{"course":{"slug":"ai-images","title":"Image Generation, in Practice","url":"https://addaly.com/learn/ai-images","level":"beginner","track":"create"},"lesson":{"slug":"colour-for-the-medium","title":"The blue on your screen is not going on the press","url":"https://addaly.com/learn/ai-images/colour-for-the-medium","position":64,"of":69,"minutes":8,"answer":"Screens emit light and presses absorb it, so a set of vivid screen colours cannot be printed at all.","keyIdea":"Screens emit light and presses absorb it, so a set of vivid screen colours cannot be printed at all, and the conversion has to be seen and approved before delivery rather than discovered on the printed sheet."},"body":{"format":"markdown","text":"## Two different physics\n\nA screen makes colour by emitting red, green and blue light. Add all three and you get white. A press makes colour by putting cyan, magenta, yellow and black ink on paper that absorbs some light and reflects the rest. Add all four and you get a muddy dark brown, which is why black is printed separately.\n\nThese produce different ranges of reproducible colour, and the screen's is larger in the areas people care about most: saturated blues, vivid greens, bright oranges, anything neon.\n\nSo some colours you can see on a monitor cannot be printed. Not \"printed slightly differently\": cannot be printed. The press substitutes the nearest available colour, and a vivid cyan-blue arrives as a duller, greyer blue.\n\n## What actually happens\n\nA generated image is in sRGB. Converting it to CMYK for print maps every out-of-range colour to the nearest reachable one. The typical result:\n\n- Saturated blues lose vibrancy and shift toward purple or grey.\n- Bright greens dull noticeably.\n- Vivid oranges and reds lose their glow.\n- Deep blacks become lighter unless a rich black is specified.\n- Subtle gradients can band.\n\nIf the image was graded to look good on a screen, this conversion can be a shock.\n\n## Soft proofing, free\n\nYou can see it before printing. GIMP has soft-proofing built in: `View > Color Management > Soft-Proofing Profile`, pick a CMYK profile, and enable the gamut warning, which marks unprintable colours in a flat grey.\n\nTwo decisions follow from what you see:\n\n**If little is flagged**, proceed. Convert at export and it will be fine.\n\n**If a large area is flagged** (a sky, a background, the brand colour) fix it now. Reduce saturation in that range, or re-grade the image toward colours the process can reach. Doing this yourself gives a controlled result; letting the converter do it gives whatever the algorithm decides.\n\nScribus does the same and is the better tool if the image is going into a layout anyway.\n\n## Practical rules\n\n**Work in RGB, convert at the end.** RGB is a larger space and you keep more information through the editing. One conversion, at export.\n\n**Ask which profile.** Different presses and papers use different profiles: coated and uncoated stock differ substantially. The printer will tell you, and using theirs beats guessing.\n\n**Black is not black.** 100% K alone prints as a washed dark grey on large areas. A rich black (around 60C 40M 40Y 100K, though printers vary) is what you want for large solid blacks. Ask.\n\n**Colour on uncoated paper is duller.** The ink sinks in. Everything is softer and lighter than on coated stock, and this surprises people more than the gamut conversion does.\n\n## Screen has its own version of this\n\nNot a gamut problem but a consistency one. Your monitor is not calibrated, the client's is different, and phones apply their own processing. An image graded on a warm, bright laptop will look cold and dark on somebody else's cheap external display.\n\nTwo mitigations that cost nothing. Check on a second device, ideally a phone, before sending. And avoid grading to the edges: an image that depends on the last 5% of shadow detail will lose it somewhere.\n\nIf you have a colorimeter, calibrate; if not, at least set the display to a neutral factory profile rather than a vivid picture mode.\n\n## The position\n\nThe vector-and-print course in this catalogue covers preparation for press properly: bleed, marks, overprint, profiles, preflight. What matters here is timing: **the colour conversion is a decision made while the image can still be changed**, not a checkbox at export.\n\nAnd a limitation worth stating plainly: there is no way to make a printed image match a screen exactly, because the two are physically different media. The goal is a printed result you have seen, approved and are not surprised by. A client who says the printed poster looks duller than the screen is describing physics, and the conversation goes very differently depending on whether you showed them a soft proof beforehand."},"check":{"question":"Why can a vivid cyan-blue on screen not be reproduced on a CMYK press?","options":[{"text":"Because CMYK uses four inks rather than three channels, so the additional black plate desaturates colours as it is applied.","correct":false,"tempting":"Black is added for density and detail and is not applied to pure saturated areas; the limit is what the inks can reflect, not the number of plates."},{"text":"Because screens emit light while inks absorb it, and the reachable colour range of the two processes genuinely differs.","correct":true},{"text":"Because the conversion to CMYK is performed at 8 bits per channel, which is insufficient to represent highly saturated colours without quantisation.","correct":false,"tempting":"Bit depth affects banding in gradients rather than which colours are reachable; the same limit applies at 16 bits."},{"text":"Because print colour is measured under a standard illuminant that is dimmer than a backlit display, so all printed colours appear less saturated by comparison.","correct":false,"tempting":"Viewing conditions do affect appearance, and the blue would remain unreachable even under bright light."}]},"prev":{"slug":"resolution-you-actually-need","title":"300 dpi is one number applied to everything","url":"https://addaly.com/learn/ai-images/resolution-you-actually-need"},"next":{"slug":"type-over-an-image","title":"Making words readable on a photograph","url":"https://addaly.com/learn/ai-images/type-over-an-image"},"authorship":"Founder and series editor: Dr Mustafa Mun. Written by AI models to a written standard. Exam keys checked blind by a second model: 3,665 of 3,666 agreed. Academic review invited.","review":{"status":"Draft, open for academic review"},"cite":"Addaly (2026) 'The blue on your screen is not going on the press', in Image Generation, in Practice. Edited by M. Mun. Addaly. Available at: https://addaly.com/learn/ai-images/colour-for-the-medium (Accessed: 13 October 2026).","licence":{"name":"CC BY-NC-SA 4.0","url":"https://creativecommons.org/licenses/by-nc-sa/4.0/"},"reader":{"schema":1,"title":"The blue on your screen is not going on the press","courseTitle":"Image Generation, in Practice","module":{"index":7,"slug":"finishing","title":"Finishing and handing over"},"answer":null,"keyIdea":"Screens emit light and presses absorb it, so a set of vivid screen colours cannot be printed at all, and the conversion has to be seen and approved before delivery rather than discovered on the printed sheet.","hero":{"kind":"plate","image":null,"alt":null,"caption":null},"blocks":[{"t":"h2","id":"two-different-physics","runs":[{"text":"Two different physics"}]},{"t":"p","runs":[{"text":"A screen makes colour by emitting red, green and blue light. Add all three and you get white. A press makes colour by putting cyan, magenta, yellow and black ink on paper that absorbs some light and reflects the rest. Add all four and you get a muddy dark brown, which is why black is printed separately."}]},{"t":"p","runs":[{"text":"These produce different ranges of reproducible colour, and the screen’s is larger in the areas people care about most: saturated blues, vivid greens, bright oranges, anything neon."}]},{"t":"p","runs":[{"text":"So some colours you can see on a monitor cannot be printed. Not “printed slightly differently”: cannot be printed. The press substitutes the nearest available colour, and a vivid cyan-blue arrives as a duller, greyer blue."}]},{"t":"h2","id":"what-actually-happens","runs":[{"text":"What actually happens"}]},{"t":"p","runs":[{"text":"A generated image is in sRGB. Converting it to CMYK for print maps every out-of-range colour to the nearest reachable one. The typical result:"}]},{"t":"ul","items":[[{"text":"Saturated blues lose vibrancy and shift toward purple or grey."}],[{"text":"Bright greens dull noticeably."}],[{"text":"Vivid oranges and reds lose their glow."}],[{"text":"Deep blacks become lighter unless a rich black is specified."}],[{"text":"Subtle gradients can band."}]]},{"t":"p","runs":[{"text":"If the image was graded to look good on a screen, this conversion can be a shock."}]},{"t":"h2","id":"soft-proofing-free","runs":[{"text":"Soft proofing, free"}]},{"t":"p","runs":[{"text":"You can see it before printing. GIMP has soft-proofing built in: "},{"text":"View > Color Management > Soft-Proofing Profile","code":true},{"text":", pick a CMYK profile, and enable the gamut warning, which marks unprintable colours in a flat grey."}]},{"t":"p","runs":[{"text":"Two decisions follow from what you see:"}]},{"t":"p","runs":[{"text":"If little is flagged","b":true},{"text":", proceed. Convert at export and it will be fine."}]},{"t":"p","runs":[{"text":"If a large area is flagged","b":true},{"text":" (a sky, a background, the brand colour) fix it now. Reduce saturation in that range, or re-grade the image toward colours the process can reach. Doing this yourself gives a controlled result; letting the converter do it gives whatever the algorithm decides."}]},{"t":"p","runs":[{"text":"Scribus does the same and is the better tool if the image is going into a layout anyway."}]},{"t":"h2","id":"practical-rules","runs":[{"text":"Practical rules"}]},{"t":"p","runs":[{"text":"Work in RGB, convert at the end.","b":true},{"text":" RGB is a larger space and you keep more information through the editing. One conversion, at export."}]},{"t":"p","runs":[{"text":"Ask which profile.","b":true},{"text":" Different presses and papers use different profiles: coated and uncoated stock differ substantially. The printer will tell you, and using theirs beats guessing."}]},{"t":"p","runs":[{"text":"Black is not black.","b":true},{"text":" 100% K alone prints as a washed dark grey on large areas. A rich black (around 60C 40M 40Y 100K, though printers vary) is what you want for large solid blacks. Ask."}]},{"t":"p","runs":[{"text":"Colour on uncoated paper is duller.","b":true},{"text":" The ink sinks in. Everything is softer and lighter than on coated stock, and this surprises people more than the gamut conversion does."}]},{"t":"h2","id":"screen-has-its-own-version-of-this","runs":[{"text":"Screen has its own version of this"}]},{"t":"p","runs":[{"text":"Not a gamut problem but a consistency one. Your monitor is not calibrated, the client’s is different, and phones apply their own processing. An image graded on a warm, bright laptop will look cold and dark on somebody else’s cheap external display."}]},{"t":"p","runs":[{"text":"Two mitigations that cost nothing. Check on a second device, ideally a phone, before sending. And avoid grading to the edges: an image that depends on the last 5% of shadow detail will lose it somewhere."}]},{"t":"p","runs":[{"text":"If you have a colorimeter, calibrate; if not, at least set the display to a neutral factory profile rather than a vivid picture mode."}]},{"t":"h2","id":"the-position","runs":[{"text":"The position"}]},{"t":"p","runs":[{"text":"The vector-and-print course in this catalogue covers preparation for press properly: bleed, marks, overprint, profiles, preflight. What matters here is timing: "},{"text":"the colour conversion is a decision made while the image can still be changed","b":true},{"text":", not a checkbox at export."}]},{"t":"p","runs":[{"text":"And a limitation worth stating plainly: there is no way to make a printed image match a screen exactly, because the two are physically different media. The goal is a printed result you have seen, approved and are not surprised by. A client who says the printed poster looks duller than the screen is describing physics, and the conversation goes very differently depending on whether you showed them a soft proof beforehand."}]}],"check":{"question":[{"text":"Why can a vivid cyan-blue on screen not be reproduced on a CMYK press?"}],"options":[{"text":[{"text":"Because CMYK uses four inks rather than three channels, so the additional black plate desaturates colours as it is applied."}],"correct":false,"tempting":[{"text":"Black is added for density and detail and is not applied to pure saturated areas; the limit is what the inks can reflect, not the number of plates."}]},{"text":[{"text":"Because screens emit light while inks absorb it, and the reachable colour range of the two processes genuinely differs."}],"correct":true,"tempting":null},{"text":[{"text":"Because the conversion to CMYK is performed at 8 bits per channel, which is insufficient to represent highly saturated colours without quantisation."}],"correct":false,"tempting":[{"text":"Bit depth affects banding in gradients rather than which colours are reachable; the same limit applies at 16 bits."}]},{"text":[{"text":"Because print colour is measured under a standard illuminant that is dimmer than a backlit display, so all printed colours appear less saturated by comparison."}],"correct":false,"tempting":[{"text":"Viewing conditions do affect appearance, and the blue would remain unreachable even under bright light."}]}],"order":[3,1,0,2],"why":null},"prev":{"slug":"resolution-you-actually-need","title":"300 dpi is one number applied to everything","minutes":8},"next":{"slug":"type-over-an-image","title":"Making words readable on a photograph","minutes":8}}}