1200 dots per inch resolution, you might want to use that resolution for images in your PDF document. That way, if the PDF needs to be downsampled for other renderings, these other renderings start from the original high resolution image. If an embedded image has a resolution that differs from the default resolution available at a target device, the Library will convert the image to the resolution for that target device. When creating a PDF document, then, it is best to include the highest resolution images that a potential rendering device can accept. Generally, when the Adobe PDF Library optimizes a PDF document, the system properly converts all the images in that document so that the colors remain consistent wherever the document is printed or displayed.
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