Digital BW, The Print

Hello George,

>2.I read in Clayton Jones' online articles that after turning an 
>image to monochrome in channel mixer, I should convert it to 
>grayscale (image/mode) before doing my work and then back to RGB 
>again before printing. 

Are you sure I said this?  I don't ever do this (change back to RGB
for printing).  Which article was it?  The only places (I think) that
I discussed this subject were in Articles #7 and #9.  I just looked at
those to be sure and didn't see anything about changing back to RGB. 
I'm wondering if you are mixing this with Paul Roark's RGB printing
techniques?



>It also suggest converting to 16-bit to do work on the image, and 
>then back to 8-bit before printing. I've always worked in 8-bit 
>RGB and never converted to grayscale or 16-bit before. What is the 
>purpose of this...

Working in 16 bit avoids the heavily combed histograms (which can
cause posterization in the prints) that result from applying curves,
levels and other manipulations.  Changing back to 8 bit is because
once the work is done 16 bit isn't needed any more (the image is
converted to 8 bit by the printer driver when it sends it to the
printer).  Going back to 8 bit reduces the file size by half.  But,
you want to be sure that all the work is done.  I usually wait until
I'm really certain I won't be doing any more manipulation.

As for changing from RGB to grayscale, in my experiments I have never
found an advantage to staying in RGB (the resulting prints are a tiny
bit different, but not better).  Going to grayscale reduces image size
by 2/3.  

For example, a 16 bit RGB tiff from my 8 mp digicam is about 45mg
after conversion from RAW.  Going to 16 bit grayscale makes it 15 mg.
Going to 8 bit when I'm done working on it reduces it to 7.5 mg.  The
print quality from each of them is the same.

I have even found an advantage in converting an 8 bit RGB from my
pocket camera to 16 bit before conversion to BW.  It's not the same as
an original 16 bit file, but it does help reduce combing.  I recently
found an article on Keith Cooper's web site that explains why:

http://www.northlight-images.co.uk/article_pages/16_bit_black_and_white.html


Regards,
Clayton


Info on black and white digital printing at    
http://www.cjcom.net/digiprnarts.htm