The alternating least squares technique for nonuniform intensity color correction

Color correction involves mapping device RGBs to display counterparts or to corresponding XYZs. A popular methodology is to take an image of a color chart and then solve for the best 3 × 3 matrix that maps the RGBs to the corresponding known XYZs. However, this approach fails at times when the intensity of the light varies across the chart. This variation needs to be removed before estimating the correction matrix. This is typically achieved by acquiring an image of a uniform gray chart in the same location, and then dividing the color checker image by the gray-chart image. Of course, taking images of two charts doubles the complexity of color correction. In this article, we present an alternative color correction algorithm that simultaneously estimates the intensity variation and the 3 × 3 transformation matrix from a single image of a color chart. We show that the color correction problem, that is, finding the 3 × 3 correction matrix, can be solved using a simple alternating least-squares procedure. Experiments validate our approach. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 232–242, 201

Slide rule-type color chart predicts reproduced photo tones

Slide rule-type color chart determines the final reproduced gray tones in the production of briefing charts that are photographed in black and white. The chart shows both the color by drafting paint manufacturers name and mixture number, and the gray tone resulting from black and white photographic reproduction

Mobile Munsell Soil Color Chart Berbasis Android Menggunakan Histogram Ruang Citra HVC dengan Klasifikasi KNN

Penentuan warna tanah tidak mudah karena banyaknya jenis tanah dan tingginya tingkat kemiripan warna tanah. Untuk mengatasi kesulitan ini, para praktisi menggunakan suatu buku pedoman warna tanah yaitu Munsell soil color chart (MSCC). Penelitian ini bertujuan mengembangkan aplikasi mobile untuk mengidentifikasi warna tanah dalam menentukan warna mayor tanah sesuai buku MSCC. Aplikasi dibangun menggunakan pemodelan warna HVC dengan komponen warna hue, value, dan chroma. Penelitian ini menekankan klasifikasi untuk warna hue saja. Meskipun demikian, diteliti juga komponen warna value dan chroma. Citra yang digunakan sebagai data latih adalah 259 citra dari buku MSCC yang masing-masing berukuran 1600 piksel. Data warna hue dari setiap piksel ini dianalisis dalam bentuk histogram dan diklasifikasikan dengan KNN. Hasil penelitian menunjukkan bahwa akurasi tertinggi dalam klasifikasi nilai hue adalah 45% pada nilai k = 5. Akurasi mungkin dapat ditingkatkan dengan cara menggunakan data soil color yang sudah tersedia secara online

Evaluation of an Inexpensive Sensor to Measure Soil Color

Soil color determination can be subjective due to environmental conditions and human error. The objectives of this study were to examine the precision of a relatively inexpensive color sensor (NixTM Pro); to compare soil color measurements using this color sensor to human determination by soil science professionals using the standard Munsell Color Chart; and to compare the accuracy of this color sensor to a laboratory standard colorimeter (Konica Minolta CR-400). Sensor measurements were compared to the soil color chart by converting the Nix Pro values to Munsell soil color codes using BabelColor conversion software. Thirty-one Cecil (Fine, kaolinitic, thermic Typic Kanhapludults) soil samples were collected and tested for color. Munsell color codes were converted into cyan, magenta, yellow, and black (CMYK) color values, and the Nix sensor\u27s scan results were tested against predetermined Munsell color values and colorimeter CMYK color values using correlation analysis for all treatments. Nix Pro Color Sensor was precise in soil color determination and it was more accurate than the Munsell Color Chart and comparable to the Konica Minolta CR-400 for both dry and moist soil. The Munsell Color Chart was accurate compared to the Konica Minolta CR-400 in dry soil, but it was less accurate in moist soil. The Nix Pro Color Sensor can be a successful tool to measure soil color in the standard Munsell color codes and this study presents a step-by-step method for converting sensor measurements to the standard Munsell color codes

Color calibration of an RGB camera mounted in front of a microscope with strong color distortion

International audienceThis paper aims at showing that performing color calibration of an RGB camera can be achieved even in the case where the optical system before the camera introduces strong color distortion. In the present case, the optical system is a microscope containing a halogen lamp, with a nonuniform irradiance on the viewed surface. The calibration method proposed in this work is based on an existing method, but it is preceded by a three-step preprocessing of the RGB images aiming at extracting relevant color information from the strongly distorted images, taking especially into account the nonuniform irradiance map and the perturbing texture due to the surface topology of the standard color calibration charts when observed at micrometric scale. The proposed color calibration process consists first in computing the average color of the color-chart patches viewed under the microscope; then computing white balance, gamma correction, and saturation enhancement; and finally applying a third-order polynomial regression color calibration transform. Despite the nonusual conditions for color calibration, fairly good performance is achieved from a 48 patch Lambertian color chart, since an average CIE-94 color difference on the color-chart colors lower than 2.5 units is obtained

Polinomial Kromatik Graf Bunga

In this study, the class of a graph called Flower Graph was discussed. Flower Graph is a special way in a graphic. A graph G is called a flower chart-. This graph will be symbolized by . Then, it is defined by a flower chart-, with the petal to which  in a flower graph-, by -petal removed, for . Flower graphics-: with petal as much as  is denoted by . Chromatic polynomial  is the amount of forms to color the point in graph G with  color, where there are no two points that fit to obtain the same color. In the end, using the reduction theorem, the chromatic polynomial theorem of the Sikel chart and the chromatic polynomial graphic of the chromatic polynomial tree of a flower chart obtained

Real-time Model-based Image Color Correction for Underwater Robots

Recently, a new underwater imaging formation model presented that the coefficients related to the direct and backscatter transmission signals are dependent on the type of water, camera specifications, water depth, and imaging range. This paper proposes an underwater color correction method that integrates this new model on an underwater robot, using information from a pressure depth sensor for water depth and a visual odometry system for estimating scene distance. Experiments were performed with and without a color chart over coral reefs and a shipwreck in the Caribbean. We demonstrate the performance of our proposed method by comparing it with other statistic-, physic-, and learning-based color correction methods. Applications for our proposed method include improved 3D reconstruction and more robust underwater robot navigation.Comment: Accepted at the 2019 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS

Water color and circulation southern Chesapeake Bay, part 1

Satellite imagery from two EREP passes over the Rappahannock Estuary of the Chesapeake region is analyzed to chart colored water types, to delineate color boundaries and define circulatory patterns. Surface observations from boats and helicopters concurrent with Skylab overpass define the distributions of suspended sediment, transparency, temperature, salinity, phytoplankton, color of suspended material and optical ratio. Important features recorded by the imagery are a large-scale turbidity maximum and massive red tide blooms. Water movement is revealed by small-scale mixing patterns and tidal plumes of apparent sediment-laden water. The color patterns broadly reflect the bottom topography and the seaward gradient of suspended material between the river and the bay. Analyses of red, green and natural color photos by microdensitometry demonstrate the utility of charting water color types of potential use for managing estuarine water quality. The Skylab imagery is superior to aerial photography and surface observations for charting water color

A colorimetric investigation of color tolerances

The study was conducted to determine the relationships between a standard color and its visually chosen limits. Commonly, limits or tolerances are communicated to printers using an Allen Tolerance Chart. The Allen Chart, used extensively by package printers, provides a standard of the color to be reproduced along with corresponding light and dark limits. A second form of tolerance chart, used by printers of U. S. Department of Transportation hazardous materials warning labels, provides limits for colors three dimensionally. Both types of tolerance charts were used in this study. Three Department of Transportation tolerance charts were measured spectrophotometrically producing a family of curves for the red, green and blue tolerance charts. The curves were then subjected to Eigenvector analysis to determine the similarity among the tolerances for each color. The results suggest the red and green family of curves are somewhat similar, but very different than the blue. Five hundred five Allen Chart standard colors and their light and dark limits were measured with a small spot colorimeter to determine the relationships between the standard colors and their customer allowed limits. The samples were also subdivided into those representing spot color printing and those representing process color printing. The study suggests the average allowable tolerance for light and dark limits and spot and process color was approximately six C. I . E. L*,a*,b* delta E units. Statistically the resu1ts indicate the light allowable tolerance is greater than the dark tolerance and the process color tolerances are greater than the spot, but for all practical purposes the differences are not significant. The delta E values were also subdivided into their component parts to determine which attribute of color (i.e. hue, chroma and lightness) made up the largest portion of the delta E . These results indicate, for the most part, the delta E values are equally represented by hue, chroma, and lightness

Classification Of Rice Leaf Color Into Leaf Color Chart Using LAB Color Space

Leaf Color Chart (LCC) is a measurement tool that can be used to measure the color intensity of rice leaves. The function of these measurements is to find out how many doses of fertilizer are needed by rice plants. However, readings made by human vision have a high level of subjectivity and risk of error. Therefore we need a method that can minimize errors and the level of subjectivity. One method that can be done is to classify the green color of rice leaves using LAB color space. Rice leaf image taken using a smartphone device is then extracted in RGB format. The color is then converted to LAB color space and then compared to the standard green color in the LCC. The comparison results are then used to classify the colors. The testing results show that the method has the value of accuracy, average precision, and average recall of 54.74%, 54.44%, and 51.16% respectively. Therefore the method can only classify correctly half of the data testing