About

Print production requires CMYK values, not RGB. A color that renders correctly on screen at R=255, G=0, B=0 maps to approximately C=0%, M=100%, Y=100%, K=0% in subtractive color space. Incorrect conversion causes color drift on press, wasting ink and substrate. This tool extracts dominant colors from uploaded images using a Median Cut quantization algorithm, then converts each centroid from the additive RGB model to the subtractive CMYK model using the standard formulaic decomposition with a Key channel. The conversion assumes a standard SWOP coated profile approximation. It does not perform ICC profile-based separation. For critical prepress work, validate extracted values against your printer's specific ICC profile.

Formulas

The RGB-to-CMYK conversion normalizes each channel to the range [0,1], computes the Key (black) channel, then derives Cyan, Magenta, and Yellow relative to the remaining colorant capacity.

R′ = R255 G′ = G255 B′ = B255

K = 1 − max(R′, G′, B′)

C = 1 − R′ − K1 − K M = 1 − G′ − K1 − K Y = 1 − B′ − K1 − K

{

C, M, Y = 0 if K = 1formulas above otherwise

Where R, G, B are the 8-bit channel values [0 - 255], and C, M, Y, K are expressed as percentages [0% - 100%]. The total ink coverage TIC = C + M + Y + K should generally not exceed 300% for coated stock or 260% for uncoated to prevent drying issues.

Reference Data

Color Name	HEX	C%	M%	Y%	K%	Use Case
Process Black	#000000	0	0	0	100	Body text, outlines
Rich Black	#090415	60	40	40	100	Large solid areas
Pure Cyan	#00AEEF	100	0	0	0	Spot highlight
Pure Magenta	#EC008C	0	100	0	0	Accent / branding
Pure Yellow	#FFF200	0	0	100	0	Warning / highlight
Reflex Blue	#001489	100	73	0	2	EU flag, corporate
Warm Red	#F93822	0	90	86	0	CTA buttons, packaging
Pantone 185 C (approx)	#E4002B	0	100	81	4	Coca-Cola red
Forest Green	#2D572C	75	22	100	15	Eco / organic labels
Sky Blue	#76D7EA	50	0	5	0	Healthcare, tech
Coral	#FF6F61	0	65	55	0	2019 Color of Year
Navy	#003366	100	67	0	44	Finance, luxury
Gold (CMYK safe)	#C5961B	0	25	86	23	Certificates, awards
Skin Tone (light)	#FFCC99	0	20	40	0	Portrait retouching ref
Registration Black	#000000	100	100	100	100	Crop marks only (never fills)
Max Ink Limit (typical)	-	Total ink ≤ 300% - 320%				Prevents ink bleed-through

Frequently Asked Questions

This tool performs a formulaic RGB-to-CMYK conversion without an ICC color profile. Professional prepress uses device-specific profiles (e.g., FOGRA39 for European coated paper, SWOP for US web offset). The mathematical conversion gives a starting point. For color-critical jobs, import the extracted HEX into Adobe Illustrator or similar with your printer's ICC profile applied.

Total Ink Coverage (TIC) is the sum of all four CMYK channels. A pixel with C=80, M=70, Y=60, K=50 has a TIC of 260%. Most offset presses limit TIC to 300% - 320% for coated stock and 240% - 280% for uncoated. Exceeding this causes ink to not dry properly, leading to smearing, set-off, and paper cockling. This tool displays TIC for each extracted color.

The algorithm places all image pixels into a single 3D bounding box in RGB space. It finds the channel (R, G, or B) with the greatest range and splits the box at the median value along that axis. This process repeats recursively until the desired number of color buckets is reached. Each bucket's average color becomes a palette entry. It prioritizes perceptually distinct regions over sheer pixel count.

Yes. Transparent pixels (alpha = 0) are excluded from the quantization. Semi-transparent pixels are composited over white (R=255, G=255, B=255) before conversion, which matches standard print behavior where transparency is flattened to the paper color.

In subtractive color mixing, blue is produced by combining cyan and magenta inks. The formula yields C = (1 - 0 - 0)/(1 - 0) = 1 and M = (1 - 0 - 0)/(1 - 0) = 1, with K = 1 - max(0, 0, 1) = 0. This is mathematically correct. In practice, print shops may add a small K component and reduce C/M to save ink and improve shadow density. This is called GCR (Gray Component Replacement).

The tool processes images up to 20 MB file size. Internally, images larger than 2 megapixels are downscaled proportionally before quantization to maintain responsive UI performance. The color accuracy impact of downscaling is negligible for palette extraction since the algorithm seeks dominant color clusters, not individual pixel precision.