Right amount of black for striped background

Question

I am creating a PDF document that has a table with pyjama stripes. The grey stripes are defined using RGB with equal amounts of each colour.

I'm want to make the stripes light enough so that you can write on a printed copy with a #2 pencil and easily read the text, yet dark enough so that the tables rows are easy to follow, both on screen and in print.

The PDF document will be printed on a wide variety of computer printers, but probably mostly on laser printers.

I've benchmarked the PDF on a Konica Minolta bizhub C550 printer and a Dell lcd screen and and 0.9 (=10% black) seems to be about right.

Now to my question:

At what blackness level will some computer printers print white instead of grey?

(I am aware that this question does not have an absolute answer, but your experiance and real-life examples are appreciated)

Side note (for extra credit):

I also have some other grey areas in my PDF. I noticed that as I reduced the blackness of the pyjama stripes the other grey areas became darker in the printed copy. I have verified that this is not just an optical illusion by cutting out the other grey areas and placing them next to each other. Why does this happen?

Edit (in response to JohnB's comment):

The choice of RGB over CMYK is a random one. If CMYK will result in better results I wouldn't mind switching. If you recommend a CMYK setting please be aware that I would rather not use the colour trays of printers that have separate trays for black.

Answer 1

I'd say 10%k.... but there's no telling what John Doe in Chattahoochie County uses as a printer.

5% has a tendency to drop off on lower-end home printers.

Most light greys tend to darken by 2-5% on end user printers (at least the ones I've seen)... so set it at 10% and hope the worst it gets is 15%. Better printers will hold the 10%.

There's really no way to answer this question specifically because there are just way too many variables. Best you can do is "shoot for the middle" and hope it's close when printed.

Answer 2

The Answer to the first part depends on the technology so you'll have to make concessions to allow for the differences.

I suggest that you consider readability over any other factor when considering among alternatives. How clearly and easily you can read the content, whatever your decision is about the background is where your first allegiance lies.

Minimum Black Tint for over-printing

Printing less than 3% is problematic. A 5% black tint will print on just about any printer with a clean marking engine. I'm sympathetic to your consideration for the cost of ink-jet refills, but black tints will compromise readability, somewhat by softening the appearances of the edges of the over-printed text. If you use a loupe for a close look, you'll see how lumpy the text edges appear. That's because the "grey" is really a bunch of small black closely-spaced dots. The screen also diminishes contrast which diminishes legibility.

Consider Perception

Cool colours make better background colours that comfortably "recede" into the background yet have enough contrast to aid horizontal visual alignment. A light blue works on the screen or on paper in a variety of tints that allow for any printer type (solid toner, ink jet, whatever). Try 10%. It can be written on easily. A close second would be as tint of green which has the advantage of being "in" this year. (Emerald is the 2013 colour.) Eye-savr™ green was de-rigeur for engineering schools for years.

Working with PDF

A possible reason for the darkening of the screened areas after changes may have to do with how the file was saved after the changes. Some software is sensitive to the difference between "Save" and "Save as…" The first appends changes to the file and the second over-writes the file. You'll have more consistent screen values after each modification if you perform a "Save as…" with some software products.

A frequently cited problem with PDF documents created for print production is that graphics that should be black-only ends up as RGB in the PDF file. It happens with images that started out in CMYK mode and Spot colours too.

The reason is that some applications do not create their own PS on printing; rather, they depend on the driver to generate PostScript for them. They use Graphics Device Interface which uses the RGB colour model. Some output devices will automatically convert RGB objects to CMYK. The net result produces a PDF with RGB black that will print with every pass of each of C M Y & K. It will appear darker.

You want to use applications that generate their own PostScript to avoid this problem. Adobe, Corel, Quark, and MacroMedia products don't have these problems. Microsoft does.