Optimizing images in your PDFs allows you to create the perfect balance between file size and visual quality, depending on how your files are to be used. There are two primary techniques used in optimizing images: compression and downsampling.
Downsampling reduces image resolution by lowering the number of dots per inch (DPI) that the image contains. Since there is less information that needs to be saved, the resultant PDF file sizes can be considerably smaller. In general, it is a good idea to downsample images based on the resolution of the device you are sending the file to. For example, typical computer monitors have a resolution between 72dpi and 96dpi, which is the highest resolution the monitor can display.
The following image optimization settings are available when using the Resample images option after selecting Custom for Nitro Pro’s Optimize PDF tool:
Creates files optimized that are optimized for on-screen viewing. Images will be compressed using the JPEG compression technique, and images with resolution greater than 150dpi will be downsampled. Use this setting when you want to create the smallest possible file size and where print quality is less important than file size, for example in preparing PDFs for display over the web.
Creates files that are optimized for printing to standard home or office printers. Images will be compressed using the ZIP compression technique, and images with resolution greater than 300dpi will be downsampled. Use this setting when you want to create a file that retains decent print quality when printed to a general use printer, while remaining relatively compact in terms of file size, for example in preparing PDFs for emailing to coworkers.
Allows you to specify different settings for various types of images contained within your document, for example color or grayscale images. Depending on the types of images contained in your document, available options include: