Re: [APML] RGB -> CMYK

[Craig Utter <cmutter@bellatlantic.net>]

Title:

Larry McManus wrote:
> Hi Craig 
>   
>   
> >  
> >     
> > all right let's start on this one. 
> > the dot's do not change size or shape only quantity of the specific color,
> > in other words if an area of you image was pure magenta then all the dots
> > would be laid down with magenta ink. the actual size of the dots depends
> > on the line screen your using to reproduce the half tone, at Sky and Telescope
> > we use a 133 line screen.  
> >     
>  
> In a perfect world you are right. But in the imperfect world of paper, the
> dots will expand using an uncoated paper as opposed to using a cast coated
> paper. If you are laying down a solid magenta area there are no dots. 
Well, no that's not true with a halftone. even in an area that is nothing
but magenta there will always dots and all the same size. the dot expansion
is controlled by your "Dot Gain " setting in Photoshop. You need to make
sure this is set for the type of paper your using. Photoshop has some of
the settings already available in the color settings, there are some basic
setups for things like "sheetfed coated" or :sheetfed uncoated" and "web
coated" and uncoated. You can use these as a starting point.
>   
>   
>   
> Yes supply a press proof to your printer but then you have them supply you
> with a sample press run before they print the entire job. 
>   
> > NEVER TRUST YOUR MONITOR. No matter how much you fuss you 
> > will never have a 100% accurate rendition. RGB monitors pass light thru to
> > your eyes where as a printed page reflects light back to your eyes. The printed page will never look quite as bright or
> > show quite as much detail as you will see on your monitor, you need to work
> > by the "numbers". In Photoshop there is the "Info" palette, set this up to
> > read the images current color space as well as CMYK colorspace (you can do
> > this in Pallette options) when you pass the cursor over the image the info
> > pallette will display the number value for the area it's over. This way you
> > can see what the values will read in CMYK and if any exclamation marks "!"
> > appear next to the CMYK values that tells you that that particular area of
> > color is "Out of Gamut" and will not translate correctly in CMYK. 
> > I've found that Adobe Gamma is very effective for color management. 
> >     
>  
>   
> Nothing in printing is scientifically perfect. Unfortunatly  everyone has
> to deal with his or hers monitor. Your right there are things that you have
> to take into consideration when using your monitor. If you take those things
> into consideration then your monitor becomes your main tool. What you have
> described when using the out of gamut technique is mainly when creating color
> illustration. The best way to really check color work is to use the info
> pallette to get the numbers and check them against a CMYK swatch book. 
Actually you use a swatch book in Illustrator not in Photoshop. You need
to use the info palette to check the composition of your colors. There are
some basic rules for colors like black and white and neutral gray you have
to check to make sure the color components are balanced. If your reading
an area of  black sky in your image and it looks black to you but the CMYK
numbers read something like:

C-87%
M-45%
Y-74%
K-90%
Your going to end up with a green toned shade of black despite what you see
on your monitor. If you move the cursor over the standard black and white
color swatches you'll see what Adobe considers to be accurate blacks.


Craig Michael Utter

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