Marina Bloj - Academia.edu (original) (raw)
Papers by Marina Bloj
Colour memory is very important for many activities in our every day life including shopping. In ... more Colour memory is very important for many activities in our every day life including shopping. In this study we investigated whether our ability to remember and identify a colour over a short time was affected by two different factors: display mode and illuminant colour. To evaluate the effect of display mode, colour swatches were presented either as real paper samples or as accurate computer simulations displayed on a calibrated monitor. The colour swatches could be presented under either a 'daylight' illuminant (two intensities, 85 or 50 cd/m2) or a highly artificial purple illuminant (45 cd/m2). For the study we chose 48 colours from the Natural Colour System (NCS) and divided them into three groups: blue, red and yellow. Each group had 2 target colours. Observers memorised the target colours, one per trial, as part of a 16 patch 'reference palette' that was shown for 20 secs. Immediately, this palette was replaced by a 'test palette' containing the target colour among 15 similar distractors and the observers' task was to identify the previously learned colour. The experiment consisted of 36 experimental conditions (2 display modes x 3 illuminants x 6 target colours) resulting in a 3-way repeated measures design. Each experimental condition was tested 3 times for each of our 10 colour normal participants and the order of target colour and illuminant was randomised for each observer, while the display condition was blocked. Analysis of the results revealed that there was no significant effect of display mode or illuminant. Our findings indicate that our short term memory for colour is independent of the nature of the illuminant and equally good for real papers and computer simulations.
When colourimetrically characterising a high dynamic range display (HDR) built from an LCD panel ... more When colourimetrically characterising a high dynamic range display (HDR) built from an LCD panel and an LED backlight one is faced with several problems: the channels may not be constant; they may not be independent and there may be a significant radiant output at the black level. But crucially, colour transforms are underdetermined, which means that the number of colourimetric dimensions is smaller than the number of device channels. While the first three problems are associated with the LCD, the fourth problem stems from the additional channel in the HDR, the backlight.
Proceedings of the 4th symposium on Applied perception in graphics and visualization - APGV '07, 2007
Ten years ago Greenberg and colleagues presented their framework for realistic image synthesis , ... more Ten years ago Greenberg and colleagues presented their framework for realistic image synthesis , aiming "to develop physically based lighting models and perceptually based rendering procedures for computer graphics that will produce synthetic images that are visually and measurably indistinguishable from real-world images", paraphrasing Sutherland's 'ultimate display' . They specifically encouraged vision researchers to use natural, complex and three-dimensional (3D) visual displays to get a better understanding of human vision and to develop more comprehensive visual models for computer graphics that will improve the efficiency of algorithms. In this paper we follow Greenberg et al.'s directive and analyse colour and luminance gradients in a complex 3D scene. The gradients arise from changes in the light source position and orientation of surfaces. Information in image gradients could apprise the visual system about intrinsic surface reflectance properties or extrinsic illumination phenomena, including shading, shadowing and inter-reflections. Colour gradients induced by inter-reflection may play a similar role to that of luminance gradients in shape-from-shading algorithms; it has been shown that 3D shape perception modulates the influence of interreflections on surface colour perception ].
ACM SIGGRAPH 2009 Courses on - SIGGRAPH '09, 2009
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Human Vision and Electronic Imaging XIV, 2009
In the real world we can find large intensity ranges: the ratio from the brightest to the darkest... more In the real world we can find large intensity ranges: the ratio from the brightest to the darkest part of the scene can be of the order of 10000 to 1. Since most of our electronic displays have a limited range of around 100 to 1, the last 20 years has seen much work done to develop different algorithms that compress the actual dynamic range of an image to that available in the display device. These algorithms, known as tone mappers, attempt to preserve as much of the images characteristics as possible . An increasing amount of research has also been done to try to evaluate the 'best' tone mapper. Approaches have included pair wise comparisons of tone mapped images [2], comparison with real scenes [3] or using images displayed on a High Dynamic Range (HDR) monitor . None of these approaches are entirely satisfactory and all suffer from potential confounding factors due to participant's interpretation of instructions and biases.
Handbook of Visual Display Technology, 2012
ABSTRACT In this chapter we present an overview of how we perceive color. We start with an outlin... more ABSTRACT In this chapter we present an overview of how we perceive color. We start with an outline of the physiology of the human visual system and discuss both the trichromatic and color-opponent theories of color vision. We conclude with a description of the phenomenon of color constancy and the factors that contribute to it.
Abstracts Materials & Sensations, 2008
Colour memory is very important for many activities in our every day life including shopping . In... more Colour memory is very important for many activities in our every day life including shopping . In this study we investigated whether our ability to remember and identify a colour over a short time was affected by two diff erent factors: display mode and illuminant colour. To eval uate the effect of display mode, colour swatches were presented either as
IS&T/SID 16th Color Imaging …, 2008
There are a number of problems for which colour-vectors need to be ordered: vector morphology and... more There are a number of problems for which colour-vectors need to be ordered: vector morphology and colour-to-greyscale conversion are two important examples. A lexicographic ordering can perform this function, but while the luminance and saturation ...
Journal of Visual Communication and Image Representation, 2007
When colourimetrically characterising a high dynamic range display (HDR) built from an LCD panel ... more When colourimetrically characterising a high dynamic range display (HDR) built from an LCD panel and an LED backlight one is faced with several problems: the channels may not be constant; they may not be independent and there may be a significant radiant output at the black level. But crucially, colour transforms are underdetermined, which means that the number of colourimetric dimensions is smaller than the number of device channels. While the first three problems are associated with the LCD, the fourth problem stems from the additional channel in the HDR, the backlight.
Journal of Vision, 2011
Abstract A sinusoidal luminance grating can be perceived as a surface with a series of depth corr... more Abstract A sinusoidal luminance grating can be perceived as a surface with a series of depth corrugations. Chromatic information can alter the perceived depth of the corrugations: Kingdom's 'colour-shading effect'. He found that a chromatic sinusoid, orthogonal to a ...
Journal of Vision, 2004
When a planar object is rotated with respect to a directional light source, the reflected luminan... more When a planar object is rotated with respect to a directional light source, the reflected luminance changes. If surface lightness is to be a reliable guide to surface identity, observers must compensate for such changes. To the extent they do, observers are said to be lightness constant. We report data from a lightness matching task that assesses lightness constancy with respect to changes in object slant. On each trial, observers viewed an achromatic standard object and indicated the best match from a palette of 36 grayscale samples. The standard object and the palette were visible simultaneously within an experimental chamber. The chamber illumination was provided from above by a theater stage lamp. The standard objects were uniformly-painted flat cards. Different groups of naïve observers made matches under two sets of instructions. In the Neutral Instructions, observers were asked to match the appearance of the standard and palette sample. In the Paint Instructions, observers were asked to choose the palette sample that was painted the same as the standard. Several broad conclusions may be drawn from the results. First, data for most observers were neither luminance matches nor lightness constant matches. Second, there were large and reliable individual differences. To characterize these, a constancy index was obtained for each observer by comparing how well the data were accounted for by both luminance matching and lightness constancy. The index could take on values between 0 (luminance matching) and 1 (lightness constancy). Individual observer indices ranged between 0.17 and 0.63 with mean 0.40 and median 0.40. An auxiliary slant-matching experiment rules out variation in perceived slant as the source of the individual variability. Third, the effect of instructions was small compared to the inter-observer variability. Implications of the data for models of lightness perception are discussed.
Journal of Vision, 2004
In the companion study , we present data that measure the effect of surface slant on perceived li... more In the companion study , we present data that measure the effect of surface slant on perceived lightness. Observers are neither perfectly lightness constant nor luminance matchers, and there is considerable individual variation in performance. This work develops a parametric model that accounts for how each observer's lightness matches vary as a function of surface slant. The model is derived from consideration of an inverse optics calculation that could achieve constancy. The inverse optics calculation begins with parameters that describe the illumination geometry. If these parameters match those of the physical scene, the calculation achieves constancy. Deviations in the model's parameters from those of the scene predict deviations from constancy. We used numerical search to fit the model to each observer's data. The model accounts for the diverse range of results seen in the experimental data in a unified manner, and examination of its parameters allows interpretation of the data that goes beyond what is possible with the raw data alone.
Journal of Vision, 2010
Chromatic shading on a surface (spatial gradients in colour) may arise from several physical fact... more Chromatic shading on a surface (spatial gradients in colour) may arise from several physical factors, eg: variations in surface pigment concentration, shadows caused by occlusion of a spectrally non-neutral light source, and mutual reflections between surfaces of different spectral ...
Colour memory is very important for many activities in our every day life including shopping. In ... more Colour memory is very important for many activities in our every day life including shopping. In this study we investigated whether our ability to remember and identify a colour over a short time was affected by two different factors: display mode and illuminant colour. To evaluate the effect of display mode, colour swatches were presented either as real paper samples or as accurate computer simulations displayed on a calibrated monitor. The colour swatches could be presented under either a 'daylight' illuminant (two intensities, 85 or 50 cd/m2) or a highly artificial purple illuminant (45 cd/m2). For the study we chose 48 colours from the Natural Colour System (NCS) and divided them into three groups: blue, red and yellow. Each group had 2 target colours. Observers memorised the target colours, one per trial, as part of a 16 patch 'reference palette' that was shown for 20 secs. Immediately, this palette was replaced by a 'test palette' containing the target colour among 15 similar distractors and the observers' task was to identify the previously learned colour. The experiment consisted of 36 experimental conditions (2 display modes x 3 illuminants x 6 target colours) resulting in a 3-way repeated measures design. Each experimental condition was tested 3 times for each of our 10 colour normal participants and the order of target colour and illuminant was randomised for each observer, while the display condition was blocked. Analysis of the results revealed that there was no significant effect of display mode or illuminant. Our findings indicate that our short term memory for colour is independent of the nature of the illuminant and equally good for real papers and computer simulations.
When colourimetrically characterising a high dynamic range display (HDR) built from an LCD panel ... more When colourimetrically characterising a high dynamic range display (HDR) built from an LCD panel and an LED backlight one is faced with several problems: the channels may not be constant; they may not be independent and there may be a significant radiant output at the black level. But crucially, colour transforms are underdetermined, which means that the number of colourimetric dimensions is smaller than the number of device channels. While the first three problems are associated with the LCD, the fourth problem stems from the additional channel in the HDR, the backlight.
Proceedings of the 4th symposium on Applied perception in graphics and visualization - APGV '07, 2007
Ten years ago Greenberg and colleagues presented their framework for realistic image synthesis , ... more Ten years ago Greenberg and colleagues presented their framework for realistic image synthesis , aiming "to develop physically based lighting models and perceptually based rendering procedures for computer graphics that will produce synthetic images that are visually and measurably indistinguishable from real-world images", paraphrasing Sutherland's 'ultimate display' . They specifically encouraged vision researchers to use natural, complex and three-dimensional (3D) visual displays to get a better understanding of human vision and to develop more comprehensive visual models for computer graphics that will improve the efficiency of algorithms. In this paper we follow Greenberg et al.'s directive and analyse colour and luminance gradients in a complex 3D scene. The gradients arise from changes in the light source position and orientation of surfaces. Information in image gradients could apprise the visual system about intrinsic surface reflectance properties or extrinsic illumination phenomena, including shading, shadowing and inter-reflections. Colour gradients induced by inter-reflection may play a similar role to that of luminance gradients in shape-from-shading algorithms; it has been shown that 3D shape perception modulates the influence of interreflections on surface colour perception ].
ACM SIGGRAPH 2009 Courses on - SIGGRAPH '09, 2009
0&▓uÄf╧*ª┘¬b╬l┴****ñ╨╥*π╥*ù≡á╔^¿P╠**SfOriginalFPS**αô**WMFSDKVersion*11.0. 5358.4827*WMFSDKNe... more 0&▓uÄf╧*ª┘¬b╬l┴****ñ╨╥*π╥*ù≡á╔^¿P╠**SfOriginalFPS**αô**WMFSDKVersion*11.0. 5358.4827*WMFSDKNeeded*0.0.0.0000 IsVBR**í▄½îG⌐╧*ÄΣ└ Seh░╢*µ~N]Háu╜>¿╧= ª};û0▓í┬╞╩╞*p∩τ*╕**@l0╡*┐_.⌐╧*Äπ└ SeE**╥╙½║⌐╧*ĵ ...
Human Vision and Electronic Imaging XIV, 2009
In the real world we can find large intensity ranges: the ratio from the brightest to the darkest... more In the real world we can find large intensity ranges: the ratio from the brightest to the darkest part of the scene can be of the order of 10000 to 1. Since most of our electronic displays have a limited range of around 100 to 1, the last 20 years has seen much work done to develop different algorithms that compress the actual dynamic range of an image to that available in the display device. These algorithms, known as tone mappers, attempt to preserve as much of the images characteristics as possible . An increasing amount of research has also been done to try to evaluate the 'best' tone mapper. Approaches have included pair wise comparisons of tone mapped images [2], comparison with real scenes [3] or using images displayed on a High Dynamic Range (HDR) monitor . None of these approaches are entirely satisfactory and all suffer from potential confounding factors due to participant's interpretation of instructions and biases.
Handbook of Visual Display Technology, 2012
ABSTRACT In this chapter we present an overview of how we perceive color. We start with an outlin... more ABSTRACT In this chapter we present an overview of how we perceive color. We start with an outline of the physiology of the human visual system and discuss both the trichromatic and color-opponent theories of color vision. We conclude with a description of the phenomenon of color constancy and the factors that contribute to it.
Abstracts Materials & Sensations, 2008
Colour memory is very important for many activities in our every day life including shopping . In... more Colour memory is very important for many activities in our every day life including shopping . In this study we investigated whether our ability to remember and identify a colour over a short time was affected by two diff erent factors: display mode and illuminant colour. To eval uate the effect of display mode, colour swatches were presented either as
IS&T/SID 16th Color Imaging …, 2008
There are a number of problems for which colour-vectors need to be ordered: vector morphology and... more There are a number of problems for which colour-vectors need to be ordered: vector morphology and colour-to-greyscale conversion are two important examples. A lexicographic ordering can perform this function, but while the luminance and saturation ...
Journal of Visual Communication and Image Representation, 2007
When colourimetrically characterising a high dynamic range display (HDR) built from an LCD panel ... more When colourimetrically characterising a high dynamic range display (HDR) built from an LCD panel and an LED backlight one is faced with several problems: the channels may not be constant; they may not be independent and there may be a significant radiant output at the black level. But crucially, colour transforms are underdetermined, which means that the number of colourimetric dimensions is smaller than the number of device channels. While the first three problems are associated with the LCD, the fourth problem stems from the additional channel in the HDR, the backlight.
Journal of Vision, 2011
Abstract A sinusoidal luminance grating can be perceived as a surface with a series of depth corr... more Abstract A sinusoidal luminance grating can be perceived as a surface with a series of depth corrugations. Chromatic information can alter the perceived depth of the corrugations: Kingdom's 'colour-shading effect'. He found that a chromatic sinusoid, orthogonal to a ...
Journal of Vision, 2004
When a planar object is rotated with respect to a directional light source, the reflected luminan... more When a planar object is rotated with respect to a directional light source, the reflected luminance changes. If surface lightness is to be a reliable guide to surface identity, observers must compensate for such changes. To the extent they do, observers are said to be lightness constant. We report data from a lightness matching task that assesses lightness constancy with respect to changes in object slant. On each trial, observers viewed an achromatic standard object and indicated the best match from a palette of 36 grayscale samples. The standard object and the palette were visible simultaneously within an experimental chamber. The chamber illumination was provided from above by a theater stage lamp. The standard objects were uniformly-painted flat cards. Different groups of naïve observers made matches under two sets of instructions. In the Neutral Instructions, observers were asked to match the appearance of the standard and palette sample. In the Paint Instructions, observers were asked to choose the palette sample that was painted the same as the standard. Several broad conclusions may be drawn from the results. First, data for most observers were neither luminance matches nor lightness constant matches. Second, there were large and reliable individual differences. To characterize these, a constancy index was obtained for each observer by comparing how well the data were accounted for by both luminance matching and lightness constancy. The index could take on values between 0 (luminance matching) and 1 (lightness constancy). Individual observer indices ranged between 0.17 and 0.63 with mean 0.40 and median 0.40. An auxiliary slant-matching experiment rules out variation in perceived slant as the source of the individual variability. Third, the effect of instructions was small compared to the inter-observer variability. Implications of the data for models of lightness perception are discussed.
Journal of Vision, 2004
In the companion study , we present data that measure the effect of surface slant on perceived li... more In the companion study , we present data that measure the effect of surface slant on perceived lightness. Observers are neither perfectly lightness constant nor luminance matchers, and there is considerable individual variation in performance. This work develops a parametric model that accounts for how each observer's lightness matches vary as a function of surface slant. The model is derived from consideration of an inverse optics calculation that could achieve constancy. The inverse optics calculation begins with parameters that describe the illumination geometry. If these parameters match those of the physical scene, the calculation achieves constancy. Deviations in the model's parameters from those of the scene predict deviations from constancy. We used numerical search to fit the model to each observer's data. The model accounts for the diverse range of results seen in the experimental data in a unified manner, and examination of its parameters allows interpretation of the data that goes beyond what is possible with the raw data alone.
Journal of Vision, 2010
Chromatic shading on a surface (spatial gradients in colour) may arise from several physical fact... more Chromatic shading on a surface (spatial gradients in colour) may arise from several physical factors, eg: variations in surface pigment concentration, shadows caused by occlusion of a spectrally non-neutral light source, and mutual reflections between surfaces of different spectral ...