Tool
RGB to CMYK Checker
Two tools in one: check whether an image file is really RGB or CMYK by reading its actual file data, convert any colour to an approximate CMYK breakdown, and optionally convert an image to CMYK. The checker and formula converter run in your browser; the real CMYK conversion sends the file to the server for in-memory processing.
Check a file’s colour mode
Reads the file’s actual bytes to tell you if it’s really RGB, CMYK, or grayscale -- not a guess based on how it looks.
Drop an image here, or click to choose one
JPG or PNG give the most reliable result
Approximate colour converter
Pick a colour to see its rough CMYK breakdown. This uses a standard formula, not a press ICC profile, so treat it as a reference point, not a press-accurate value.
C
100%
M
27%
Y
0%
K
22%
RGB 0, 146, 199
Convert an image to real CMYK
A genuine colour-space conversion, not the formula approximation above. This one step needs a server: your file is sent over, converted, and returned as a download. It is processed in memory only and is never saved or stored -- see the privacy policy for details.
Drop an image here, or click to choose one
JPG, PNG, or WEBP · max 15MB
RGB vs CMYK, briefly
Screens create colour by adding light -- red, green, and blue light combined at full strength makes white. Printers create colour by subtracting light with ink -- cyan, magenta, yellow, and black ink combined absorb light and approach black. These are fundamentally different processes, and they don't cover exactly the same range of colours.
In practice, this means some RGB colours -- especially vivid blues, greens, and oranges -- can't be reproduced exactly in CMYK ink and will shift slightly when converted. It's a normal part of the printing process, not a sign of a broken file, but it's worth knowing about before a client sees a colour they didn't expect on a printed proof.
FAQs
What's the difference between RGB and CMYK?
RGB (red, green, blue) is how screens create colour by combining light. CMYK (cyan, magenta, yellow, black) is how most printers create colour by combining ink on paper. The two produce a different range of colours, which is why a bright RGB image can look duller once it's printed in CMYK.
How does the file checker know if an image is really CMYK?
It reads the file's raw bytes directly -- for JPEGs, that means the SOF marker's channel count and the Adobe colour-transform tag, and for PNGs, the colour type stored in the file header. This is different from just looking at the image, since a browser always displays images as RGB regardless of what's stored in the file.
Why can't PNG files be CMYK?
The PNG format was designed for the web and only supports RGB-family colour spaces. If a printer specifically asks for a CMYK file, a PNG will never satisfy that request, whatever colours it looks like it contains.
Is the colour converter's CMYK output accurate for printing?
It's a close approximation using a standard mathematical formula, useful for a rough sense of the ink breakdown. A press-accurate conversion depends on the specific printer, paper stock, and ICC colour profile involved, which this tool doesn't have access to -- your printer's own conversion, or a colour-managed design tool, will be more precise for final production files.
My file is RGB. What should I do before sending it to print?
Many print providers will convert RGB to CMYK automatically, but the colours may shift slightly in the process, especially strong blues, greens, and oranges. If colour accuracy matters for the job, ask your printer whether they'd prefer a CMYK file, or have it converted in a colour-managed tool like Photoshop with their recommended ICC profile.