Colour measurements

Various papers - spectral measurements.

These show what proportion of light is reflected from the image at each light wavelength. 400nm corresponds to blue light, 700nm corresponds to red light.

Note that most papers appear to reflect a disproportionate amount of blue light. This makes them seem whiter. Some of the measured blue light is probably a result of fluorescence.

Only one paper shown (Hannemuehle "William Turner") has a neutral (flattish) response across the spectrum. This is a high quality "art" paper for inkjet printing, and when compared to other papers it seems to be yellowish. In reality the other papers are blueish and the Hannemuhle paper is a reasonable almost white colour.

"L" value plotted against RGB values for greyscales.

These measurements were made from various grey coloured patches printed either from dedicated greyscale targets or extracted from the Gretag Macbeth TC 9.18 RGB target set.

A perfect paper/ink combination would produce a smooth curve between (R=G=B)=0 , L=0 and
(R=G=B)=255, L=100. The shape of the curve would be determined by the "gamma" chosen for the reproduction.

A straight line would be a good start!

The "L" value comes from the "L a b" representation of colour, where "L" corresponds to lightness. L=0 is black, L=100 is white. The other two axes, "a" and "b" represent magenta/green and blue/yellow respectively.

The graph above shows reasonably well behaved results above "L" values of 35. Below this point the graphs become very non-linear - which the colour management system aims to correct. (See below)

The matte papers are not capable of producing the darkest blacks (as Ilford Galerie does).  This is partly a result of the fact that the matte surface scatters the light in all directions so the instrument measures the average light reflected whreas a glossy paper produces a simple "specular" reflection which the instrument ignores - in the same way as a real person viewing a glossy print would simply move their viewing angle to eliminate glare from the lights if present.

So the rather poor dark black rendition of the matte papers is not a defect in the paper but an invitable consequence of the matte surface.


Grey scale linearity for Epson 2100 on various papers

Epson R2400 printer.


Matte papers were printed using the Epson Matte Black ink cartridge.
The Hahnemuehle result gives a larger gamut space then the profile downloaded from their website
(HFAr2400WillTurnerPK.icc dated 18-6-2005).

The calibrated result (for Ilford Galerie) shows improvements in the lowest value of L (the darkest blacks) when using Epson ColorBase calibration.
The calibration also linearises the overall response.

Epson 2400 printing 256 patch greyscale.
First graph measured from testchart printed using profile generated by Eye-one Match after calibration with Epson Colorbase utility (measurements using Eye-One Pro)
Second graph shows the same test chart printed as a greyscale (using the three Epson black inks only) after calibration with Epson Colorbase utility (measurements using Eye-One Pro)