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Thus, when x, y, and the amplitude val- ues of f are all finite, discrete quantities, we call the image a digital image. We use two principal ways in this book to represent digital images.
Assume that an image f x, y is sampled so that the resulting image has M rows and N columns. The values of the coordinates are discrete quantities. For notational clarity and convenience, we use integer values for these discrete coordinates. The notation 0, 1 is used to signify the second sample along the first row.
It does not mean that these are the actual values of physical coordinates when the image was sampled. Figure 2. Note that x ranges from 0 to M - 1 and y from 0 to N - 1 in integer increments. The coordinate convention used in the Image Processing Toolbox to denote arrays is different from the preceding paragraph in two minor ways. First, in- stead of using x, y , the toolbox uses the notation r, c to indicate rows and columns. Note, however, that the order of coordinates is the same as the order discussed in the previous paragraph, in the sense that the first element of a coordinate tuple, a, b , refers to a row and the second to a column.
Image Processing Toolbox documentation refers to the coordinates in Fig. Less frequently, the toolbox also employs another coordinate convention, called spatial coordinates, that uses x to refer to columns and y to refers to rows. This is the opposite of our use of variables x and y. Each element of this array is called an image element, picture element, pixel, or pel.
The terms image and pixel are used throughout the rest of our discussions to denote a digital image and its elements. Clearly, the two representations are identical, except for the shift in origin. Typically, we use the letters M and N, respectively, to denote the number of rows and columns in a matrix.
Variables must begin with a letter and contain only letters, numerals, and underscores. We use conventional Roman, italic notation, such as f x, y , for mathematical ex- pressions.
Recall from Section 1. Note the semicolon ; use of single quotes ' to delimit the string filename. When, as in the preceding command line, no path information is included In Windows, directories in filename, imread reads the file from the Current Directory and, if that are called folders.
The simplest way to read an image from a specified directory is to include a full or relative path to that directory in filename. Table 2. PBM Portable Bitmap. That is, this command gives the number of rows in f. The second dimension of an array is in the horizontal direction, so the state- ment size f, 2 gives the number of columns in f.
The whos function displays additional information about an array. A semicolon at the end of a whos line has no effect, so normally one is not used. Using the syntax number of other syntax forms for performing tasks such as controlling imshow f, [low high] image magnification. Consult the help page for imshow for additional displays as black all values less than or equal to low, and as white all values details. The values in between are displayed as interme- diate intensity values.
Finally, the syntax imshow f, [ ] sets variable low to the minimum value of array f and high to its maximum value. This form of imshow is useful for displaying images that have a low dynamic range or that have positive and negative values. Note the figure number on the top, left of the window. In most of the examples throughout the book, only the images themselves are shown. Note the various pull-down menus and utility buttons.
They are used for processes such as scaling, saving, and exporting the contents of the display window. In particular, the Edit menu has functions for editing and formatting the contents before they are printed or saved to disk. Note that more than one command can be written on a figure window. Typing line, provided that different commands are delimited by commas or semico- figure n forces figure number n to become lons.
As mentioned earlier, a semicolon is used whenever it is desired to sup- visible. Finally, suppose that we have just read an image, h, and find that using imshow h produces the image in Fig.
The improvement is apparent. To start the Image Tool, use the imtool function. Original image courtesy of Dr. David R. Pickens, Vanderbilt University Medical Center. The large, central window is the main view. The Measure Distance tool is in use, showing that the distance between the two pixels enclosed by the small boxes is The Overview Window, on the left side of Fig.
The Main Window view can be adjusted by dragging the rectangle in the Overview Window. The Pixel Region Window shows individual pixels from the small square region on the upper right tip of the rose, zoomed large enough to see the actual pixel values. In addition to the these tools, the Main and Overview Win- dow toolbars provide controls for tasks such as image zooming, panning, and scrolling.
Pixel Region Superimposes pixel values on a zoomed-in pixel view. Distance Measures the distance between two pixels. Image Information Displays information about images and image files. Adjust Contrast Adjusts the contrast of the displayed image. Crop Image Defines a crop region and crops the image. Display Range Shows the display range of the image data. Overview Shows the currently visible image.
Alternatively, the desired format can be specified explicitly with a third in- put argument. This syntax is useful when the desired file does not use one of the recognized file extensions.
For example, the following command writes f to a TIFF file called patient A more general imwrite syntax applicable only to JPEG images is imwrite f, 'filename.
In order to function imfinfo. See Example 2. Figures 2. In order to get an idea of the compression achieved and to obtain other image file details, we can use function imfinfo, which has the syntax imfinfo filename imfinfo where filename is the file name of the image stored on disk. The number of bytes in the original image is com- puted by multiplying Width by Height by BitDepth and dividing the result by 8. The result is This compression ratio was achieved while main- taining image quality consistent with the requirements of the application.
In addition to the obvious advantages in storage space, this reduction allows the transmission of approximately 35 times the amount of uncompressed data per unit time. The information fields displayed by imfinfo can be captured into a so- called structure variable that can be used for subsequent computations. Using Structures are discussed in Section the preceding image as an example, and letting K denote the structure variable, 2.
For example, the image height and width are now stored in structure fields K. Height and K. As an illustration, consider the following use of structure variable K to compute the compression ratio for bubbles The first was to type imfinfo bubbles To learn more about These two different ways of calling imfinfo are an example of command- command function duality, consult the help function duality, an important concept that is explained in more detail in the page on this topic.
A more general imwrite syntax applicable only to tif images has the form There images only , and 'fax4'. For example, if the image dimensions are in inches, colres is the number of dots pixels per inch dpi in the vertical direction, and similarly for rowres in the horizontal direction. As this digital image processing by gonzalez 3rd edition free download, it ends happening visceral one of the favored ebook digital image processing by gonzalez 3rd edition free download collections that we have.
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