Convert PDF to grayscale and compress

Alec Jacobson

Recently I compressed a 25 MB color pdf to a 900 KB grayscale pdf. Here's how I did it:

Open the original.pdf in Preview. Select File > Save As... and choose Quartz Filter: Gray Tone. Save it as original_gray.pdf. My 25 MB color image was reduced to 13 MB by this step alone. Note: You could do this in Acrobat but it's much harder to find in the UI and actually crashed the program on my pdf.
Open original_gray.pdf in Acrobat. Select File > Save As... and choose Format: Acrobat PDF Files, Optimized. Then click Settings. Make sure Images is selected on the left. Change the color Downsample: line to Bicubic Downsampling to 200 ppi for images above 300 ppi Change the color Compression: line to JPEG, High Change the grayscale Downsample: line to Bicubic Downsampling to 200 ppi for images above 300 ppi Change the grayscale Compression: line to JPEG, High Change the monochromatic Downsample: line to Bicubic Downsampling to 72 ppi for images above 108 ppi Change the monochromatic Compression: line to CCITT Group 4 Note: You could do this in Preview with Quartz Filter: Reduce File Size, but some of images got their colors inverted.

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