[Coco] [Color Computer] 1984 djvu conversion

[jasonb1963]

--- In ColorComputer at yahoogroups.com, "stinger30au" <stinger30au at ...> wrote:
>
> --- In ColorComputer at yahoogroups.com, "Mike Pepe" <lamune@> wrote:
> >
> > What is the benefit of turning a 300dpi PDF into a 400dpi djvu? Why
> > increase the resolution?
> > 
> 
> 
> Mike,
> i answered this question yesterday
> 
> djvu is a "lossy format"
> 
> if you take a 300dpi pdf & convert to 300 dpi djvu, you lose resolution and the text is blurry.this is due to th compression technique djvu uses.
> 
> if you wind up the resolution of the djvu to 400dpi the loss of quality is very small and the text is much sharper & jut as good as a 300 dpi pdf.
> 
> when i finish scanning the remainder of the aussie coco magazines i have and it will take me about 3 or 4 weeks maybe i will upload a pdf version of one just for you to do some tests on it yourself.
>

Meanwhile the 300DPI DJVU conversion of the January 1989 issue of Rainbow magazine is up on excalibur for comparison's sake.

BTW, Dez, the PDF format supports a number of different compression methods, some of which are lossy and some of which are not.  Depending on how your particular application is configured, you may or may not have any control over this (Adobe Acrobat allows you to control all of these options if you like, but it can be confusing until you spend a lot of time exploring all the options and see how they interact with your completed documents).  Also, I believe PDF "vectorizes" images (represents them as lines) whereas DJVU rasterizes images (represents them as dots) which is a fundamental difference in how they operate.  PDF gives excellent results for text documents but is less efficient for images and for scanned documents than DJVU.  They are both good at what they do, but for archiving older scanned documents, DJVU is hard to beat.  You might experiment a bit with the anti-aliasing option on DJVU to see if you are able to reduce the blurring you see at 300DPI.  If not, then your approach of going to a higher resolution seems like a reasonable alternative.

--
Jason