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Print my princexml book on lulu.com

pelrol
Hi, I've generated a PDF file from posts dumps of my blog with princexml, and tried to print it with luluservices.

They've sent me an email to tell me they can't print that PDF file:
lulu support wrote:
Thank you so much for contacting us about your order ( XXXXX ). We were unable to print this book due to some issues in your files. Your interior content PDF had transparencies and many images over 600 dpi. Also, you used a PDF creator that we are not familiar with at all. You will need to address each of these things. First of all, make sure that the PDF is completely flat and that no layers are preserved in order to get rid of the transparencies that are present. Next, make sure all images are less than 600 dpi. Otherwise, your file will load very slowly at the printer. Finally, I suggest you create you PDF in another way. Adobe PDFs are the gold standard in the print world, and if Adobe Acrobat is not available to you then visit acrobat website to make up to 5 Adobe PDFs for free.


Concerning, the image resolution, I found the "prince-image-resolution" CSS property, but I don't know how to fix the transparency and layer issues.

Anybody can help ?
Thanks a lot.
mikeday
The image resolution will need to be reduced by scaling down the images themselves, as the prince-image-resolution property is only used to tell Prince the resolution in order to determine an appropriate size, it does not affect the resolution of the images embedded in the PDF file.

Regarding transparency, are you using images that include an alpha channel, such as PNG images?
pelrol
I would say no, but the smileys included in my blog posts are pretty much the same as the ones in this forum : http://www.famillepellegrin.fr/blog/wp-includes/images/smilies/icon_smile.gif

Meaning the do have a transparency information ...
Do I also have to edit them to put a white background instead of a transparent one ?

Too bad prince does not have an option to resize pictures on the fly :(
mikeday
Yes, those kind of GIF images will be including transparency information; placing them on a white background will solve this.

Prince cannot scale down images at the moment, although it does have a property for reducing the quality of large JPEG images. However, are you really using many images over 600dpi on your website? Most images online are only 72 or 96dpi.
pelrol
The thing is that in my blog posts I have thumbnails pictures (that are probably 96 dpi) with link to the full size one (6Mpix), but as I want to get a good printing quality for my images in the book, I am replacing the thumbnails with the full size ones and keeping the width an height img tag properties to get the correct posts layout.

I am probably doing it wrong, and maybe I should use an intermediate size for pictures to be printed.
mikeday
Reducing the images to 300 or 450dpi should solve the problem, while still keeping adequate resolution for high-quality printing.