I just posted the stuff below to the Adobe forum (http://www.adobeforums.com/webx/.59b60ba6/1):
<begin post on Adobe forum> Aandi, you are right in _theory_. At 300 dpi it should not be noticeable in _practice_. And it isn't if you print the blurry pdf. The blur only appears on screen and it's due to a bug in Acrobat 8.1.2. Other pdf viewing software doesn't display the blur. It took me a while to figure out where the bug in Acrobat is. First I thought that it's the rendering of CCITT images because when you click on "Optimize Scanned PDF" the monochrome images get converted (and upsampled) to 600dpi CCITT. But I could easily create (with ImageMagick) 600dpi CCITT PDFs that are don't show up blurry in Acrobat. Only Acrobat's own production shows up blurry. Then it occured to me to extract the images from the blurry optimized pdf. Lo and behold, they are NOT rotated. What actually happens to monochorme images when you click on "Optimize Scanned PDF" is (i) image gets upsampled and converted to CCITT, and (ii) an external transformation matrix is stored in the PDF stream, but the image itself is not rotated (intenally)! For example, before "Optimize Scanned PDF" the matrix for image is q 595.1999969 0 0 841.9199982 0 0.0800018 cm /Im0 Do Q and after it becomes: q 424.0248718 -6.8531342 10.4018707 643.5963287 -5.1738739 3.4676819 cm /Im0 Do Q If you consult pages 208 and 339 in PDF 1.7 spec you'll see that the 2nd matrix has non-zero rotation. This is what Acrobat 8 cannot display properly, i.e. it blurs rotated CCITT images! Well it might blur other rotated images too, but I haven't checked. Below are links to before/after sample documents and before/after screenshots in podofo browser: http://www.cs.umd.edu/~gaburici/a8bug/page1orig+crop.pdf http://www.cs.umd.edu/~gaburici/a8bug/page1orig+crop+deskew.pdf http://www.cs.umd.edu/~gaburici/a8bug/orig.png http://www.cs.umd.edu/~gaburici/a8bug/deskewed.png </end post on Adobe forum> On Tue, Aug 5, 2008 at 4:44 AM, Glenn Linderman <[EMAIL PROTECTED]> wrote: > On approximately 8/4/2008 5:34 PM, came the following characters from the > keyboard of Vasile Gaburici: >> >> That does work, but the compression method used in the pdf is >> /CCITTFaxDecode. I'm trying to avoid that because Acrobat 8 has a >> stupid bug and displays these images blurred sometimes, even those it >> produced itself via "Optimize Scanned PDF", although other pdf viewers >> display them just fine. > > > Is it Acrobat, or Reader that has the bug? It is only version 8, or other > versions also? I notice in Reader 7 that Adobe seemingly attempt to do > antialiasing on the display of scaled B&W images, which blurs them slightly, > or so I thought it was doing -- maybe that is the bug you are referring to? > > I'd appreciate any additional information you have or can point me to about > this bug. Thanks. > > I use a lot of FAX Group 4 compression (/CCITTFaxDecode to Adobe), but > usually inside TIFF files and displayed with IrfanView. FAX Group 4 is a > lossless compression mode, except, of course, when actually sent via a FAX > connection! And except for .djvu, it is the most effective lossless > compression mode for B&W images that I am aware of. .djvu can usually halve > the file size for text images, though, but it is not common enough for > general use. > > > -- > Glenn -- http://nevcal.com/ > =========================== > A protocol is complete when there is nothing left to remove. > -- Stuart Cheshire, Apple Computer, regarding Zero Configuration Networking > > _______________________________________________ Magick-users mailing list [email protected] http://studio.imagemagick.org/mailman/listinfo/magick-users
