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Grading Principles and Technique
Color is defined technically by three scientific components – the Color (Hue), the Saturation (Chroma) and the Lightness, all of which can be measured by instruments.
Unfortunately, the human eye sees color in quite a different way. The eye can tolerate different levels of color mismatch, depending on the color viewed. For example, the eye is very sensitive to slight changes in blue but can tolerate much larger changes in yellow. The ITL Image Grader grades color in the same way as the customer, namely, by primarily using our eyes, complemented with instrument readings.
As with its color grading, ITL grades a press based on the acceptability of its prints to customers using a methodology combining instrument measurement with visual assessment. This not a simple "how much do you like this print?" - A, B or C. There are so many variables and so much subjectivity in a single point assessment that such scoring would not be repeatable and, more importantly, would not point to corrective actions for the print system.
As with its color grading, ITL grades a press based on the acceptability of its prints to customers using a methodology combining instrument measurement with visual assessment. This not a simple "how much do you like this print?" - A, B or C. There are so many variables and so much subjectivity in a single point assessment that such scoring would not be repeatable and, more importantly, would not point to corrective actions for the print system.
After grading, the attribute scores are rolled up into three category scores: Color, Solids and Lines & Text. The Category scores are rolled up into an overall grade for the press. In some categories, the print builds up points by doing good things, but in more cases, the print accumulates demerits because the customer expects no streaks, smooth solids, real blue skies and neutral neutrals. Thus, some "roll ups" are weighted averages of the attribute grades while others use an adaptive algorithm which penalizes low scores more than it rewards high scores, mimicking our own perceptions of print image quality.
ITL grading is independent of the printing process. Ink jet, electrophotographic, offset and other print technologies exhibit very different micro-structures and must conquer different technical challenges, but a customer's eye steps back and looks at the big picture, not the micro-structure or how the technical challenges were contained. The attribute grading mimics the human eye, and in most cases is a real human eye, in how it looks at images.
ITL attributes and grading avoid specific preferences like gloss, texture and gamut, which are application specific and under the printer's control with ink and paper selection and post treatment.