Gamutvision Print Test
Gamutvision Print Test
Gamutvision Print Test measures several of the key factors that contribute to photographic print quality, including
- Color response, the relationship between pixels in the image file and colors in the print,
- Color gamut, the range of saturated colors a print can reproduce, i.e., the limits of color response,
- Tonal response, the relation between pixels and print density, and
- Dmax, the deepest printable black tone: a very important print quality factor
Gamutvision Print Test. measures these factors from a printed test pattern scanned on a flatbed scanner. No specialized equipment is required. You can observe response irregularities by viewing the test print, but you need to run Print Test to obtain detailed measurements of the print’s color and tonal response.
The essential steps in running Print Test are
- Assign a profile to the test pattern, if needed.
- Print the test pattern, noting (as applicable) the printer, paper, ink, working color space, ICC profile, rendering intent, color engine, and miscellaneous software settings.
- Scan it on a flatbed scanner, preferably one that has been profiled. Best results are obtained by scanning it next to a step chart such as the Kodak Q-13 into a file tagged with Adobe RGB (1998) color space.
- Run Gamutvision Print test.
Color quality is a function of gamut— the range of saturated colors a print can reproduce, as well as overall color response— the relationship between file pixels and print color. Tonal quality is strongly correlated with Dmax— the deepest attainable black tone, as well as the tonal response curve. Prints usually appear weak in the absence of truly deep black tones.
- H = Hue varies from 0 to 1 for the color range R→ Y→ G→ C→ B→ M→ R (horizontally across the image on the right). (0 to 6 is used in the Figures below for clarity.)
- S = Saturation = max(R,G,B)/min(R,G,B). S = 0 for grays; S = 1 for the most saturated colors for a given Lightness value.
- LHSL = Lightness = (max(R,G,B)+min(R,G,B))/2. (The HSL subscript is used to distinguish it from CIELAB L.) L = 0 is pure black; 1 is pure white. The most visually saturated colors occur where LHSL = 0.5.
The key zones are,
- S=1. A square with all possible hues (0 ≤ H ≤ 1) and lightnesses (0 ≤ LHSL ≤ 1), where all colors have maximum saturation (S = 1).
- L=0.5. A rectangular region with all possible hues (0 ≤ H ≤ 1) and saturation levels (0 ≤ S ≤ 1) for middle Lightness (LHSL = 0.5), where colors are most visually saturated.
- Gry. Two identical monochrome tone scales, where pixel levels vary linearly, 0 ≤ {R=G=B} ≤ 1.
The zones labelled K, Gry, and W are uniform black (pixel level = 0), gray (pixel level = 127), and white (pixel level = 255), respectively.