Quality assessment by region in spot images fused by means dual-tree complex wavelet transform

This work is motivated in providing and evaluating a fusion algorithm of remotely sensed images, i.e. the fusion of a high spatial resolution panchromatic image with a multi-spectral image (also known as pansharpening) using the dual-tree complex wavelet transform (DT-CWT), an effective approach for conducting an analytic and oversampled wavelet transform to reduce aliasing, and in turn reduce shift dependence of the wavelet transform. The proposed scheme includes the definition of a model to establish how information will be extracted from the PAN band and how that information will be injected into the MS bands with low spatial resolution. The approach was applied to Spot 5 images where there are bands falling outside PAN’s spectrum. We propose an optional step in the quality evaluation protocol, which is to study the quality of the merger by regions, where each region represents a specific feature of the image. The results show that DT-CWT based approach offers good spatial quality while retaining the spectral information of original images, case SPOT 5. The additional step facilitates the identification of the most affected regions by the fusion process

Diseño hardware de la transformada wavelet discreta: un análisis de complejidad, precisión y frecuencia de operación

The purpose of this paper is to present a comparative analysis of hardware design of the Discrete Wavelet Transform (DWT) in terms of three design goals: accuracy, hardware cost and operating frequency. Every design should take into account the following facts: method (non-polyphase, polyphase and lifting), topology (multiplier-based and multiplierless-based), structure (conventional or pipelined), and quantization format (floatingpoint, fixed-point, CSD or integer). Since DWT is widely used in several applications (e.g. compression, filtering, coding, pattern recognition among others), selection of adequate parameters plays an important role in the performance of these systems.El propósito de este documento es presentar un análisis comparativo de esquemas hardware de la Transformada Wavelet Discreta, DWT, en términos de tres objetivos de diseño: precisión, complejidad y frecuencia de operación. Cada diseño debe considerar los siguientes aspectos: método (no polifásico, polifásico y lifting), topología (basados en multiplicadores y sin multiplicadores), estructura (convencional o pipeline) y formato de cuantización (punto flotante, punto fijo, CSD o entero). Dado que la DWT es ampliamente utilizada en diversas aplicaciones (por ejemplo en compresión, filtrado, codificación, reconocimiento de patrones, entre otras), la selección adecuada de parámetros de diseño desempeña un papel importante en el diseño de estos sistemas

A new approach to change detection in multispectral images by means of ERGAS index

In this letter, we propose a novel method for unsupervised change detection (CD) in multitemporal Erreur Relative Globale Adimensionnelle de Synthese (ERGAS) satellite images by using the relative dimensionless global error in synthesis index locally. In order to obtain the change image, the index is calculated around a pixel neighborhood (3x3 window) processing simultaneously all the spectral bands available. With the objective of finding the binary change masks, six thresholding methods are selected. A comparison between the proposed method and the change vector analysis method is reported. The accuracy CD showed in the experimental results demonstrates the effectiveness of the proposed method

Automatic Image Segmentation Optimized by Bilateral Filtering

The object-based methodology is one of the most commonly used strategies for processing high spatial resolution images. A prerequisite to object-based image analysis is image segmentation, which is normally defined as the subdivision of an image into separated regions. This study proposes a new image segmentation methodology based on a self-calibrating multi-band region growing approach. Two multispectral aerial images were used in this study. The unsupervised image segmentation approach begins with a first step based on a bidirectional filtering, in order to eliminate noise, smooth the initial image and preserve edges. The results are compared with ones obtained from Definiens Developper software

Pansharpening of High and Medium Resolution Satellite Images Using Bilateral Filtering

We provide and evaluate a fusion algorithm of remotely sensed images, i.e. the fusion of a panchromatic (PAN) image with a multi-spectral (MS) image using bilateral filtering, applied to images of three different sensors: SPOT 5, Landsat ETM+ and Quickbird. To assess the fusion process, we use six quality indexes, that confirm, along with visual analysis, good overall results for the three sensors

Land Cover Mapping by an Optimized Object-Oriented Approach. Case of Study Mediterranean Landscapes

Remote sensing information from spaceborne and airborne platforms continues to provide valuable data for different environmental monitoring applications. In this sense, high spatial resolution im-agery is an important source of information for land cover mapping. For the processing of high spa-tial resolution images, the object-based methodology is one of the most commonly used strategies. However, conventional pixel-based methods, which only use spectral information for land cover classification, are inadequate for classifying this type of images. This research presents a method-ology to characterise Mediterranean land covers in high resolution aerial images by means of an object-oriented approach. It uses a self-calibrating multi-band region growing approach optimised by pre-processing the image with a bilateral filtering. The obtained results show promise in terms of both segmentation quality and computational efficiency

Drought estimation maps by means multidate landsat fused images

The purpose of this paper is to analyze the usefulness of traditional indexes, such as NDVI and NDWI along with a recently proposed index (NDDI) using merged data for multiple dates, with the aim of obtaining drought data to facilitate the analysis for government premises. In this study we have used Landsat 7 ETM+ data for the month of June (2001-2009), which merged to get bands with twice the resolution. The three previous indices were calculated from these new bands, getting in turn drought maps that can enhance the effectiveness of decision making

Comunicación encubierta de imágenes a escala de grises en imágenes a color

This manuscript shows a proposal of covert communication of grayscale images into color images. The main parameter taken into account in the design of the scheme is the transparency of the covert image; meaning that the covert image should be highly similar (perceptually and statistically) to the original color image. Several tests were conducted in order to measure both the transparency of the covert image and the quality of the recovered secret image (i.e. gray image)En este documento se presenta un esquema de comunicación encubierta de imágenes en escala de grises ocultas en imágenes a color. El criterio principal en el diseño del esquema es la transparencia de la imagen encubierta, lo que significa que la imagen final (stego) es altamente similar a la imagen de color original, tanto a nivel visual como a nivel estadístico. Se realizan pruebas para medir la transparencia y la calidad de la imagen a escala de grises recuperada en el receptor. 

Método de ocultamiento de píxeles para esteganografía de imágenes en escala de gris sobre imágenes a color

Steganography is the process of data hiding into a host signal with three main characteristics: imperceptibility, payload and quality of the recovered data. For images, one of the pixel modication methods is the BPHM (Block Pixel Hiding Method) which has good imperceptibility and payload, but it does not ensure the good quality of the recovered secret image. In this paper, we propose an improvement of the BPHM with the purpose to obtain similar results to the well-known QIM (Quantization Index Modulation) method. According to the results, the imperceptibility of the stego image and the quality of the recovered secret image were improved, and then, our results are closer to QIM results.El proceso de ocultar datos secretos dentro de una señal huésped se conoce como esteganografía; sus parámetros de diseño son la imperceptibilidad, la capacidad de ocultamiento y la calidad de los datos recuperados. En el caso de imágenes, uno de los métodos existentes basado en la modicación de los píxeles de la imagen huésped es el denominado BPHM (Block Pixel Hiding Method), el cual presenta una buena imperceptibilidad y alta capacidad de ocultamiento, pero no garantiza la calidad de la imagen secreta recuperada. Este artículo propone un método que mejora los resultados de BPHM basado en la selección de banda y un algoritmo de búsqueda global denominado IPHM (Improved Pixel Hiding Method). De acuerdo a  las simulaciones realizadas, los resultados obtenidos con IPHM son mejores a los obtenidos con BPHM y son similares a uno de los métodos más populares en esteganografía de imágenes conocido como QIM (Quantization Index Modulation)

Evaluation of spectral similarity indices in unsupervised change detection approaches

Unsupervised change detection (UCD) is a subject of Remote Sensing whose objective is to detect the differences between two multi-temporal images. In some cases, spectral similarity indices have been used as the comparison block in algorithms of UCD. The aim of this paper is to show in a quantitative way the performance of four spectral similarity indices in the correct identification of changes. Comparison is performed in terms of precision (overall accuracy and kappa index) over medium and high-resolution images (SPOT-5: Satellite Pour l'Observation de la Terre and Quickbird), with a reference obtained through a post-classification method (based on Support Vector Machines, SVM). The results show dependence on the automatic thresholding technique, as well as on the classes associated with the change.La detección de cambios de forma no-supervisada (UCD) es un área de teledetección, cuyo objetivo consiste en encontrar las diferencias entre dos imágenes multi-temporales. En algunos casos, los índices de similitud espectral son utilizados como bloque de comparación de UCD. El objetivo de este documento consiste en analizar de forma cuantitativa el desempeño de cuatro índices de similitud espectral en la correcta identificación de cambios. La evaluación se realiza en términos de la precisión (mediante la precisión global e índice kappa) utilizando imágenes de media y alta resolución (SPOT-5: Satélite Para la Observación de la Tierra y Quickbird), así como una imagen de cambio de referencia obtenida a través de un método de post-clasificación (basado en Máquinas de Soporte Vectorial, SVM). Los resultados obtenidos presentan dependencia con la técnica automática de umbralización, así como con las clases asociadas con el cambio