Are Your PDFs Causing Print Production Bottlenecks?
A reader asked, “Why are my PDF file sizes so big?”
There are several things that can cause PDF files to be larger than they need to be, but primarily it will be related to either the images or the fonts.
Some PDF files are created by scanning a printed sheet of paper. An uncompressed 8.5” x 11” image scanned at 600 DPI contains over 33 million dots. And if the image is in color, it may include require multiple bytes per dot. A 300 DPI image would only have ¼ as many dots as a 600 DPI image. So ask yourself, does this really need to be a high resolution image?
To determine if your document is a bitmapped image instead of text or vector images, you can run 2 tests.
- First, select a piece of text and copy and paste it into notepad. If notepad does not show you matching text, then it is likely that the text is really an image of text.
- Second, zoom in to 800% or more. Are the diagonal lines still smooth, or do they look like stair steps?
When you zoom in on a bitmapped image, you can see each square bit that makes up the image. Vector-based graphics and fonts stay smooth when they are scaled.
Most PDF images are compressed, which will reduce the file size greatly, but the quality of the image can impact its ability to be compressed. With compression, instead of storing black dot, black dot, black dot, black dot, black dot, black dot, black dot, black dot, black dot, black dot, black dot, black dot, black dot, white dot, white dot, white dot, white dot, white dot, white dot, white dot, white dot, white dot, black dot, black dot, black dot; what will be stored will be more like 13 black, 9 white, 3 black. Most compression algorithms condense both horizontally and vertically. A “clean” scan will compress more than a “dirty” scan because each flyspeck of dirt causes a color change.
Text will compress more than images, so if you can create your PDF from an electronic document format, rather than from the scan of a printed page, your file size will be much smaller. If your document is mostly text, rather than images, the issue may be the number and size of the fonts that are embedded in the PDF.
You can check File > Properties > Fonts in Adobe Acrobat to see how many fonts are embedded in your PDF document. If your PDF composition tool uses Type 1 or True Type scalable fonts, a single embedded font can be used for text in multiple point sizes. If your PDF file is built by concatenating multiple PDF files into one, you may actually have multiple copies of the same font embedded in the file.
Some freeware PDF creation tools may even embed every font on every page. PDF transform or PDF optimization software can be used to reduce the number of fonts included in the PDF. You can also reduce the file size by telling your creation software to subset the fonts as they are being embedded. A subset font will only contain the characters that are actually used in the document. If your document is in English, you probably wouldn’t need to embed the accented characters, Greek or Russian characters, or other special characters that might be included in the complete font. Embedding a subset font is especially important when working with Asian fonts that have hundreds of characters.
As you can see, several things can impact the size of your PDF. If you have investigated all the above and still have a PDF size problem and would like help with your PDF files, contact COPI using the Contact Us form below.
We will be glad to help.