Visual assessment is the most common clinical investigation of skin reactions in radiotherapy. Due to the subjective nature of this method, additional noninvasive techniques are needed for more accurate evaluation. Our goal is to evaluate the effectiveness of hyperspectral image analysis for that purpose. In this pilot study, we focused on detection and grading of skin Erythema. This paper reports our proposed processing pipeline and experimental findings. Experiments have been performed to demonstrate the efficacy of the proposed approach for (1) reproducing clinical assessments, and (2) outperforming RGB imaging data.
KEYWORDS: Image compression, Image segmentation, Colorimetry, RGB color model, Distortion, Video compression, Visual system, Cones, Human vision and color perception, Video
Instead of de-correlating image luminance from chrominance, some use has been made of using the correlation between
the luminance component of an image and its chromatic components, or the correlation between colour components, for
colour image compression. In one approach, the Green colour channel was taken as a base, and the other colour channels
or their DCT subbands were approximated as polynomial functions of the base inside image windows.
This paper points out that we can do better if we introduce an addressing scheme into the image description such
that similar colours are grouped together spatially. With a Luminance component base, we test several colour spaces and
rearrangement schemes, including segmentation. and settle on a log-geometric-mean colour space. Along with PSNR
versus bits-per-pixel, we found that spatially-keyed s-CIELAB colour error better identifies problem regions. Instead
of segmentation, we found that rearranging on sorted chromatic components has almost equal performance and better
compression. Here, we sort on each of the chromatic components and separately encode windows of each.
The result consists of the original greyscale plane plus the polynomial coefficients of windows of rearranged chromatic
values, which are then quantized. The simplicity of the method produces a fast and simple scheme for colour image and
video compression, with excellent results.
We present here a method that makes use of multispectral image data and generates a novel "photometric-invariant multispectral
image" for this type of data. For RGB, an invariant image has been constructed independent of the colour and
intensity of the illuminant and of shading. To generate this image either a set of calibration images is required, or entropy
information taken from a single image can be used to develop the parameters necessary to produce the invariant.
Nonetheless, generating an invariant image remains a complex and error-prone task for RGB image data. For multispectral
images, we show that photometric-invariant image formation is in essence greatly simplified. One of the requirements
for forming an invariant is the necessity of narrowband-sensor sensors. Here this is the case, and we show that with the
simple knowledge of peak sensor wavelengths we can generate a high-D multispectral invariant. The PSNR is shown to
be high between the respective invariant multispectral features for multispectral images taken under different illumination
conditions, showing lighting invariance for a per-pixel measure; and the s-CIELAB error measure shows that the colour
error between the 3-D colour images used to visualize the output invariant high-D data is also small.
The classical approach to converting colour to greyscale is to code the luminance signal as a grey value image.
However, the problem with this approach is that the detail at equiluminant edges vanishes, and in the worst case
the greyscale reproduction of an equiluminant image is a single uniform grey value. The solution to this problem,
adopted by all algorithms in the field, is to try to code colour difference (or contrast) in the greyscale image. In this
paper we reconsider the Socolinsky and Wolff algorithm for colour to greyscale conversion. This algorithm, which
is the most mathematically elegant, often scores well in preference experiments but can introduce artefacts which
spoil the appearance of the final image. These artefacts are intrinsic to the method and stem from the underlying
approach which computes a greyscale image by a) calculating approximate luminance-type derivatives for the
colour image and b) re-integrating these to obtain a greyscale image. Unfortunately, the sign of the derivative
vector is sometimes unknown on an equiluminant edge and, in the current theory, is set arbitrarily. However,
choosing the wrong sign can lead to unnatural contrast gradients (not apparent in the colour original). Our
contribution is to show how this sign problem can be ameliorated using a generalised definition of luminance and
a Markov relaxation.
In this paper, we present a new method for tracking objects with shadows. Traditional motion-based tracking schemes cannot usually distinguish the shadow from the object itself, and this results in a falsely captured object shape. If we want to utilize the object's shape information for a pattern recognition task, this poses a severe difficulty. In this paper we present a color processing scheme to project the image into an illumination invariant space such that the shadow's effect is greatly attenuated. The optical flow in this projected image together with the original image is used as a
reference for object tracking so that we can extract the real object shape in the tracking process. We present a modified snake model for general video object tracking. A new external force is introduced into the snake equation based on the predictive contour such that the active contour is attracted to a shape similar to the one in the previous video frame. The proposed method can deal with the problem of an object's ceasing movement temporarily, and can also avoid the problem of the snake tracking into the object interior. Global affine motion estimation is applied to eliminate the effect of camera
motion and hence the method can be applied in a general video environment. Experimental results show that the proposed method can track the real object even if there is strong shadow influence.
An image and object search and retrieval algorithm is devised that combines color and spatial information. Spatial characteristics are described in terms of Wiskott’s jets formulation, based on a set of Gabor wavelet functions at varying scales, orientations and locations. Color information is first converted to a form more impervious to illumination color change, reduced to 2D, and encoded in a histogram based on a new stretched chromaticity space for which all bins are populated. An image database of 27,380 images is devised by replicating 2,738 JPEG images by a set of transforms that include resizing, various cropping attacks, JPEG quality changes, aspect ratio alteration, and reducing color to grayscale. Correlation of the complete encode vector is used as the similarity measure. For both searches with the original image as probe within the complete dataset, and with the altered images as probes with the original dataset, the grayscale, the stretched, and the resized images had near-perfect results. The most formidable challenge was found to be images that were cropped both horizontally as well as vertically. The algorithm’s ability to identify objects, as opposed to just images, is tested. In searching for images in a set of 4 classifications, the jets were found to contribute most analytic power when objects with distinctive spatial characteristics were the target.
Recognizing that conspicuous multiple sclerosis (MS) lesions have high intensities in both dual-echo T2 and PD-weighted MR brain images, we show that it is possible to automatically determine a thresholding mechanism to locate conspicuous lesion pixels and also to identify pixels that suffer from reduced intensity due to partial volume effects. To do so, we first transform a T2-PD feature space via a log(T2)- log(T2+PD) remapping. In the feature space, we note that each MR slice, and in fact the whole brain, is approximately transformed into a line structure. Pixels high in both T2 and PD, corresponding to candidate conspicuous lesion pixels, also fall near this line. Therefore we first preprocess images to achieve RF-correction, isolation of the brain, and rescaling of image pixels into the range 0 - 255. Then, following remapping to log space, we find the main linear structure in feature space using a robust estimator that discounts outliers. We first extract the larger conspicuous lesions which do not show partial volume effects by performing a second robust regression for 1D distances along the line. The robust estimator concomitantly produces a threshold for outliers, which we identify with conspicuous lesion pixels in the high region. Finally, we perform a third regression on the conspicuous lesion pixels alone, producing a 2D conspicuous lesion line and confidence interval band. This band can be projected back into the adjacent, non-conspicuous, region to identify tissue pixels which have been subjected to the partial volume effect.
KEYWORDS: RGB color model, Databases, Image segmentation, Data modeling, Light sources and illumination, Image retrieval, Video, 3D modeling, Cameras, Detection and tracking algorithms
Color objects recognition methods that are based on image retrieval algorithms can handle changes of illumination via image normalization, e.g. simple color-channel-normalization or by forming a doubly-stochastic image matrix. However these methods fail if the object sought is surrounded by clutter. Rather than directly trying to find the target, a viable approach is to grow a small number of feature regions called locales. These are defined as a non-disjoint coarse localization based on image tiles. In this paper, locales are grown based on chromaticity, which is more insensitive to illumination change than is color. Using a diagonal model of illumination changes, a least-squares optimization on chromaticity recovers the best set of diagonal coefficients for candidate assignments from model to test locales sorted in a database. If locale centroids are also sorted then, adapting a displacement model to include model locale weights, transformed pose and scale can be recovered. Tests on databases of real images show promising results for objects query.
Many methods for video segmentation rely upon the setting and tuning of thresholds for classifying interframe distances under various difference measures. An approach that has been used with some success has been to establish statistical measures for each new video and identify camera cuts as difference values far from the mean. For this type of strategy the mean and dispersion for some interframe distance measure must be calculated for each new video as a whole. Here we eliminate this statistical characterization step and at the same time allow for segmentation of streaming video by introducing a preprocessing step for illumination-invariance that concomitantly reduces input values to a uniform scale. The preprocessing step provides a solution to the problem that simple changes of illumination in a scene, such as an actor emerging from a shadow, can trigger a false positive transition, no matter whether intensity alone or chrominance is used in a distance measure. Our means of discounting lighting change for color constancy consists of the simple yet effective operation of normalizing each color channel to length 1 (when viewed as a long, length-N vector). We then reduce the dimensionality of color to two-dimensional chromaticity, with values which are in 0..1. Chromaticity histograms can be treated as images, and effectively low-pass filtered by wavelet-based reduction, followed by DCT and zonal coding. This results in an indexing scheme based on only 36 numbers, and lends itself to a binary search approach to transition detection. To this end we examine distributions for intra-clip and inter-clip distances separately, characterizing each using robust statistics, for temporal intervals from 32 frames to 1 frame by powers of 2. Then combining transition and non-transition distributions for each frame internal, we seek the valley between them, again robustly, for each threshold. Using the present method values of precision and recall are increased over previous methods. Moreover, illumination change produces very few false positives.
Photometric stereo (PMS) recovers orientation vectors from a set of graylevel images. Under orthography, when the lights are unknown, and for a single uniform Lambertian surface, one can recover surface normals up to an unknown overall orthogonal transformation. The same situation obtains if, instead of three graylevel images, one uses a single RGB image taken with at least three point or extended colored lights impinging on the surface at once. Then using a robust technique and the constraints among the resulting three effective lighting vectors one can recover effective lights as well as normals, with no unknown rotation. However, in the case of a non-Lambertian object, PMS reduces to the idea of using a lookup table (LUT) based on a calibration sphere. Here, we show that a LUT can also be used in the many-colored- lights paradigm, eliminating the need for three separate images as in standard PMS. As well, we show how to transform a calibration sphere made of a particular material into a theoretical sphere for a cognate material similar in its specular properties but of a different color. In particular, we postulate that a LUT developed from one human's skin can be used for any other person; problems arising from shadows, hair, eyes, etc. are automatically eliminated using robust statistics. Results are shown using both synthetic and real images.
Von Kries adaptation has long been considered a reasonable vehicle for color constancy. Since the color constancy performance attainable via the von Kries rule strongly depends on the spectral response characteristics of the human cones, we consider the possibility of enhancing von Kries performance by constructing new `sensors' as linear combinations of the fixed cone sensitivity functions. We show that if surface reflectances are well-modeled by 3 basis functions and illuminants by 2 basis functions then there exists a set of new sensors for which von Kries adaptation can yield perfect color constancy. These new sensors can (like the cones) be described as long-, medium-, and short-wave sensitive; however, both the new long- and medium-wave sensors have sharpened sensitivities -- their support is more concentrated. The new short-wave sensor remains relatively unchanged. A similar sharpening of cone sensitivities has previously been observed in test and field spectral sensitivities measured for the human eye. We present simulation results demonstrating improved von Kries performance using the new sensors even when the restrictions on the illumination and reflectance are relaxed.
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