What is G7?
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 defi nes a simple method for calibrating CMYK printing devices. Part of the success of G7 is related to the ease of calibration. More than 1,500 printers worldwide have received G7 Master status by demonstrating their ability to print to G7.
G7 In Pictures
The illustration below shows what G7 can — and cannot — do. The top three images were produced without any calibration using three different printing technologies: dryink digital, inkjet and offset lithography. The bottom images show that G7 calibration has corrected gray tones and improved colored areas. Saturated colors are still affected by ink differences (which G7 cannot adjust), but without a reference proof, all three bottom images are “pleasing” and it’s hard to say which is “correct.”
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 profi le.
- 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 profi les.
- An ICC profi le 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 fi les prepared for any G7 printer should look pleasing on any other. This has profoundly simplified and improved CMYK fi le exchange.
For more information regarding our G7 certification, contact our location at (920) 289-2361