What is eciRGB 1.0 .icc profile and why should I care?

Posted: September 24, 2012 in Color, ECI, ECI RGB, FOGRA, ICC, ICC profile, ISO 12647-2, ISO Press standardisation, PCS
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ECI RGB gamut compared with offset printing gamut

eciRGB 1.0 is recommended by the European Color Initiative (ECI) for use as an RGB working color space and color data exchange format for ad agencies, publishers, reproduction and printing houses.

There are a couple of aspects that led to the development and release of eciRGB by the ECI in 1999: – Up to Adobe Photoshop 5.5 the default for the working color space was the monitor profile of the computer on which Photoshop was running. This turned out to be a less than perfect approach, as every computer may have a different monitor profile, and a working color space should not depend on what happens to be the monitor profile on a given computer, but should always be the same, at least within any given workflow.

Furthermore a monitor profile typically does not cover certain ranges of colors that can easily be produced on a printing press – the major area of weakness of a monitor compared with a press is in the Cyan color region. – Staying in the scanner profile’s color space often makes no sense, as a scanner’s color space typically is not very uniform (a characteristic offered for example by the Lab color space) this makes them unsuitable for any corrections or editing.

Lab in principle looked like a good alternative candidate, but hardly any widely used software (until maybe very recently) supported editing and retouching for 16 bit Lab data or import of 16 bit Lab images (and while PostScript/EPS supports up to 12 bit Lab data, in PDF 16 bit image data have only been introduced very recently in version 1.5, earlier versions only accommodating a maximum of 8 bit), and 8 bit Lab data was far too inefficient, as only less than a third of all possible Lab color values actually occur in real world color data: which means that out of the 8 bit only a bit more than 6 bit would actually be used, which simply isn’t enough.

Even with 16 bit Lab the issue arises that it uses twice the amount of data – while the increase in file size often will be moderate due to compression, the amount of RAM needed definitely doubles. – while there were and still are other reasonable offerings around in terms of RGB working space ICC profiles ECI wanted to see one that … has a gamut that covers all colors that can be printed on today’s printing presses – whether sheet fed or web offset, gravure or newsprint – but not much beyond (in order to not to waste precision for bits that never really get used) … produces a neutral gray whenever the values for Red, Green and Blue are equal … offers equidistance, i.e. equal difference between two color values in eciRGB mirrors an perceived equal difference when these colors are seen by the human eye … is based on a Gamma of 1.8 and a light source of 5000K. This profile was created and tested in 1998 and provided to the public free of charge in early 1999. Most ECI members have meanwhile based their internal workflows on eciRGB as the preferred (and often the only) RGB working color space, and have been more than satisfied with the advantages achieved.

Is eciRGB the only working color space that makes sense? Definitely no. Other experts and user groups in the industry as well as vendors have been working on this issue and have come up with alternative options that may work as well as eciRGB. If you happen to have been working with let’s say Adobe RGB or ColorMatch RGB until now, it would not be a good reason to convert your image database to eciRGB just for the sake of then having eciRGB data. Nevertheless, when you are about to set up a new print oriented workflow, the ECI is confident that there are hardly better options than eciRGB (though possibly quite a few that are comparably good).

How does eciRGB compare to sRGB? sRGB has seen excessively wide use, as especially HP and Microsoft were promoting it as the standard RGB profile (in the end often going so far that they – whether directly or indirectly – propose not to use any ICC profiles anymore but instead to simply implicitly store and exchange any RGB data as sRGB. More and more digital cameras, low end inkjet printers and even monitors now simply assume sRGB.

While this may look like a smart move, it must not be forgotten, that sRGB as a color space has serious weaknesses – there are a lot of colors today’s printing presses as well as other output devices like photo printers, large format printers and many inkjets (not to speak of up to date monitors or digital cameras) can produce that cannot be stored in sRGB. If quality is important, sRGB is not an option.

Should I get rid of my scanner profiles right away and use eciRGB instead? No, definitely not. Simply assigning eciRGB instead of the specific profile e.g. for a scanner is one of the worst things you can do. Always use the correct source profile for the data at hand, and then convert from that color space into eciRGB.

Note 1: What’s a working color space anyway? The short answer is, that such a color space is good for working on an image (or rather any color object), whether color correcting or retouching it or editing it in any other way. A working color space can be made such that it is independent of idiosyncrasies of a specific device (e.g. it can be made uniform to preserve detail equally well in each area of the color space). At the same time it can be made such that it serves a class of color spaces well, e.g. that it comprises all or most of the colors that can be output with all monitor and printing devices that are available today.

Note 2: In ISO there is currently work underway – as ISO standard “ISO/CD 22028-2 Photography and graphic technology – Extended colour encodings for digital image storage, manipulation and interchange – Part 2: Reference Output Medium Metric RGB colour image encoding (ROMM RGB)” – to possibly arrive at a working color space that is even better than eciRGB or other widely used working color spaces.

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Comments
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