[gs-bugs] [Bug 692279] New: Scaling 1 bit per pixel / component images in DeviceGray Colorspace

bugzilla-daemon at ghostscript.com bugzilla-daemon at ghostscript.com
Mon Jun 13 19:37:36 UTC 2011


           Summary: Scaling 1 bit per pixel / component images in
                    DeviceGray Colorspace
           Product: MuPDF
           Version: unspecified
          Platform: PC
        OS/Version: Windows 7
            Status: NEW
          Severity: normal
          Priority: P4
         Component: fitz
        AssignedTo: tor.andersson at artifex.com
        ReportedBy: danwaleke at quickenloans.com
         QAContact: gs-bugs at ghostscript.com
   Estimated Hours: 0.0

I have an application that converts PDF documents to 1 bit per pixel Tiff
images so they can be faxed.  The documents are converted to DeviceGray
colorspace and then an error diffusion algorithm is run on the images to
convert to 1 bpp/bpc Black/White.

If the source PDF contains a whole page image in BlackWhite 1 bpp/bpc
colorspace they are rendered in DeviceGray colorspace.  If the images are
scaled the resulting image created by MuPDF is no longer 1 bit per pixel.  The
problem with this is that the error diffusion algorithm ruins the documents
because they contain pixel values between 0 and 255 when they should only
contain 0 or 255 (Black or White).

Is there a way to tell MuPDF not to change the color of the pixels for 1 bit
per pixel images.  I.e leave all values 0 or 255 while scaling?

The output ends up looking like the scaled image was anti-aliased even though
that is being disabled with fz_set_aa_level(0).

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