Image DPI and Scaling, and Resultant File Sizes: Difference between revisions
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[[Image:PDFexport_dialog.png]] | [[Image:PDFexport_dialog.png]] | ||
Here we see 3 elements: '''Compression Method''', '''Compression Quality''', and '''Maximum Image Resolution'''. | Here we see 3 elements: '''Compression Method''', '''Compression Quality''', and '''Maximum Image Resolution'''. While it might seem that each of these would have some independent impact on the export PDF size, this isn't true. Let's attempt some sort of elucidation of how this works. | ||
Under the heading Compression Method we have the following choices: | |||
* Automatic | |||
* Lossy - JPEG | |||
* Lossless - Zip | |||
* None | |||
The tooltip here says: "Method of compression to use for images. Automatic allow Scribus to choose the best method. ZIP is lossless and good for images with solid colors. JPEG is better at creating smaller PDF files which have many photos (with slight image loss quality possible). Leave it set to Automatic unless you have a need for special compression options." | |||
Under the heading Compression Quality we have: | |||
* Maximum | |||
* High | |||
* Medium | |||
* Low | |||
* Minimum |
Revision as of 16:37, 20 October 2010
This article will show the results of some experimentation with modifying the scaling of images, and how this will affect PDF file size. The results are likely to surprise you, since first of all, this is not simply a matter of adjusting the scaling of the image in Properties > Image, since you can also set limits on the DPI and image quality at the moment you export to PDF.
Adjusting the Image File
Here is the simple Scribus document we will work with, a single US letter page with one image frame, and the entire image adjusted to frame size.
What's the Cost?
Now we'll load these 3 PDFs into Adobe Reader, view at 400% magnification, then capture a detail where we can see some sharp contours and big color changes.
553.5 DPI | 276.7 DPI | 138.4 DPI |
---|---|---|
Here we see why you get that warning when image resolution is below 150 DPI, but recall that this is a high magnification in Adobe Reader, so this pixelization could be quite acceptable for a PDF made for the web.
Another Method
There is another method or methods to reducing file size within Scribus, at the time of export. Look at this section of the PDF Export dialog:
Here we see 3 elements: Compression Method, Compression Quality, and Maximum Image Resolution. While it might seem that each of these would have some independent impact on the export PDF size, this isn't true. Let's attempt some sort of elucidation of how this works.
Under the heading Compression Method we have the following choices:
- Automatic
- Lossy - JPEG
- Lossless - Zip
- None
The tooltip here says: "Method of compression to use for images. Automatic allow Scribus to choose the best method. ZIP is lossless and good for images with solid colors. JPEG is better at creating smaller PDF files which have many photos (with slight image loss quality possible). Leave it set to Automatic unless you have a need for special compression options."
Under the heading Compression Quality we have:
- Maximum
- High
- Medium
- Low
- Minimum