What can I do with this online tool?

You can convert images (JPG, TIFF, PSD) and PDFs from the CMYK to the RGB color space. CMYK is used for print, RGB for screens, websites and office printers. A PDF keeps its pages, text and vector graphics; only its colors are converted (always to sRGB).

Why does the CMYK profile of my file matter?

CMYK values only say how much of each ink is printed. Which color that gives depends on the press and the paper, and that is what a CMYK profile describes. Most files made for print have their profile embedded (PDF/X files name the profile of the whole document); it is then used for the conversion. For files without one, choose the print standard the file was made for. If you don't know it: in Europe PSO Coated v3 (or its predecessor ISO Coated v2), in the USA GRACoL 2013. Converting without any profile, as many simple converters do, makes images too light and their dark areas gray.

Which RGB profile should I use?

sRGB

The standard for digital images. Browsers, applications and devices are designed for sRGB, and some simply ignore other profiles. If you are not sure, use sRGB.

Adobe RGB (1998)

A widely used working color space for editing images. It has a larger and balanced gamut that can be converted well for many output devices.

ColorMatch RGB

Before Adobe RGB (1998), many used ColorMatch RGB as working space. It was made for Radius' ColorMatch professional monitors. Its gamut is larger than sRGB's, but smaller than Adobe RGB's.

eciRGB v2

The working color space of the European Color Initiative (ECI), similar to Adobe RGB. It is designed for print: it covers the common printing conditions, and its white point and tone curve (L* instead of a gamma) match the print workflow. Also available as ICC v4 profile.

ProPhoto RGB

Also known as ROMM RGB. A very large color space, larger than Adobe RGB, for photographic output. It contains colors that no device can show or print.

PAL/SECAM

Based on the color standards of the European TV industry: a small color space for video.

PRMG RGB

A profile for checking whether image content goes significantly beyond the ICC v4 Perceptual Reference Medium Gamut (more details).

Can I also convert RGB to CMYK?

Not with this service. But our sister websites www.rgb2cmyk.org (images) and www.pdf2cmyk.com (PDFs) convert from RGB to CMYK.