1200 dpi?

Hello,

Can someone explain to me why many manuals and guides ask that black and white lineart be provided at 1200 dpi, when the highest line screen values I've come across are 250 lpi, implying a resolution of no more than 500 dpi?

Clearly there's something I missing?

Thanks,

Ariel

1200 dpi?

It is very simple. A line screen is used to render a halftone pattern (artwork with different colors or shades of gray).

There are no halftones (grays/colors) in line art so no line screen is used. Ignore linescreen specs for line art.

1200 dpi?

Thanks Marian. A couple more questions:

(1) If I've got a PDF that contains both halftones and line art, how does the RIP know that the line art is line art and that it shouldn't screen it?

(2) (Almost certain of the answer here, but just in case) I take it that in this day and age there is no such thing as an actual ''screen'' -- it is simply a computer algorithm to simulate the result of a line screen? (Like Photoshop does when you convert a greyscale to bitmap)?

A PDF file can contain artwork of varying resolutions. When you use Distiller or any other Adobe PDF generator, you are given a window/panel to define different resolutions for different types of images (color, grayscale, monochrome [aka line art]).

Screening only occurs on art that is not 100% black. Line art is 100% black.

Yes, we do get a lot of terms from legacy processes and practices. It is still a digital screen.

This may illlustrate much:

http://en.wikipedia.org/wiki/Halftone

Actually, 1200 ppi is rather low for Black %26amp; White line art.?The differences between raster resolution ( i.e., 300 ppi ) vs. bitmap resolution ( 2540 ppi or even 5080 ppi is raster is continuos tone and bitmap is Black and White where White is transparent.?The reason for the, what seems like, very high resolution is because you need all of those bits to appear smooth to the naked eye.?This all can get very confusing very quickly.?Usually there is a corelation between your document resolution and bitmap resolution, so the RIP will know or have all of the information contained in the document.?This typically would mean 2540 dpi with a gradient mesh resolution of 300 ppi.?The 2540 dpi is the RIP's output resolution which should equal your bitmap resolution.?The raster resolution should equal twice the halftone screen's frequency ( i. e., 150 lpi ( lines per inch ) X 2 = 300 ppi ( image resolution ).

Now, you never see the halftone screen frequency because everything the creator creates is vector ( Illustrator / InDesign ) and/or bitmap ( Photoshop ) based files.?The ''screen'' is not created until the files are RIP'd and/or the press plates are generated for printing.?As stated already, even though the process is digitized, there still is a ''screen'' involved ( unless you are printed stochastically [ i.e., no screen, just random dots similar to inkjet ] ).

The actual process is a complex study in mathematics.?Let's say you have a piece of line art at 1200 ppi ( pixels per inch ) and you want it printed at 30% Black ( a screen tint if you will ).?If that bitmap artwork's resolution is too low and the screen frequency is high ( let's say 150 lines per inch ), then it may not screen smooth and may appear ''choppy'' to the human eye.?This all depends on the sophistication of the artwork.?Why??Because the screen frequency is going to reveal a lot of detail and if the artwork's res is at 1200 ppi, then the result will not be as smooth as the even higher bitmap res of 2540 ppi where the artwork is twice as smooth.

Adobe's user manuals explain resolution a bit more than I can here.?And most RIP manufacturers have guides ( which you've already seen ) that can help better understand the logistics.

John Danek wrote:

Actually, 1200 ppi is rather low for Black %26amp; White line art.

A PDF file can contain artwork of varying resolutions. When you use
Distiller or any other Adobe PDF generator, you are given a
window/panel to define different resolutions for different types of
images (color, grayscale, monochrome [aka line art]).

For instance, in the attached file, let's say the turtle is a line art scan at 1200dpi, and then there's the background at 300 dpi. I put the turtle image on top of the forest image in InDesign and export to PDF. Will the RIP be able to maintain the 1200 dpi resolution of the turtle?

(Hope you like my turtle!)

Ariel

Marian, no.?The line art does not become a raster image.?It remains line art even when it's being screen tinted.?Your explanation ( and mine ) of res twice the line screen applies to raster images ( photographs ) where the file is printed using four screen screens and their appropriate angles.?Optically, the human eye sees continuos tones.?But, if you screen a piece of line art ( which starts out as Black and White with no continuos tones ), it remains Black and White even when tinted ( there are no intermediate tones to smoothen the artwork ), therefore, the higher the res the better.?Otherwise, you run the risk of getting less than acceptable roughness in the smoothness of the artwork.?This is why 1200ppi is fine for a laser printer or an inkjet printer that will print at 1200 dpi.?A direct-to-plate system with RIP at 5080 dpi, giving it the ability to render a very fine halftone dot of 150 - 200 - 300 lpi.?If you feed that same RIP a 1200ppi line art image, the result will be a rough rendition of the artwork, certainly not a smooth as a 5080 ppi line art image.?I could be splitting hairs here, but if your file needs to hold critical detail and be as smooth as possible, the 5080 ppi would be best and 2540 ppi would be acceptable for line art images.?My brief explanation here applies to Black + White line art bitmap files.

If the line art is defining a solid ink (there is no screening/transparency), then the line art will render at 1200ppi.?The images are independent, even when overlaid. You can always try this with an extreme example. Set the line screen on your printer to something absurdly low... like 2 lpi (if it even allows such a low number).

John Danek wrote:

It remains line art even when it's being screen tinted.

If the line art is defining a
solid ink (there is no screening/transparency), then the line art will
render at 1200ppi.?The images are independent, even when overlaid.?
You can always try this with an extreme example. Set the line screen on
your printer to something absurdly low... like 2 lpi (if it even allows
such a low number).

Yes, I was responding to your post before the turtle.?The turtle example can help further with another demonstration. Try dropping the ppi of the photo to something silly like an effective resolution of 10 ppi. Then export from InDesign as a PDF/X1-a file. (The default resolution in this profile is 300 ppi for photos and 1200 ppi for your turtle line art.)?Zoom in on the PDF file in Acrobat/Reader to see the mushy nature of the photo but the line art is still crisp. This is a simple demonstration of how different elements can have different resolutions within PDF.?A normal RIP will respect these different resolutions.

A normal RIP will respect these different resolutions.

Yes, as you say, it is a pattern of dots when screened or let back to a tint value other than 100%. But the resolution of the Bitmap image has the same effective amount of information, or on off areas. Because it is made up of a finite amount of on and off switched for each of its boxes in the resolution matrix, in this case 1200 ppi. If you have a higher resolution in the output device then in the Bitmap file this only increase the boxes in the matrix which the on and off switches may occupy, it doesn't add any more switches. I however do find 1200ppi on a 2450dpi RIP with AM screening to be adequate for commercial printing.

Oh, and you seem to have a little somthing on your閳?a little smug, yeah right there.