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Chapter 5: Image Processing

To facilitate image processing, JHV can apply a number of standard image processing algorithms similar to thos provided by the popular 'xv' utility. These algorithms are available from the Palette, Image, Filter, and Contour menus. Palette editing is discussed in detail in a later chapter; the other tools are discussed here.

5.1 Image Editing
5.2 Image Filtering
5.3 Image Contour
10 Palette Editor;

Image processing computation may take a long time to complete, depending on the size of the image and the speed of the computer.


5.1 Image Editing

The image menu allows you to modify the data range, change RGB balance in the image, and set the image brightness and contrast, and prepare a negative copy of the image.

Range Modification
RGB Banlance
Brightness/Contrast
Negative
Range Modification
Range Modification allows you to change the range of the data set.

Selecting Range Modification opens a data range dialog box, labeled "New SDS Image Control" in the accompanying illustration. Slide the data range slidebars in the dialog box to specify new maximum and minimum values for the display. Values outside of the range will be set (pinned) to the nearer of the range bounds. Modifying the data range will usually change the color of the image and produce special image effects.

The following figure illustrates range modification of an SDS. The original data range is [202, 21412]; the modified range is [2092, 14692].


Figure 5.1 Modification of image data range
RGB Balance
RGB Balance allows you to adjust the RGB color balance, including the brightness and darkness of component colors. Red, green, and blue can be adjusted synchronously or independently.

Select RGB Balance to open the RGB balance dialog box. The RGB, Red, Green, and Blue slidebars increase the corresponding color values by the selected amount (see below). Each time an adjustment is made, the specified value is added to each image pixel's color value. The maximum resulting value for a color component is 255 and the minimum value is 0; invalid results are truncated. Note that the RGB slidebar adjusts all three colors synchronously.


Figure 5.2 RGB color balance control panel

Changes to pixel RGB values are based on a minimum value of 0 and a maximum value of 255. The indicated percentage increase is a percentage of that maximum value. For instance, assume that a pixel has the value RGB (10, 10, 10) and that you move the Red slidebar to 4% while leaving the other slidebars at 0. This will add 4% of 255, or 10, to the pixel's red component, resulting in a value of RGB (20, 10, 10).

Brightness/Contrast
Brightness/Contrast allows you to adjust the brightness and/or contrast of an image. Contrast is increased by darkening darker pixels and brightening brighter ones and reduced by the reverse process, brightening darker pixels and darkening brighter ones.


Figure 5.3 Image brightness/contrast dialog box

Selecting Brightness/Contrast opens the brightness/contrast dialog box. Select the appropriate channel (Red, Green, Blue, or All), and set the brightness and/or contrast adjustments. Upon completion, click on Preview to view the current changes without terminating the dialog. If you are ready to terminate the dialog, click on Cancel to discard any brightness or contrast changes you have made or Confirm to confirm them.

Negative
Negative transforms a color or grayscale image into its photographic negative by computing the approximate complement of each pixel.

5.2 Image Filtering

JHV provides several filters that let you apply special effects to images. For example, you can smooth or sharpen images, add or reduce noise (change pixel color values by small and random amounts), or emboss and polarize images. You can also produce many interesting visual effects through combined filtering operations. These image filtering algorithms are adapted from the popular xv utility.
Smooth
Sharpen
Add Noise
Find Edge
Flip (Horizontal)
Flip (Vertical)
Emboss
Polarize
Rotate
Smooth
Evens out the noise and small features of an image, thus emphasizing larger features and reducing jagged or uneven edges. (Smooth runs a convolution over each plane (r,g,b) of the image, using an n*n convolution mask consisting of all 1's. This has the effect of replacing each pixel with the average value of all the pixels in the n*n rectangle centered around the pixel in question.)

Sharpen
Highlights edges, lines, and borders. (Sharpen runs an edge-sharpening algorithm on the image, which attempts to maximize contrast between adjacent pixels.)

Add Noise
Adds a small random amount to the color value of each pixel in the image.

Find Edge
Locates horizontal and vertical edges. (Find Edge runs a convolution using a pair of convolutions, one which detects horizontal edges, and one for vertical edges.)

Flip (Horizontal) and Flip (Vertical)
Flips the image horizontally or vertically.

Emboss
Produces a pseudo-3D embossed effect. (Emboss uses a variation of the edge detection algorithm.)

Polarize
Creates a polarized image. (The polarized image is generated through a polar interpretation of the row and column scaling information. The row scale is treated as a set of radius, and the column scale as a set of angle values in the range 0 to 2*PI radians. )

Rotate
Rotates the image 90 degrees counterclockwise.

5.3 Image Contour

The Contour commands create a contour plot from an image. The contour lines are drawn in 3, 5, or 9 levels, which are equally spaced in the range of the data.

Level 3
Level 5
Level 9
The following figure illustrates an image contour. The left image is the original; the right image is a contour plot with level 5.


Figure 5.4 Image contour


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