Print quality: 100% K, vector, size
Why your barcode must be 100% K, not rich black
Short answer
A barcode must be printed in one ink, 100% black (C0 M0 Y0 K100), because a black made of several inks prints from several plates, and even a tiny shift between plates widens and blurs the bars. IngramSpark asks for black only, 0/0/0/100, and KDP's help words it as "100% black (not RGB/CMYK color or registration black)". 100% K is itself a CMYK value; what both platforms rule out is a black mixed from several inks, or an RGB black that gets converted into one. On screen you cannot see the difference; in the separations of the PDF you can.
Three kinds of "black"
| Name | CMYK values (example) | Plates it prints on | For a barcode |
|---|---|---|---|
| 100% K | 0 / 0 / 0 / 100 | Black only | Correct |
| Rich black | for example 60 / 40 / 40 / 100 | All four | Wrong |
| Registration | 100 / 100 / 100 / 100 | All four, and every spot plate | Wrong, and too much ink |
| RGB black | 0, 0, 0 in RGB | Depends on conversion, usually all four | Wrong |
Rich black is a perfectly good tool for large black backgrounds, where it gives a deeper black than ink alone. It is wrong for anything thin and precise: small text, hairlines and barcodes.
What happens on press
A four-color press prints each ink from its own plate, one after another. The plates are aligned (in register), but never perfectly: paper stretches, it moves slightly between units, and every press has tolerance. On a photo, a shift of a fraction of a millimeter is invisible. On a barcode it is not:
- The bars get wider. Four slightly offset bars cover more paper than one. A barcode encodes information in the exact widths of bars and spaces, so wider bars eat into the spaces.
- The edges get colored fringes. Cyan, magenta or yellow peek out at the edges. A scanner sees a soft edge instead of a clean one.
- The ink piles up. Four inks on top of each other can spread more on absorbent paper, which makes bars grow further.
With 100% K there is one plate, so there is nothing to fall out of register.
Where the black gets lost
Most designers set the barcode in black. The problem is that "black" in a design program is not always 100% K:
- RGB documents. In an RGB document, black is RGB 0,0,0. Converted to CMYK on export, it usually becomes a four-color black.
- Color conversion on export. A PDF export that converts colors to a destination profile can turn 100% K into a mix, or into a gray below 100%. IngramSpark warns about ICC profiles turning 100% black text into a shade of gray.
- Barcode from an image. A PNG or JPG barcode is RGB or grayscale. Placed in a CMYK cover and converted, its black usually becomes a mix.
- Default "rich black" swatches. Some templates use a rich black swatch named "Black".
How to keep it 100% K
- Start with a barcode that is already 100% K vector. Every Barcode Rocket PDF is C0 M0 Y0 K100.
- Place it, do not paste or recolor it.
- Export your cover PDF with a setting that does not convert colors (for example, "No Color Conversion" or "Preserve Numbers" in the output settings), or with your printer's preset if it keeps the K channel.
- Check the final PDF in Acrobat Pro, Output Preview, Separations: with only Black visible, the barcode must be complete. Step by step.
Overprint: on covers where black overprints the background, a 100% K barcode on a white box is safe either way, because there is nothing under it. On a colored background without a white box, the barcode would mix with the color below, which is another reason for the white box.
Frequently asked questions
Is a CMYK barcode OK?
Yes, if its CMYK values are C0 M0 Y0 K100. What is not OK is a black that also uses cyan, magenta or yellow (rich or registration black): it prints on several plates and can blur.
Will my printer fix it?
Not reliably. Some print workflows convert small black text to 100% K, but you cannot count on it for a barcode, and KDP and IngramSpark check it.
Does 100% K look gray?
On large areas, 100% K is slightly less deep than rich black. On thin bars on white, it looks black, and it is what every scanner expects.
My barcode is RGB 0,0,0. Is that black enough?
On screen, yes. In print, it depends on the conversion, and it usually becomes a four-color black. Use a barcode set in C0 M0 Y0 K100.
Sources
- Amazon KDP Help, Barcodes (100% black requirement): kdp.amazon.com
- IngramSpark, Understanding IngramSpark Title Processing (black only, 0/0/0/100): ingramspark.com
- IngramSpark Help, Cover File Creation (ICC profiles and 100% black): help.ingramspark.com
- Adobe Help, Previewing output (Acrobat Pro): helpx.adobe.com
- GS1 General Specifications (bar and space widths): ref.gs1.org/standards/genspecs