#: 20139 S12/OS9/68000 (OSK)
    18-Jul-94  00:31:38
Sb: #20138-#mm2hp
Fm: LARRY OLSON 72227,3467
To: Bob van der Poel 76510,2203 (X)


 > You are completely correct that the program is trying to send more dots
 > than the printer can handle. However, I don't think that the answer is to
 > convert 8 bits to 7, etc. Remember, each byte of data is just a bit
 > stream...and the bits represent pixels. On a 256 color screen each byte
 > represents one pixel; on a 16 color 4 bits are 1 pixel. So what really
 > needs to be done is to take each pixel (4 or 8 bits) and convert that to a
 > grey scale (or even a color value if you are using a color ink jet
 > printer). It sort of works by just dumping the raster image...but it is not
 > the _correct_ way to do it.

   Bob,
       You are right that the pixels will need to be converted to a grey
   scale. Each screen byte would be changed to a 7 bit pattern, something
   like the following: ( assuming 256 color pixel)

     pixel value         7 6 5 4 3 2 1

       0 - 31            2 2 2 2 2 2 2

      32 - 63            2 2 2   2 2 2           2 = black

      64 - 95            2 2   2 2   2             = white

      96 - 127           2   2   2   2

     128 - 159             2   2   2  

     160 - 191               2   2    

     192 - 223                 2      

     224 - 255                        

     Then these 7 bit values would be packed back into 8 bit bytes to be
   sent to the printer.

       bytes to be set to printer
      byte 1             byte 2             byte 3             byte 4
  8 7 6 5 4 3 2 1    8 7 6 5 4 3 2 1    8 7 6 5 4 3 2 1    8 7 6 5 4 3 2 1
 _________________  _________________  _________________  _________________
 |1|2|3|4|5|6|7|1|  |2|3|4|5|6|7|1|2|  |3|4|5|6|7|1|2|3|  |4|5|6|7| | | | |
 |----- 1------|------ 2 -------|------- 3 ------|------- 4 ------|
   each pixel is represented by 7 bits

   My biggest problem at this point is the working with bits in C, I'm
 real shaky with C as it is, without doing this fancy stuff. 

   I'll let you know if I get anywhere with this



----- Larry Olson -----

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