Author Topic: Can't get true black text in PDF  (Read 2451 times)

ginkgo100

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Can't get true black text in PDF
« on: August 06, 2015, 05:30:27 am »
I apologize if this issue has been covered before. I did search the web including this forum, but could not find an answer.

The short version of the question is, why can't I figure out how to get the exported PDF of a simple black-and-white document (text and grayscale images) to actually render the black as black instead of dark gray? I'm getting dark gray both on the screen and on the B&W laser printer. If you are familiar with this problem, you can probably skip all the rest of this post... help is appreciated!

Here is the long version:

I'm working on the black-and-white interiors of a couple of books. I noticed when I printed pages from the PDFs I generated on my B&W laser printer, the black text had little white halftoning dots—as if the printer were trying to render dark gray instead of “pure” black. I want the main text to come out as true, ordinary black—which (I guess) would be 0,0,0,100 in CMYK, or (what is to me) the equivalent of #000000 in RGB.

I tried fiddling around with some color settings, but couldn't figure anything out, so I did a systematic experiment with a test document. Here is what I found. I'm including a lot of details, sorry if they are irrelevant:

I'm using Scribus 1.4.4 in Windows 7. I'm viewing the PDFs with Adobe Reader X 10.1.15. All of my images were generated as either black-only or black-and-gray vector images in Inkscape, exported as PNGs.

Using the default settings (with the default text color presumably set to process black, or 0,0,0,100 in CMYK), if I take a screenshot of my monitor, the text color is actually RGB #161413 (that's HSV 20-13-8) rather than what I would reasonably expect, #000000. But maybe Scribus is trying to approximate the actual appearance of process black ink on white paper? If I then export a PDF for Screen/Web (using PDF 1.4 and without color management), however, the screenshot of Adobe Reader has the identical dark gray/black as the displayed text color.

I tried fiddling with the text color in Document Setup --> Tools, changing the text color and stroke to various CMYK and RGB colors, with various amounts of shading. This actually had *no effect* on the document's appearance. This seemed strange, but maybe the Default Paragraph Style (which I had defined as a particular font) was overriding it?

I changed the Document Setup --> Tools settings back to their original values, and tried exporting a PDF again, except with output for Printer. The PDF text was even lighter (RGB #231F20, or HSV 345-11-13). Finally I tried specifying output in Grayscale, and finally the text in Adobe Reader displayed as #000000. But when I applied the exact same settings to one of the real documents, it didn't solve the problem. After some more experimenting I discovered that if I introduce an image (black and white bitmap with anti-aliasing done using the alpha channel, as exported by Inkscape), the text reverts to that dark gray color for some reason, no matter what type of output I specify for the PDF (i.e. Screen/Web, Printer, or Grayscale).

I admit that I did not print a hard copy of each version of the experimental PDF, to see if the black really appeared to be solid black or if it had those little white halftoning dots.

Any help would be so appreciated!

utnik

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Re: Can't get true black text in PDF
« Reply #1 on: August 07, 2015, 10:24:17 am »
hi ginkgo

most office printer drivers work with rgb input.
cmyk 0, 0, 0, 100 is not a rich black like rgb 000000. if you provide a file in cmyk, the driver converts this tone to some rgb equivalent (like 1d1b1b) as its input value and  reconverts this really dark gray in the profile of the printer.

so you should probably feed your printer with a file in rgb (or in grayscale, if there's no other color used in the whole document…)

rgb 000000 and cmyk 0, 0, 0, 100 colors with output in 'grayscale' should print black.
rgb 000000 colors with output for 'screen/web' should print black.
every other combination (with one exception) may end in a dark gray.
the exception is a professional workflow with the correct output profile for your printer.

utnik
 

 

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