Publications by Costantino Grana

Background subtraction methods are widely exploited for moving object detection in videos in many applications, such as traffic monitoring, human motion capture, and video surveillance. How to correctly and efficiently model and update the background model and how to deal with shadows are two of the most distinguishing and challenging aspects of such approaches. This work proposes a general-purpose method that combines statistical assumptions with the object-level knowledge of moving objects, apparent objects (ghosts), and shadows acquired in the processing of the previous frames. Pixels belonging to moving objects, ghosts, and shadows are processed differently in order to supply an object-based selective update. The proposed approach exploits color information for both background subtraction and shadow detection to improve object segmentation and background update. The approach proves fast, flexible, and precise in terms of both pixel accuracy and reactivity to background changes.

Background The assessment of colours is essential for the diagnosis of malignant melanoma ( MM), both for pattern analysis on dermoscopic images, and when employing semiquantitative methods. Objectives To develop a computer program for colour assessment in MM images mimicking the human perception of lesion colours, and to compare the automatic colour evaluation with one performed by human observers. Methods A colour palette comprising six colour groups ( black, dark brown, light brown, blue grey, red and white) was created by selecting single colour components inside melanocytic lesion images acquired by means of a digital videomicroscope, and was implemented in the image analysis program. Subsequently, colours were assessed by the computer program on 331 melanocytic lesion images composing our image database, and the results were compared with the evaluation of lesion colours performed by the clinician. Results The black, white and blue - grey colours were more frequently found in MMs than in naevi, both by the clinicians and by the computer. In MM images we observed 4.27 +/- 1.14 colours (mean +/- SD) per lesion, as opposed to 3.22 +/- 0.68 in naevi. The correlation between clinical and computer evaluation of the colours was very good, with a value of 0.781 for overall assessment. Conclusions This innovative method for automatic colour evaluation, reproducing clinical assessment of melanocytic lesion colours, may provide numerical parameters to be employed for computer-aided diagnosis of MM.

The description of the border appears to be an important feature for clinical judgement in dermatoscopy, but it is subjective and can lead to different results depending on the examiners’ experience. In order to provide mathematical descriptors for border regularity and to increase the reproducibility of clinical judgement, a method to quantify border characteristics and to automatically reproduce the B (Border) parameters of the ABCD rule was developed. 331 images of pigmented skin lesions, 113 referring to melanomas and 218 to melanocytic naevi, acquired by a digital videomicroscope with a 20× magnification were studied. Clinical evaluation: for the evaluation of border cut-off, a score ranging to 0 from 8 was attributed to each lesion on the basis of the number of segments with an abrupt edge interruption of the pigmentation. Computer elaboration: after automatic border detection, the skin lesion gradient, defined as the change in lightness values along a 30 pixel long segment centred on the lesion border, expressed as the slope of the curve, was calculated along a 30 pixel segment. Minimum and maximum values and the standard deviation were calculated for the description of border regularity. In order to compare clinical and computer evaluation, the lesion border was divided into 8 segments and a threshold for abrupt border cut-off was set on a visual basis. Melanomas presented more abrupt and inhomogeneous margins in respect of melanocytic naevi. A good correlation between clinical evaluation and computer elaboration was found for the number of borders with an abrupt cut-off (rho = 0.834; P < 0.001). Computerized image analysis appears to be able to numerically describe pigmented skin lesions and to reproduce some aspects of the clinical evaluation. Enabling an objective and reproducible description, it could represent a useful support to clinical diagnosis.

In this paper we propose an approach to indoor environment surveillance and, in particular, to people behaviour control in home automation context. The reference application is a silent and automatic control of the behaviour of people living alone in the house and specially conceived for people with limited autonomy (e.g., elders or disabled people). The aim is to detect dangerous events (such as a person falling down) and to react to these events by establishing a remote connection with low-performance clients, such as PDA (Personal Digital Assistant). To this aim, we propose an integrated server architecture, typically connected in intranet with network cameras, able to segment and track objects of interest; in the case of objects classified as people, the system must also evaluate the people posture and infer possible dangerous situations. Finally, the system is equipped with a specifically designed transcoding server to adapt the video content to PDA requirements (display area and bandwidth) and to the user's requests. The main issues of the proposal are a reliable real-time object detector and tracking module, a simple but effective posture classifier improved by a supervised learning phase, and an high performance transcoding inspired on MPEG-4 object-level standard, tailored to PDA. Results on different video sequences and performance analysis are discussed.

Although an improvement of the diagnostic accuracy of pigmented skin lesions (PSL) has been achieved by the epiluminescence technique (ELM), the interpretation of ELM criteria is often confusing, especially for inexperienced observers. To enhance the reproducibility and accuracy of clinical judgement and the training of inexperienced operators, programs for PSL image analysis and algorithms for automatic diagnosis have been developed. The aim of our study was to develop a new program for PSL image analysis, able to describe different aspects of PSLs and to test its descriptive capability on PSL acquired by means of a digital videomicroscope (VMS 110A, Scalar Mitsubishi, Japan) using 20-fold magnification. After automatic border identification and baricentre determination, some geometric parameters, describing shape characteristics of the lesion, were calculated. A mathematical description of the border cut-off was obtained. The texture of the lesion was calculated applying the co-occurrence matrix at different image resolutions. Dark areas and colour areas, referring to selected colour groups, were obtained and their aspect and distribution were mathematically defined and calculated. 281 common nevi and 117 melanomas were numerically described by our program and the capability of the mathematical parameters to distinguish between benign and malignant lesion was tested by means of discriminant analysis. Significant differences were observed for most parameters between different PSL populations. The automatic classification enabled the distinction between melanomas and nevi with a 100% sensitivity and a 82.9% specificity.

Image analysis tools are spreading in dermatology since the introduction of dermoscopy (epiluminescence microscopy), in the effort of algorithmically reproducing clinical evaluations. Color-based region segmentation of skin lesions is one of the key steps for correctly collecting statistics that can help clinicians in their diagnosis. Nevertheless, an efficient and accurate region segmentation algorithm has not been proposed in the literatureyet. This work proposes an iterative fuzzy c-means clustering algorithm based on PCA with the Karhunen-Loève transform of the color space. A topological tree is provided to store the mutual inclusions of the regions and then used to summarize the structural properties of the skin lesion. Preliminary experimental results are presented and discussed.

In this paper we define a Topological Tree (TT) as a knowledge representation method that aims to describe important visual and spatial features of image regions, namely the color similarity, the inclusion and the spatial adjacency. The topological tree exhibits some interesting properties that can be exploited to extract knowledge from images for information retrieval, image understanding and diagnosis purposes. Examples of applications in dermatology are described. The TT can be constructed after segmentation, by computing the spatial relationships of regions or can be generated directly during the segmentation: to this aim we present a novel recursive fuzzy c-means (FCM) clustering algorithm based on the Principal Component Analysis of the color space. The recursive FCM proves to be effective for underlining the adjacency and inclusion property of regions.

In this work we present a transcoding framework and an object-based technique to adapt live and stored videos to the user bandwidth and resources capabilities.Multiple transcoding policies are reviewed and a performance evaluation metric based on the Weighted Mean Square Error that allows different classes of relevance is presented.We present results for different transcoding policies and for different bandwidth requirements, showing that the use of semantic can improve the bandwidth to distortion ratio.

This work presents a general-purpose method for moving visual object segmentation in videos and discusses results attained on sequences of PETS2002 datasets. The proposed approach, called Sakbot, exploits color and motion information to detect objects, shadows and ghosts, i.e. foreground objects with apparent motion. The method is based on background suppression in the color space. The main peculiarity of the approach is the exploitation of motion and shadow information to selectively update the background, improving the statistical background model with the knowledge of detected objects. The approach is able to detect Moving Visual Objects (MVOs), and stopped objects too, since the motion status is maintained at the level of tracking module. HSV color space is exploited for shadow detection in order to enhance both segmentation and background update. Time measures and precision performance analysis in tracking and counting people is provided for surveillance and monitoring purposes.

Clinical evaluation of pigmented skin lesion images is subjective and can lead to different results depending on the examiner’s experience, also applying semiquantitative methods such as the ABCD rule for dermatoscopy. In order to increase the reproducibility of clinical judgement, a method to automatically reproduce the A (Asymmetry) and the B (Border) parameters of the ABCD rule was developed. One hundred and fourteen images of melanomas acquired by a digital videomicroscope with a 20x magnification were studied.Clinical evaluation: a clinical judgement of asymmetry of the shape and pigment distribution along 2 axes were performed by 0–2 scoring system. For the evaluation of the border cut-off, a score ranging to 0 from 8 was attributed to each lesion on the basis of the number of segments with an abrupt edge interruption of the pigmentation. Computer elaboration: after automatic border detection, major and minor axes were obtained and ‘shape asymmetry’ on each axis was calculated considering the proportion of overlapping pixels. A correspondence lower than 90% was selected as the threshold for asymmetry. The ‘pigment distribution asymmetry’ on each axis was calculated comparing the portion of the dark area, obtained by the median cut algorithm, in the two halves of the lesion. A correspondence lower than 80% was considered as the threshold for asymmetry. In order to numerically describe the gradient at the border, the lesion border was divided into 8 segments and the change in lightness values along a 30 pixel long segment centered on the lesion border, expressed as the slope of the curve, was considered. Threshold for abrupt border cut-off was set by a slope greater than 3.609Results: a good correlation between clinical evaluation and computer elaboration was found for shape asymmetry (rho=0.698;p<0.001), pigment distribution asymmetry (rho=0.428;p<0.001) and number of borders with an abrupt cut-off (rho=0.834;p<0.001).