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Computer processing of remotely sensed images - Mather P.M.

Mather P.M. Computer processing of remotely sensed images - Wiley publishing , 2004. - 350 p.
ISBN 0-470-84918-5
Download (direct link): computerprocessing2004.pdf
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When MIPS starts up, you are asked to agree to the conditions of use (which you can read by pressing the appropriate button), then to nominate a log file into which details of the operations performed during the current session are written. You can read this log file in any ASCII editor, such as Windows Notepad. The MIPS main menu bar is at the top of the screen. The menu names forming the first level in the menu hierarchy are visible (File, View, etc.). The time of day is also displayed (Figure 3.12). The time shown is updated every two seconds unless the computer is working very hard. Clicking on a main menu item produces a sub-menu in the usual way. The functions attached to each menu item are listed in the Help file.
The next few paragraphs are more technical in nature and can be skipped by readers who are not interested in the practical details of computer implementation of software for image processing.
Each image displayed in the main window occupies a ‘child window’ that is owned by the main window in the sense that, for example, minimising the main window will minimise all child windows. Details of the images contained within the child window or windows are stored in a database, so that clone windows can easily be generated to hold derived images that are formed when any image processing operation is executed. Please note that a maximum of eight child windows can be displayed at any given time. The lower toolbar should be kept visible, as it is used to convey information such as the last mouse action (e.g., the word ‘Move’ in Figure 3.12).
In theory, there is no limit in theory to the size of image that can be handled by MIPS, though in practice you will find that memory limitations will mean that very large images are being written to and read from disc, which inevitably slows down operations such as scrolling. As an image is read from a disc file, it is first converted (if necessary) to eight-bit representation, as described in section 3.1, which may affect the contrast and the brightness of an image that has a pixel representation of more than eight bits. The bands chosen for display in red, green and blue are written to separate arrays in computer memory. If greyscale mode is used then the selected single band is copied to all three arrays. The contents of the three arrays are converted to Windows bitmap form and transferred to the graphics memory. Whenever an image is selected, the corresponding data are transferred from the computer’s physical memory (RAM)
74 Hardware and software aspects of digital image processing
Figure 3.12 MIPS main window, showing the menu bar at the top and a child window containing a middle-infrared (Landsat TM band 7) image of the Mississippi River south-west of Memphis, Tennessee (13 January 1983). The word ’move’ on the lower toolbar indicates the last mouse state.
to graphics memory. If the physical RAM is insufficient then the image arrays will be kept in virtual memory. In order to work around the 14 Mb limit on Windows bitmaps, the image is sampled before being transferred from RAM to graphics memory. Scrolling is accomplished by copying the relevant image section into the graphics memory, while zooming uses simple replication of pixels.
3.3.3 Summary of MIPS functions
The functions provided by MIPS are accessed from the main menu bar, shown in Figure 3.12. The menu items are: File, View, Enhance, Filter, Transform, Plot. Classify, Utilities, Graphics, Toolbar, Hyperspectral and Help. The following paragraphs summarise the functions associated with each menu item, and provide a navigational guide to MIPS.
The expanded File Menu is shown in Figure 3.13. Most of the functions relate to the import of image data in various formats, the export of image data, image printing, and INF
file operations, including editing. The most-recently used INF files are listed below the horizontal separator.
The View Menu is shown in Figure 3.14. In alphabetical order, the functions accessed from this menu are: Change Image Scale (i.e. zoom, either continuously or in integral steps), Display Cursor (which provides the coordinates of the mouse cursor plus the pixel values at that point, read from the graphics memory), Display Image (which reads an INF file and allows the user to select either an image or a sub-image for display), and Display RGB Separately. The last of these functions decomposes a colour composite (RGB) image into its three component parts, each of which is shown as a greyscale image.
The Enhance Menu (Figure 3.15) references the modules that implement procedures discussed in Chapters 5 and 6. The first three procedures alter the contrast of the displayed image. The pseudocolour and density slice methods are used to convert a greyscale image into colour representation. The HSI (hue-saturation-intensity) and decorrelation
3.3 Mips software 75
Figure З.1З MIPS File Menu.
Figure 3.15 The MIPS Enhance Menu.
refer to procedures that operate directly on the image itself in order to perform high- or low-pass filter operations. The image minus Laplacian operation adds high-frequency information back to the image, thus sharpening it (section 7.3.2). The Savitzky-Golay technique is either a smoothing operation (low pass) or a high-pass filter, depending on the user’s choice (section The median filter is a low-pass operator, while both the Sobel and Roberts are high-pass filters. The User Defined Filter module allows
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