Re: [hylafax-users] hfaxd pdf2fax image quality

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Steven Jardine wrote:

> So . . . other than creating 2 sets of documents, 1 with halftone 
> black and white images and the other color, I am really stuck with the 
> poor quality?  Is there any other way to auto halftone or dither my 
> color or grayscale images? 


There are various dithering programs available out there... including 
ones that come with libtiff (tiffdither).  You could use ImageMagick 
among numerous other utilities out there.  Your biggest initial obstacle 
will probably be to get the PDF into a pure raster format (TIFF, JPEG, 
PNG, etc) rather than into a mixed vector+raster format that is PDF.  
(Dithering only applies to raster images.)

That said, it would be my advice to, yes, recreate the images that are 
placed into the documents for faxing purposes.  Recreate them in 
halftone with an absolute minimum amount of dithering.  Dithered images 
are much, much greater in data size when compared to similar 
non-dithered counterparts.  Thus, over time the dithering will end up 
costing you in increased communication time, increased risk of session 
problems, toll charges, etc.  Any time you have a transition 
horizontally or vertically that goes from black to white or white to 
black you decrease the effectiveness of the compression algorithms.  In 
fact, dithered images are often smaller *uncompressed* than they are 
when compressed because the compression actually increases the data size 
due to the frequency of horizontal and vertical black-white transitions.

Let's say that you have a logo that goes on every coverpage you send.  
Let's say that the logo has portions that are red, white, and blue.  
Instead of attempting to represent the various colors with a certain 
different speckle pattern of dots (usually trying to approximate the 
"darkness" of the tone) use non-speckled patterns such as checkerboards, 
wide stripes, simple outlines, or black-filled patterns.  It is a bit of 
an art form, yes.

Thanks,

Lee.


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