ABSTRACT Computational models predict that colour constancy should improve with increasing number... more ABSTRACT Computational models predict that colour constancy should improve with increasing numbers of distinct surface reflectances in a scene. The presence of familiar objects may improve constancy by providing reference surfaces for calibration. Colour constancy may also be optimal for daylight illuminations in which it evolved. To probe these potential influences, we have developed a colour constancy measurement that does not require explicit colour matching between objects or achromatic surface adjustment. Here we measure colour constancy by matching illuminations. We used a tuneable illuminator that emits diffuse, nearly uniform light into an enclosed grey box (h35,w65,d55 cm) containing either a colour checker chart or a banana; participants viewed the scene through a viewport. Target illuminants were taken from the daylight locus and an orthogonal locus with the same correlated colour temperature (CCT). Participants (n = 6) were asked to adjust the illumination in ‘warmer’ or ‘cooler’ directions by using two keys on mobile, black keypad, placed on the box floor; keypresses changed the chromaticity in steps of 1 ΔE along one of the loci, depending on trial block. Participants initially dark adapted for 5 minutes. Each trial began with 10 seconds exposure to the target illumination. A sound signalled an illumination change (to a random chromaticity on the designated locus) and the start of the (untimed) adjustment phase. Accuracy was measured as end-distance from the target illumination in perceptually uniform space. For adjustments along the orthogonal locus, accuracy was higher in the presence of the colour checker chart than the banana, (p <.05). In the presence of the checker, higher accuracy was obtained along the orthogonal than the daylight locus (p = .05). Colour constancy corrections thus seem biased towards the daylight locus, and off-daylight-locus illuminations are corrected for more effectively through multiple reflectances than single familiar objects.
Proceedings of The Royal Society B: Biological Sciences, Nov 22, 1997
Image segmentation is an important early stage in visual processing in which the visual system gr... more Image segmentation is an important early stage in visual processing in which the visual system groups together parts of the image that belong together, prior to or in conjunction with object recognition. Two principal processes may be involved in image segmentation: an edge-based process that uses feature contrasts to mark boundaries of coherent regions, and a region-based process that groups similar features over a larger scale. Earlier, we have shown that motion and colour interact strongly in image segmentation by the human visual system. Here we explore the nature of this interaction in terms of edge- and region-based processes. We measure performance on a region-based colour segmentation task in the presence of distinct types of motion information, in the form of edges and regions which in themselves do not reveal the location of the colour target. The results show that both motion edges and regions may guide the integrative process required for this colour segmentation task. Motion edges appear to act by delimiting areas over which to integrate colour information, whereas motion similarities define primitive surfaces within which colour grouping and segmentation processes are deployed.
If it's a banana, it must be yellow: The role of memory colors in color constancy. Anya C. H... more If it's a banana, it must be yellow: The role of memory colors in color constancy. Anya C. Hurlbert anya.hurlbert{at}ncl.ac.uk 1 and; ...
The ability to discriminate between scenes under different illuminations may provide insight into... more The ability to discriminate between scenes under different illuminations may provide insight into how the visual system represents and perhaps discounts changes in illumination (Pearce et al. 2014). Here we examine whether there is an interaction between sensitivity to illumination changes in different chromatic directions and the chromaticity of the surfaces in the scene. Simulated stimulus scenes were rendered hyperspectrally using RenderToolbox3 and displayed stereoscopically. Each scene was specified as a room covered with rectangular, uniform matte surfaces of widely different colors. Across the three surface ensembles used, the shape and position of surfaces was fixed but their assigned surface reflectance varied. Under simulated illuminant D67, one surface ensemble was roughly 'neutral' in average chromaticity (mean xy: [0.32, 0.35]), while the other two were 'reddish-blue' ([0.36, 0.34]) and 'yellowish-green' ([0.39, 0.42]) relative to it. For each ensemble we measured illumination discrimination thresholds along four different chromatic directions ('blue', 'yellow', 'red' and 'green') using a staircase procedure. The subjects viewed the target scene (simulated illuminant D67) and two comparison scenes - one identical to the target and another rendered under the test illuminant - and judged which of the comparison scenes matched the target. Varying average scene chromaticity had an effect on illumination discrimination thresholds, and that effect was different for different illuminant-change directions. Notably, thresholds for the 'blue' illumination-change direction were higher for the 'yellowish-green' surface ensemble than for the 'neutral' (+5.6∆E) and 'reddish-blue' (+6.1∆E) ensembles, while thresholds for the 'red' illumination change-direction were lowest for the 'reddish-blue' ensemble (-3.7∆E relative to the 'neutral'; -4.1∆E relative to the 'yellowish-green' ensemble). Our results show that characterization of illumination discrimination must take the scene surface ensemble into account, and that the relative discriminability of illumination changes in different chromatic directions is influenced by the average chromaticity of the surface ensemble. Meeting abstract presented at VSS 2015.
By demonstrating that adaptation to a particular face can bias the subsequent perception of famil... more By demonstrating that adaptation to a particular face can bias the subsequent perception of familiar faces, a new study supports the prototype theory of face recognition. These results also suggest that the prototype face is formed by averaging and can change with experience.
Page 1. CV) InD C Technical Report 1154 The Computation of Color DTIC S,-In ELECTE A 90 11 Anya C... more Page 1. CV) InD C Technical Report 1154 The Computation of Color DTIC S,-In ELECTE A 90 11 Anya C. Hurlber MIT Artificial Intelligence Laboratory . .~~~r j:..,,iied "- UtliTT-leaAP Page 2. UNC LASS IF IED REPORT D U TIOf '?-PS*AGE oesREAD INSTRUCTIONS ...
ABSTRACT Computational models predict that colour constancy should improve with increasing number... more ABSTRACT Computational models predict that colour constancy should improve with increasing numbers of distinct surface reflectances in a scene. The presence of familiar objects may improve constancy by providing reference surfaces for calibration. Colour constancy may also be optimal for daylight illuminations in which it evolved. To probe these potential influences, we have developed a colour constancy measurement that does not require explicit colour matching between objects or achromatic surface adjustment. Here we measure colour constancy by matching illuminations. We used a tuneable illuminator that emits diffuse, nearly uniform light into an enclosed grey box (h35,w65,d55 cm) containing either a colour checker chart or a banana; participants viewed the scene through a viewport. Target illuminants were taken from the daylight locus and an orthogonal locus with the same correlated colour temperature (CCT). Participants (n = 6) were asked to adjust the illumination in ‘warmer’ or ‘cooler’ directions by using two keys on mobile, black keypad, placed on the box floor; keypresses changed the chromaticity in steps of 1 ΔE along one of the loci, depending on trial block. Participants initially dark adapted for 5 minutes. Each trial began with 10 seconds exposure to the target illumination. A sound signalled an illumination change (to a random chromaticity on the designated locus) and the start of the (untimed) adjustment phase. Accuracy was measured as end-distance from the target illumination in perceptually uniform space. For adjustments along the orthogonal locus, accuracy was higher in the presence of the colour checker chart than the banana, (p <.05). In the presence of the checker, higher accuracy was obtained along the orthogonal than the daylight locus (p = .05). Colour constancy corrections thus seem biased towards the daylight locus, and off-daylight-locus illuminations are corrected for more effectively through multiple reflectances than single familiar objects.
Proceedings of The Royal Society B: Biological Sciences, Nov 22, 1997
Image segmentation is an important early stage in visual processing in which the visual system gr... more Image segmentation is an important early stage in visual processing in which the visual system groups together parts of the image that belong together, prior to or in conjunction with object recognition. Two principal processes may be involved in image segmentation: an edge-based process that uses feature contrasts to mark boundaries of coherent regions, and a region-based process that groups similar features over a larger scale. Earlier, we have shown that motion and colour interact strongly in image segmentation by the human visual system. Here we explore the nature of this interaction in terms of edge- and region-based processes. We measure performance on a region-based colour segmentation task in the presence of distinct types of motion information, in the form of edges and regions which in themselves do not reveal the location of the colour target. The results show that both motion edges and regions may guide the integrative process required for this colour segmentation task. Motion edges appear to act by delimiting areas over which to integrate colour information, whereas motion similarities define primitive surfaces within which colour grouping and segmentation processes are deployed.
If it's a banana, it must be yellow: The role of memory colors in color constancy. Anya C. H... more If it's a banana, it must be yellow: The role of memory colors in color constancy. Anya C. Hurlbert anya.hurlbert{at}ncl.ac.uk 1 and; ...
The ability to discriminate between scenes under different illuminations may provide insight into... more The ability to discriminate between scenes under different illuminations may provide insight into how the visual system represents and perhaps discounts changes in illumination (Pearce et al. 2014). Here we examine whether there is an interaction between sensitivity to illumination changes in different chromatic directions and the chromaticity of the surfaces in the scene. Simulated stimulus scenes were rendered hyperspectrally using RenderToolbox3 and displayed stereoscopically. Each scene was specified as a room covered with rectangular, uniform matte surfaces of widely different colors. Across the three surface ensembles used, the shape and position of surfaces was fixed but their assigned surface reflectance varied. Under simulated illuminant D67, one surface ensemble was roughly 'neutral' in average chromaticity (mean xy: [0.32, 0.35]), while the other two were 'reddish-blue' ([0.36, 0.34]) and 'yellowish-green' ([0.39, 0.42]) relative to it. For each ensemble we measured illumination discrimination thresholds along four different chromatic directions ('blue', 'yellow', 'red' and 'green') using a staircase procedure. The subjects viewed the target scene (simulated illuminant D67) and two comparison scenes - one identical to the target and another rendered under the test illuminant - and judged which of the comparison scenes matched the target. Varying average scene chromaticity had an effect on illumination discrimination thresholds, and that effect was different for different illuminant-change directions. Notably, thresholds for the 'blue' illumination-change direction were higher for the 'yellowish-green' surface ensemble than for the 'neutral' (+5.6∆E) and 'reddish-blue' (+6.1∆E) ensembles, while thresholds for the 'red' illumination change-direction were lowest for the 'reddish-blue' ensemble (-3.7∆E relative to the 'neutral'; -4.1∆E relative to the 'yellowish-green' ensemble). Our results show that characterization of illumination discrimination must take the scene surface ensemble into account, and that the relative discriminability of illumination changes in different chromatic directions is influenced by the average chromaticity of the surface ensemble. Meeting abstract presented at VSS 2015.
By demonstrating that adaptation to a particular face can bias the subsequent perception of famil... more By demonstrating that adaptation to a particular face can bias the subsequent perception of familiar faces, a new study supports the prototype theory of face recognition. These results also suggest that the prototype face is formed by averaging and can change with experience.
Page 1. CV) InD C Technical Report 1154 The Computation of Color DTIC S,-In ELECTE A 90 11 Anya C... more Page 1. CV) InD C Technical Report 1154 The Computation of Color DTIC S,-In ELECTE A 90 11 Anya C. Hurlber MIT Artificial Intelligence Laboratory . .~~~r j:..,,iied "- UtliTT-leaAP Page 2. UNC LASS IF IED REPORT D U TIOf '?-PS*AGE oesREAD INSTRUCTIONS ...
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