Is it possible to change the DPI of embedded TIFF images?
No. The DPI of the image within a PDF is static. Foxit PDF SDK does not have the feature to upscale a image DPI if the image already exist. The workaround is to upscale the image using a third party library and then add it to the PDF.
Foxit PDF SDK does have a FSCRT_ImageFile_SetProperty in which you can set the FSCRT_IMAGEPROPERTY_DPI property value, however, it only support images created inside the application by using “FSCRT_ImageFIle_Create and FSCRT_ImageFile_AddFrame and it does not support JPX, GIF and TIF formats.
Note: This article refers to a deprecated version of a Foxit Product. If you are still using Foxit PDF SDK 5.3 or older, please refer to your download package documents for Developer Guide and API Reference.
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Updated on September 14, 2017