Nothing here reaches a server
The conversion runs as a few lines of arithmetic inside your browser tab. No values are logged, transmitted or retained, and the tool keeps working perfectly well after you disconnect from the internet.
A screen makes colour out of light, a press makes it out of ink, and the two will never fully agree, so run your shades through this colour converter for print first. Move between HEX, RGB and CMYK here, and find out early which ones are heading for a nasty surprise.
Edit any field and the others follow instantly, with a plain-English warning when the shade looks risky.
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Your monitor builds colour additively. It fires red, green and blue light at your eye and, at full strength, all three together produce white. A printing press works the opposite way, laying cyan, magenta, yellow and black ink onto paper that subtracts wavelengths from the light bouncing back off it. Two entirely different physical processes, asked to agree on the same design.
They cannot agree completely. The range of colours a screen can emit is considerably wider than the range four process inks can lay down, particularly at the vivid end. Those luminous cyans, acid greens and electric oranges that look extraordinary on a display have no ink equivalent, so the press quietly substitutes the nearest thing it can mix, and the result comes back flatter than you hoped.
The conversion in this tool is the standard textbook formula, and it is deliberately naive. Real conversion depends on an ICC profile that describes a specific press, specific inks and a specific paper, which is why the same file can produce noticeably different results at two printers. Treat these numbers as a starting point for the conversation, and let your printer's profile have the last word.
The conversion runs as a few lines of arithmetic inside your browser tab. No values are logged, transmitted or retained, and the tool keeps working perfectly well after you disconnect from the internet.
A large area of black built from black ink alone dries thin and patchy, and often reads as charcoal rather than true black. Build it from all four inks so the coverage is dense and even.
Add the four percentages together and most presses want the sum under about 300. Push past that and wet ink sits on the sheet too long, transfers onto the next copy and blocks in the stack.
Fine type should be pure K100 and nothing else. A rich black mix requires four plates to line up perfectly, and at eight or nine point any tiny misregistration puts coloured fringes around every letter.
We review your palette against your printer's profile, rebuild the risky shades, and flag anything that needs a proof before the run begins.
The problems that turn up most often when a cover designed on screen meets a four-colour press.
| Pitfall | What happens on press | Do this instead |
|---|---|---|
| Pure K100 across a large solid area | Prints as a flat grey-black with visible roller streaking | Use a rich black around C60 M40 Y40 K100 |
| Rich black behind small body text | Plate misregistration leaves coloured fringes on the letters | Set text under about 12 point in K100 only |
| Neon and fluorescent RGB values | Reproduce noticeably duller, sometimes by a whole tonal step | Choose a slightly muted equivalent, or budget for a spot ink |
| Total ink coverage over 300% | Ink refuses to dry, offsets onto the next sheet, blocks in the pile | Reduce the cyan and magenta, let the black plate carry the depth |
| Bright blue headline artwork | Drifts towards violet once magenta joins the cyan | Increase cyan, reduce magenta, then proof it |
| Grey built from equal C, M and Y | Wanders warm or cool as ink balance moves through the run | Build neutrals from the black plate alone |
| Trusting an uncalibrated monitor | Everything shifts, and you cannot tell which way | Order a printed proof before approving the run |
It depends on where it is going. Digital storefronts want RGB because the file is only ever displayed on screens. Physical printing generally wants CMYK, although some print-on-demand services now accept RGB and convert it with their own profile. Always check the specification for the exact service you are using.
Because you are watching the limits of ink demonstrated on screen. Process inks simply cannot produce every colour a backlit display can emit, so the conversion picks the closest achievable mix. Vivid saturated shades lose the most, which is why they look flattened after conversion.
Rich black is black ink supported by cyan, magenta and yellow underneath, commonly mixed around C60 M40 Y40 K100. Use it for large solid areas, full-bleed backgrounds and oversized display type, where black ink on its own would look weak and uneven.
One ink laid across a wide area cannot achieve full density. You get a slightly translucent charcoal, often with roller marks running through it, and it looks noticeably lighter next to anything genuinely black on the same sheet. Adding the other three inks fixes both problems.
It is the sum of all four percentages in a CMYK value. A colour at C60 M40 Y40 K100 totals 240%. Presses have a ceiling, usually near 300% for coated stock and lower for uncoated, above which the sheet is carrying more wet ink than it can absorb and dry.
No, and it does not claim to be. Photoshop converts through an ICC profile that models a particular press, ink set and paper. This tool uses the classic arithmetic formula, which lands you in the right neighbourhood but will not match a profiled conversion exactly.
Whichever one your printer names in their specification. In North America that is often US Web Coated SWOP, while European work commonly uses a Coated FOGRA profile. Ask before you export, because converting twice through the wrong profile degrades the file.
For a first print run, yes. No monitor, however well calibrated, shows you ink sitting on the specific paper your book will use. A physical proof costs very little compared with discovering that your carefully chosen cover blue arrived looking purple across a thousand copies.
Profile conversion, rich black construction, ink limits and bleed are all part of preparing a cover properly. Hand us the artwork and we will supply print and digital versions built to each specification.
See Book Cover Formatting