Digital BW, The Print

To help me with the adaption of the Wasatch SoftRip for quad
printing a friend wrote a small PC application to convert 8 bit
and 16 bit greyscale files to plain 8 bit or 16 bit cmyk files.
No separation is done just 4 copies of the greyscale gathered and
given the C,M,Y,K, mark. Similar to what can be done with a
PhotoShop action. He also added a choice of compression, LZW,
ZIP, RLE or none. The ZIP compression is not accepted by the RIP
but PhotoShop does, with that kind of CMYK files the size is then
a bit smaller than the original greyscale file.
I wonder whether it has any sense to make the application
available on my site, with the LZW compression added it isn't
wise to put in the file section of this list.

Following a small thread here (OPM in theory) on the conversion
of 8 bit greyscale to 16 bit I asked him whether it could be
added to the same application with the bit shifts as discussed
here. He made some comments I like to add (my translation):

Quote:
From the discussion I gather there are three variants:

i8  :   8 bits grey values (0-255)
i16: 16 bits grey values (0-65535)

A) i16 = 256*i8
B) i16 = 257*i8
C) i16 = 256*i8 + random(0,256)

I consider B to be the only correct one. With that the complete 8
bit intensity range is scaled to the complete 16 bits range.
Software writers tend to do A that gives a small offset and a bit
lower contrast. Some people in the discussion had high hopes for
C. I don't get how you can get a better result by introducing a
random falt of half the step value on purpose. Best guess is that
it tries to generate a random dithering. I seems to me that the
dithering process should be done on results obtained with exact
computations.

If there's a desire to experiment I can add a 8-16 bit conversion
option with a choice between B and C. Any thoughts on the random
function in C are welcome. It can be a uniform distribution where
all the numbers get an equal chance. A normal distribution may be
better, the numbers further from the middle get a lower chance.

Gert-Jan

End of quote, translation by Ernst


Ernst