We are printing a large (multi-hundred megabytes) pdf file, and large embedded PDFs are causing problems. A guy wrote up this documentation on making them smaller. (Thanks Barry!) It looked like something that others might find useful. So, the writeup… This assumes that you are shooting for a max PDF size of 5 megs.

How to make your figure smaller:

–Very Short Answer: Use the PDF Optimizer function, in the Advanced menu of Adobe Acrobat 7.0 Professional. Many files shrink a lot, with no change to the output image, when using the “First Try” settings I describe below. (These settings don’t alter the image quality at all, they just discard hidden junk.) If this does not work, you’ll have to think about downsampling, dpi and image compression, also described below.


–Medium-sized Answers:
-First try (simple!):
Set the options as specified as below in “Detailed Answers: 1. First Try”, then click “OK”.
Save your figure (e.g. myfig.pdf). to a different file name (myfig-opt.pdf) since you’ll need the original if the first try doesn’t get the figure small enough. Processing should take Acrobat a minute or so. (Also, save your option settings to a Preset, to save time in future.) Open and enjoy the smaller-file-sized, identical-appearing figure.
Random .pdf files shrank, using only this method:
22 MB -> 5 MB
5.4 MB -> 2.4 MB
5.6 MB ->1.8 MB
-More tries (less simple):
If that doesn’t get file small enough, try it with some downsampling, then try adding ZIP compression, and then try high quality JPEG compression. Details on this below. You’ll want to keep an “effective” 200 dpi or more (see below).


–Detailed Answers:
1. First try: Process your file with Adobe Acrobat 7 Professional’s PDF Optimizer function (located in Advanced menu)

a) Set options In PDF Optimizer window:
Choose Preset: Standard then make these changes:
Images:
Color Images:
Downsampling=off
Compression=Retain existing
Grayscale Images:
Downsampling=off
Compression=Retain existing
Monochrome Images:
Downsample=off
Compression=CCITT Group 4

Discard Objects:
Check all boxes _except_ convert smooth lines to curves.
(this will not affect image at all, but discard unused parts)

b) Save your settings to a preset like “my-lossless-no-downsample” (see the rectangular Save button on the top of the PDF Optimizer window) so you don’t have to enter the above options again.
c) Click OK
d) Save your figure (e.g. myfig.pdf). to a different file name (myfig-opt.pdf) since you’ll need the original if the first try doesn’t get the figure small enough.
e) Processing should take Acrobat a minute or so.
f) Examine size and quality of new file, check on screen or print out and compare.

If this does not get file small enough, try to play with downsampling and lossy image compression. Note that dpi will depend on image size, and actual destination dpi will depend on how you scale your figure. Adjust dpi numbers to reflect destination dpi.

2. If result > Max File Size (5 MB)
Starting from original file, repeat w/
Downsampling =bicubic downsampling to 300 dpi for greyscale and color images. (Very mild effect on image, our 600 dpi greyscale printer, for example, can’t do much past 200 lpi (lines per inch) for greyscale. Lines-per-inch which is what the greyscale dpi translates to on printers. Same idea for color printer.)

3. If result > Max File Size (5 MB)

Starting from original file, repeat w/
Bicubic downsampling to 300 _effective_ dpi for greyscale and color images
Compression ZIP

4. a) If result > Max File Size (5 MB)

Starting from original file, repeat w/ Compression JPEG, High

or

b) Repeat w/
Bicubic downsampling to 200 _effective_ dpi for greyscale and color images.

5. If result > Max File Size, do as in 4., w/ downsampling set to 200 effective dpi, and medium JPEG compression.

What “effective dpi” means:
(As stated above) You’ll want to keep an “effective” 200 dpi or more — that is, dpi as your figure is formatted on the printed page — for grayscale/color images, to look best on printout. If your image had to be scaled 50% to fit on a page (for example, an 8-inch-wide figure with [width=4inch] in your latex figure environment) then instead of asking Optimizer to downsample to 200 dpi you’ll downsample to (0.50 * 200 dpi) = 100dpi.
You might object: but printers are 600 dpi! Yes, but for color and grayscale printers, they combine patterns of dots to make color/grayscale, called lines-per-inch resolution, and 200 lpi is about their limit.

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