Browsing by Author "Dejmek, Petr"

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    Calibrated color measurements of agricultural foods using image analysis
    (ELSEVIER, 2006) Mendoza, Fernando; Dejmek, Petr; Aguilera, Jose M.
    A computer vision system (CVS) was implemented to quantify standard color of fruit and vegetables in sRGB, HSV and L*a*b* color spaces, and image capture conditions affecting the results were evaluated. These three color spaces are compared in terms of their suitability for color quantification in curved surfaces. The results show that sRGB standard (linear signals) was efficient to define the mapping between R'G'B' (no-linear signals) from the CCD camera and a device-independent system such as CIE XYZ. The CVS showed to be robust to changes in sample orientation, resolution, and zoom. However, the measured average color was shown to be significantly affected by the properties of the background and by the surface curvature and gloss. Thus all average color results should be interpreted with caution. L*a*b* system is suggested as the best color space for quantification in foods with curved surfaces. (C) 2006 Elsevier B.V. All rights reserved.
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    Colour and image texture analysis in classification of commercial potato chips
    (ELSEVIER, 2007) Mendoza, Fernando; Dejmek, Petr; Aguilera, Jose M.
    The images of commercial potato chips were evaluated for various colour and textural features to characterize and classify the appearance and to model the quality preferences of a group of consumers. Features derived from the image texture contained better information than colour features to discriminate both the quality categories of chips and consumers' preferences. Entropy of a* and V and energy of b* from imaees of the total chip surface, average and variance of H and correlation of V from the images of spots and/or defects (if they are present). and average of L* from clean images (chips free of spots and/or defects) showed the best correspondence with the four proposed appearance quality groups (A: 'pale chips', B: 'slightly dark chips, C: 'chips with brown spots', and D: 'chips with natural defects'), giving classification rates of 95.8% for training data and 90% for validation data when linear discriminant analysis (LDA) was used as a selection criterion. The inclusion of independent colour and textural features from images of brown spots and/or defects and their clean regions of chips improved the resolution of the classification model and in particular to predict 'chips with natural defects'. Consumers' preferences showed that in spite of the 'moderate' agreement among raters (Kappa-value = 0.51), textural features have potential to model consumer behaviour in the respect of visual preferences of potato chips. A stepwise logistic regression model was able to explain 86.2% of the preferences variability when classified into acceptable and non-acccptable chips. (c) 2007 Elsevier Ltd. All rights reserved.
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    Gloss measurements of raw agricultural products using image analysis
    (ELSEVIER, 2010) Mendoza, Fernando; Dejmek, Petr; Aguilera, Jose M.
    Gloss is considered one of the most important visual attributes of many foods, which is difficult to measure objectively. In this paper, a gloss imaging system (GIS) was implemented to evaluate the suitability of four indexes for measuring gloss from intensity images in flat and curved surfaces and to analyze gloss of some fruits and vegetables. Three indexes were computed from goniometric curves: maximum intensity (MI), width of the curve at 50% (WC), and area under the curve (AC). The fourth index was computed from the same intensity images as the average of the reflected luminance flux (LF) at the surface of the image. The results showed linear relationships (R-2 = 0.97) when values of MI, AC, LF for flat and curved gloss targets in the range of 4-90 units of gloss (GU) were compared with their standard gloss levels. However, the measured gloss was significantly affected by curvature and unevenness of the surface of fruits and vegetables. In spite of this, we concluded that a colour digital camera of moderate cost combined with simple image analysis procedure can yield parameters which correlate highly with the gloss appearance of fruits and vegetables and allow measurements over a very wide range of gloss with high sensitivity. (C) 2009 Elsevier Ltd. All rights reserved.
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    Soaking in a NaCl solution produce paler potato chips
    (ELSEVIER, 2007) Santis, Nathalie; Mendoza, Fernando; Moyano, Pedro; Pedreschi, Franco; Dejmek, Petr
    Pairs of potato slices were blanched, soaked in a NaCl solution or water and fried. The originally adjoining faces of the chips were analysed for average L*a*b* color by digital photography and image analysis.