Common Questions About the CMYK Simulator

The simulator is directionally accurate — useful for catching obvious problems before you send a file to print, but not a substitute for ICC-based soft proofing in Photoshop for production-critical decisions.

In practice: if the simulator flags a colour as out-of-gamut, it almost certainly is. If it shows TAC violations, they are real. If it shows a design looking significantly darker after dot gain, the print will also look darker. The simulator catches the categories of problems correctly, even if the exact values differ from a specific press.

For more: ICC profiles — what they are and when you need them →

No. Your image never leaves your device. The CMYK Simulator runs entirely in your browser using the HTML5 Canvas API and JavaScript. There is no server, no upload endpoint, no cloud processing, and no account required.

You can verify this yourself: open the browser dev tools (F12), go to the Network tab, then upload an image. You will see zero network requests triggered by the upload or processing. Everything happens locally in your browser's memory.

This also means the tool works offline. Once the page has loaded (the fonts and the JavaScript), you can disconnect from the internet and the tool will continue to work perfectly. It is one of the reasons the tool is open source — you can read the full source code on GitHub and verify this yourself.

The simulator accepts JPEG, PNG, and WebP files up to 5MB. Images larger than 1500px on their longest side are automatically scaled down to maintain performance.

For early-stage checking and education — yes, the simulator is genuinely useful. For final production approval on colour-critical work — no, it should not replace Photoshop ICC soft proofing.

The simulator has one significant advantage: it requires no software installation, no ICC profile downloads, and works on any device in under 30 seconds. For a freelancer checking a client design quickly, or a business owner previewing how their logo will print, it fills a real gap that Photoshop does not — because most people do not have Photoshop.

Learn more: What are ICC profiles and when do you need them →

Two separate reasons compound each other — and both are physical, not fixable by calibrating your monitor better.

Reason 1: Screens emit light. Print reflects it. Your monitor is an active light source — it fires photons directly at your eyes. Paper reflects ambient light from the room. Even a perfectly calibrated monitor will appear brighter than print because of this fundamental difference in physics.

Reason 2: Dot gain. A printing press creates tones using tiny halftone dots. A 50% grey on your design = dots covering 50% of the paper. When those ink dots hit paper, the ink physically spreads as it absorbs into the paper fibers — the dot grows. A 50% dot can print as 60–80% coverage depending on paper type. Everything gets darker, especially the midtones where faces, skin, and mid-grey backgrounds live.

The practical fix: if you are using Photoshop, load the correct ICC profile and enable View → Proof Colors. What you see then is an accurate simulation of how dark the print will be. Adjust your image's midtones upward to compensate before sending to press.

Full explanation: Dot gain — why print is always darker →

TAC — Total Area Coverage — is the sum of all four CMYK ink percentages at any given point in your design. The formula is simple:

Why it matters: every printing press has a maximum amount of ink it can lay down before it causes problems. Exceed the limit and ink does not dry properly — it stays tacky, smears on the next sheet, or soaks through to the back of the paper. Some printers reject files that exceed the limit. Others print them anyway and the result is a mess.

The simulator shows both the average TAC and maximum TAC across your entire image in the results panel, and compares them against the limit for the paper type you have selected. If the maximum TAC bar turns red, your file has areas that will cause print problems.

The red gamut overlay shows areas where your design contains colours that cannot be reproduced in CMYK print. These are called out-of-gamut colours.

Your monitor can display many more colours than a printing press can physically produce. Ink on paper absorbs light — there is a ceiling to how vivid and saturated a printed colour can be. When your design contains colours that exceed this ceiling, the printer does not crash or refuse to print — it silently replaces each out-of-gamut colour with the nearest reproducible equivalent. That nearest equivalent often looks noticeably different.

The colours most likely to be flagged are highly saturated RGB values — vivid oranges, electric blues, neon greens, and pure RGB primaries. These look spectacular on screen and disappoint badly in print.

More detail: The gamut problem — which colours shift and why →

This is the most common and most frustrating print problem — and it happens because the brand colour was originally chosen from an RGB colour picker without considering whether it could be reproduced in print. Here is exactly what to do:

• 1
  Open Photoshop. Create a new document in CMYK colour mode. Do not convert an existing RGB document — start fresh in CMYK.
• 2
  Open the Colour Picker. If the exclamation mark (⚠) appears next to your colour, that exact shade is out of gamut. Photoshop will suggest the nearest CMYK equivalent by clicking the ⚠ icon.
• 3
  Explore neighbouring CMYK values manually. Adjust the C, M, Y, K sliders rather than using the hex or RGB fields. Find the closest achievable colour that looks acceptable to you.
• 4
  Record the final CMYK values — e.g. C:0 M:65 Y:100 K:0. From now on, define your brand colour by these CMYK values, not by a hex code. Hex is an RGB-only notation and has no fixed meaning in print.
• 5
  If the shift is unacceptable — especially for a vivid orange or neon — consider a Pantone spot colour. Pantone inks are pre-mixed and not limited by CMYK gamut. They cost more (an additional press plate) but give exact colour matching.
• 6
  Request a physical press proof on the actual paper stock before approving the final print run. Even a correctly specified CMYK colour can look slightly different between paper types.

Full guide: What is CMYK and why your colours shift in print →

Choose the paper type that most closely matches what you are printing on. The selection changes the dot gain percentage, the ink limit threshold, and the gamut reduction applied to the simulation.

If you are unsure, ask your printer for the paper specification. The key terms to listen for: coated, silk, or gloss → choose Coated. Uncoated, matte, or offset → choose Uncoated. Newsprint or tabloid → choose Newsprint.

Learn more: Dot gain by paper type — exact numbers →

The dot gain slider controls how much the simulator darkens the midtones of your image to simulate the physical ink spreading on paper. Moving it higher makes the simulation darker and more compressed — as if printing on a more absorbent paper. Moving it lower produces a brighter result — as if printing on a very high-quality coated stock.

The effect is not a flat brightness adjustment. It uses a non-linear sine curve that applies maximum gain to the midtones (40–70% values) and minimum gain to the highlights and deep shadows. This matches how real dot gain behaves on press.

When you switch paper types using the buttons, the slider resets to the standard value for that paper. You can then override it manually — useful if your printer has given you a specific dot gain value for their press.

Full detail: Why dot gain is a curve, not a flat percentage →