Area Dominates Edge in Pointillistic Colour.

["Koenderink J", "van Doorn A", "Gegenfurtner K"]

i-Perception 2018

In Pointillism and Divisionism, artists moved from tonal to chromatic palettes, as Impressionism did before them, and relied on what is often called optical mixture instead of stirring paints together. The so-called optical mixture is actually not an optical mixture, but a mental blend, because the texture of the paint marks is used as a means to stress the picture plane. The touches are intended to remain separately visible. These techniques require novel methods of colour description that have to depart from standard colorimetric conventions. We investigate the distinctiveness of transitions between regions as defined through such artistic techniques. We find that the pointillist edges are not primarily defined by luminance contrast but are achieved in almost purely chromatic ways. A very simple rule suffices to predict transition distinctiveness for pairs of cardinal colours (yellow, green, cyan, blue, magenta, and red); it is simply distance along the colour circle or in the RGB cube. Distinctiveness of partition depends mainly on the colours of the regions, not the sharpness of the transition.

31 Figures Extracted

Figure 1.

Paul Signac (1863–1935), Auxerre, La Rivière (1902–1903). Oil on canvas, height: 55.5 × 46.5 cm, private collection (image in the public domain). At...

Figure 2.

At top, two uniform areas of stripes abut in a nonexistent edge. At centre, two uniform, but mutually different areas are connected by way of a smooth...

Figure 3.

Example of the hard-edge stimulus. On top, the achromatic reference; at bottom, a polychromatic case. The structure of the colour gamuts and the relev...

Figure 4.

Example of the soft-edge stimulus. On top, the achromatic reference; at bottom, a polychromatic case. The structure of the colour gamuts and the relev...

Figure 5.

Schematic examples of hard achromatic edges. Notice that the left and right regions are both nonuniform; yet, the contrast of the overall pattern is w...

Figure 6.

Monochromatic colour samples in the CWK (Ostwald) triangle (see Appendix A). Notice that the distribution is skewed so as to favour saturated colours ...

Figure 7.

Polychromatic hue samples from a triangular distribution (see Appendix A). In this example, the average hue is yellow, and outliers range from red to ...

Figure 8.

The instruction sheet used in the experiment.

Figure 9.

A schematic overview of the stimuli used in each condition. (Impressions of the actual screen images were presented in Figures 3 and 4 .) The colum...

Figure 10.

Paired histograms of the responses over all observers and colour pairs, differentiated with respect to the stimulus categories. Notice that the dichot...

Figure 12.

As Figure 11 ; here, HE–MG stands for “hard-edge, monochromatic gamut.”

Figure 13.

As Figure 11 ; here, SE–PG stands for “soft-edge, polychromatic gamut.”

Figure 11.

Distinctiveness responses are plotted against the median of the distinctiveness response over observers. Original data plotted at left; observers are ...

Figure 14.

As Figure 11 ; here, HE–PG stands for “hard-edge, polychromatic gamut.”

Figure 15.

Some examples of chromatic transition structure. In each case, there is the chromatic transition shown in the bipartite disk at top; below it is an an...

Figure 16.

Array plots of the observations. The response range has been mapped on the full grey scale, where black represents zero and white represents the maxim...

Figure 17.

Overview of the results for pairs of the analogous colours for the case of the soft-edge, monochromatic stimuli. The bars show quartile values of the ...

Figure 18.

Results for the complementary colour pairs for the case of the soft-edge, monochromatic stimuli. The bars show quartile values of the distinctiveness ...

Figure 19.

At top-left, an attempt at an overview of some data for the case of monochromatic, soft-edge stimuli (results for the other cases are quite similar). ...

Figure 23.

Correlations of the predictions of the three models with the observer settings.

Figure 20.

The array plots for the three models. Again, these have been normalised to use the full grey scale, from black (representing zero) to white (represent...

Figure 21.

The median data for the hard-edge, monochromatic gamut case (black bars) compared with the predictions of the RGB cube colour distances (red bars), CI...

Figure 22.

The hard-edge, polychromatic transition at top has zero distinctiveness in the prediction of all three models. Yet, we find it easy enough to see the ...

Figure 24.

Some mutually very different, but equally valid grey-level interpretations of the Signac painting ( Figure 1 ).

Figure 25.

Paul Signac (1890), The Beacons at Saint-Briac, Opus 210 , 65 × 81 cm, oil on canvas (public domain). At left, a hard on top and a soft edge below; b...

Figure B1.

At left, the cases of a transition in a single RGB colour channel with veil in either one of the two remaining RGB colour channels. At right, the case...

Figure B2.

The case of simultaneous edges in all three RGB colour channels, in which case there will be no overlay. Here, the difference is in the polarity of th...

Figure C1.

Normalised data for the hard monochromatic condition as quartiles over observers as bar plots for the various colour pairs. The transition structure...

Figure C2.

Normalised data for the hard polychromatic condition as quartiles over observers as bar plots for the various colour pairs. The transition structure...

Figure C3.

Normalised data for the soft monochromatic condition as quartiles over observers as bar plots for the various colour pairs. The transition structure...

Figure C4.

Normalised data for the soft polychromatic condition as quartiles over observers as bar plots for the various colour pairs. The transition structure...