G7 is an Idealliance specification that defines a universal appearance for B&W imagery (or a printed grayscale), as well as how to calibrate and control any printing or proofing system to achieve that appearance. It is also the basis of GRACoL and SWOP, and the new CGATS.21 suite of Reference Print Conditions.
G7 uses the same CMYK calibration curves as traditional TVI-based calibration, but with much more valuable results. Unlike TVI calibration, which is unrelated to human vision, G7 is based on visual appearance, achieving the same pictorial qualities of tonality and gray balance across all print technologies. By controlling grays, color images also look as “pleasing” as possible without ICC profiles. For even more accuracy, and color-critical work, G7 should be combined with ICC color management.
In addition to being a specification, G7 also defines a simple method for calibrating CMYK printing devices. Part of the success of G7 is related to the ease of calibration. ISO estimates more than 50,000 printers worldwide implement and maintain G7 based workflows.
By focusing on visual appearance rather than mechanical variables like TVI, G7 offers many benefits.
When used with ISO-standard ink and paper, G7 helps offset printers simulate a GRACoL® or SWOP® proof without a custom press profile.
G7 brings some non-offset printing (e.g. dry-ink digital) close enough to GRACoL or SWOP for certain work. Higher accuracy can be achieved by adding ICC profiles.
An ICC profile made after G7 calibration can have a longer life and achieve higher accuracy than one made without G7
All G7 printing systems have a “shared neutral appearance,” meaning that files prepared for any G7 printer should look pleasing on any other. This has profoundly simplified and improved CMYK file exchange.