Knowledgebase: General
Image Quality
Posted by admin admin on 22 November 2006 06:01 PM
How do you increase the quality of images in a PDF file?
Poor image quality could be caused by a number of factors including:
-The resolution of the source image.
-The resolution of the screen or printer.
-The Win2PDF resolution.
-The zoom or scaling factor used to display the PDF.
-Image scaling that is done by the application before the image is sent to Win2PDF.
-The image compression performed by Win2PDF.
Win2PDF always renders bitmaps at the resolution selected in the "Printing Preferences->Advanced" window.  Increasing the Win2PDF resolution may improve the quality of the image.  If the source image is already lower than the Win2PDF resolution, then you won't see any improvement at higher resolutions.
Most screen displays have a resolution of about 96DPI, so you may not see an increase on screen even if the higher resolution image is embedded in the PDF.  You may have to zoom in or print the PDF to a higher resolution printer to see a difference.
Also, screen captures are low resolution bitmaps, and increasing the Win2PDF resolution above the captured resolution will have no affect.  The bitmaps can look lower in quality if Acrobat Reader is displaying the page at a magnification that isn't a multiple of 100%.  Changing the Acrobat Reader view options to 100 percent typically makes the document look better.
When the "Optimize Image File Size" option is enabled in the "PDF Options" window, Win2PDF compresses images using JPEG compression.  This can dramatically reduce the file size of the resulting PDF file, but it can reduce the quality of images.  If you uncheck the "Optimize Image File Size" option, it may improve the quality of images.
Adobe Reader "smooths" images by default.  This can improve the quality of some images, but it may make bitonal black and white images look gray.  If you uncheck the "smooth images" option in the Adobe Reader "Preferences->Page Display" dialog, it may improve the quality of black and white images.  The preferences dialog is under the "Edit" menu in Adobe Reader.
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