Select Raster Layer as the current layer in Layer Manager, and Grid Parameters setting options will appear in the Layer Properties interface. It contains the functional controls of Raster Layer's Property Settings, such as brightness, contrast, color table, specified grid value style, grid function, etc.

Grid Parameters

Special Value Setting

• Special value: You can click the pick button to pick a pixel value in the Image Layer of Map and set it as a special value (snap is supported), or you can directly enter a value in the value box as a special value. That is, users need to set the Display Effects of grid pixels with certain values.
• Special Value Style: The label is used to set the display color of the specified grid value. Click the Drop-down Button on the right side of the Special Value Style: tab, and select a color in the pop-up color panel, and the pixel of the grid value will be displayed as the specified color.
• Special Value Transparent Display: The check box is used to set whether the specified grid value is Transparent Display. Check this box to set the specified grid value pixel to Transparent Display; uncheck this box to still display the specified grid value color in the specified color.

Background value setting

You can Replace the Color of the specified background value pixel to Other Color.

• Background value: You can click the pick button to pick a pixel value Set as background value in the Image Layer of Map (capturing is supported), or you can directly enter a value in the value box as the background value.
• Transparent background value: Click the Drop-down Button to set the replacement color in the pop-up color panel.

Transparent color setting

Transparent color setting is used to set a certain Color Setting in Raster Layer as transparent color, that is, to set the Area Setting covered by the specified color in Raster Data as transparent effect. To set the transparent color, you need to use the Transparent Color and Transparent Color Tolerance commands together.

• Transparent color: Select this check box to set the designated pixel with no value as Transparent Display; uncheck this item to display the designated pixel with no value in the designated color.
• Transparent Color Tolerance: After setting the transparent color tolerance, assume that the original Color Settings is (R, G, B) and the Tolerance Settings is a. The required Transparent Display color range is between (r-a, g-a, b-a) and (R + a, G + a, B + a).

Brightness

When the current layer is a Raster Layer, the Brightness spin box is used to adjust the brightness of the Raster Layer. You can adjust the brightness of the current layer by directly entering the brightness value in the Brightness spin box. Or click the Brightness spin box and use the mouse slider to adjust the brightness to view the settings in real time.

Contrast

When the current layer is a Raster Layer, the Contrast spin box adjusts the contrast of the Raster Layer. You can adjust the contrast of the current layer by directly entering the contrast value in the Contrast spin box. Or click the right of the Contrast number adjustment box and use the mouse slider to adjust the contrast to view the setting results in real time.

Interpolation mode

When zooming and browsing Raster Data, you need to map the Original Image to a larger or smaller set of pixels, and SuperMap provides five interpolation methods. Nearest Neighbor, Low Quality, High Quality, High Quality Double Linear Interpolation, High Quality Cubic Interpolation. Different interpolation methods determine the quality of the grid display, but the higher the display quality of the output image, the longer it takes.

• Nearest Neighbor: a simpler interpolation method that is faster to process, but has the worst Display Effects.
• Low Quality: This method performs a pre-filter to ensure high quality shrinkage, and the enlarged display quality of the interpolated image is poor.
• High Quality: The image display quality is high when zooming, but the output image takes a long time.
• High Quality Dual Linear Interpolation: Performs a pre-filter to ensure high quality Display Effects for scaled grids with the specified high quality dual Linear interpolation method.
• High Quality Bi-cubic: Performs a pre-filter to ensure high-quality Display Effects for scaled grids, using the specified High Quality Bi-cubic method. This outputs the highest display quality image.

Grid function

Some analysis processing methods are applied to Raster Data by means of raster functions. When accessing and viewing Raster Data, these functions will be dynamically applied to Raster Data. Therefore, the results of these analysis processing operations can be quickly displayed; However, it takes a long time to process these tasks through the corresponding analysis method, and it will also produce a huge processing result file.

Currently, Application provides five grid function settings: 3D Hillshade Map, Orthophoto 3D Image, Slope Map, Aspect Map, and Viewshed (only available in iDesktopX). It is convenient to quickly browse 3D shading effect, orthophoto effect, slope map, slope direction map and Viewshed without thematic analysis. As shown in the figure below, the Display Effects are obtained by DEM Data Settings different grid functions for a certain area.

Figure: Source DEMRaster Data	Image: Orthophoto 3D Image	Figure: 3D Hillshade Map	Figure: Slope map	Figure: Slope direction diagram	Figure: Viewshed

• None: No raster function is applied. You will not be able to set the light source azimuth, light source elevation angle, and elevation scaling factor.
• Orthophoto 3D Image: The digital differential correction technology is used to obtain the reasonable sunshine intensity of the current point through the elevation of the surrounding adjacent grids, and to correct the image of Raster Data. By default, the light azimuth, light elevation, and elevation scaling factor cannot be set.
• 3D Hillshade Map: 3D shading effect is generated by considering the angle and shadow of the grid surface illumination source. 3D Hillshade Map is a grid map that reflects the relief of the terrain by simulating the shadow of the actual surface. The gray value of each pixel is obtained by using the imaginary light source to illuminate the map and combining with the Slope Aspect information obtained by Raster Data. The gray value of the slope facing the light source is the highest, and the gray value of the slope facing away from the light source is lower, which is the shadow area, thus vividly representing the actual landform and topography of the grid. Because the mountain shadow map calculated by Raster Data has a very realistic three-dimensional effect, it is called 3D Hillshade Map. When 3D Hillshade Map is selected for the Grid Parameters, the light source azimuth angle is set to 315 degrees, the light source elevation angle is set to 45 degrees, and the elevation scaling factor is set to 1 by default.
• Slope Map: Generate a slope map for the DEM Raster Data. By default, the system sets the azimuth angle of the light source to 315 degrees, the elevation angle of the light source to 90 degrees, and the elevation scaling factor to 1.
• Aspect: Generates an aspect for the DEM Raster Data. By default, the azimuth angle of the light source is 360 degrees, the elevation angle of the light source is 45 degrees, and the elevation scaling factor is 1.
• Light Source Azimuth: The light source azimuth is used to determine the direction of the light source and is expressed by an angle. As shown in the figure below, start with the due north direction as 0 degrees, measure clockwise, and assign angle values to each direction from 0 degrees to 360 degrees, so the due north direction is also 360 degrees. It is 90 degrees due east, 180 degrees due south, and 270 degrees due west. The default value for azimuth is 315 degrees.
• Light source elevation angle: The light source elevation angle is the inclination angle when the light source is illuminated, ranging from 0 degrees to 90 degrees. As shown in the figure, when the light source elevation angle is 90 degrees, the light source is perpendicular to the ground surface. The elevation angle defaults to 45 degrees.

  When the azimuth angle of the light source is 315 degrees and the elevation angle is 45 degrees, the relative position between the light source and the surface is shown in the following figure.

• Elevation Scaling Factor: When the unit of the terrain grid value (i.e. elevation value) is different from the unit of the X and Y coordinates, it is usually necessary to multiply the elevation value by an elevation scaling factor to make the three units consistent. For example, the units in the X and Y directions are meters, and the units in the Z direction are feet. Since 1 foot equals 0.3048 meters, you need to specify a scaling factor of 0.3048. If set to 1, there is no scaling. The Projected Coordinate System (in meters) is the

  recommended data for analysis. If you choose to run the analysis in a spherical coordinate system, you need to specify an appropriate Z-factor for the latitude. If the X, Y units are latitude and longitude and the Z unit is the meter, some appropriate Z factors listed in the following table may be used:

   Latitude Z-factor 0 0.00000898 10 0.00000912 20 0.00000956 30 0.00001036 40 0.00001171 50 0.00001395 60 0.00001792 70 0.00002619 80 0.00005156  

• Viewshed: It is the viewable area range map of a certain observation point. The viewable area is generated by picking or setting the observation height and viewing angle range of the point. The default viewing range is 360 degrees.
  • X coordinate value: longitude of the observation point.
  • Y coordinate value: The latitude of the observation point.
  • Elevation Value: The elevation value of the observation point.
  • Visual area value: the color of the current visual area, which is set by the grid value in the color table.

     

  • Start Angle: The starting angle of the observation point, in degrees, starting from 0 degrees in the north direction and increasing in degrees in the clockwise direction. The default Start Angle is 0.
  • Viewing Angle: the observation angle of the observation point result, in degrees, starting from 0 degrees in the north direction and increasing clockwise. The default Viewing Angle is 360.

Display Method

Two display methods, Combination Mode and Stretch Mode, are provided. The Stretch Mode can set the Color Scheme and Stretch method.

Stretch method provides the following: Minimum Maximum, Standard Deviation, Histogram Equalization, Histogram Specification, Gaussian and Percent Clip.

The Stretch method of Batch Settings Raster Layer is supported. In Layer Manager, select multiple Raster layers. Uniform Settings Stretch method in the Layer Properties panel for uniform adjustment of the image Display Effects.

Stretch method

• No stretching: The image is not stretched, but this absolute no stretching is actually only valid for Image Data of unsigned integer 8-bit Storage Format. As shown in the figure below, the left figure shows that the unsigned integer 8-bit image is not stretched, and the image is dark. The right figure shows the histogram of Red Band, and the pixel display values are concentrated in the lower gray level area.

  Figure: No Stretch and Histogram

• Minimum Maximum: Linear stretch of the maximum and minimum values. In this way, the minimum value and the maximum value of the pixel value are used as the range value range, and Linear stretch is performed to make the pixel value distributed between 0, 255. Through this stretching process, the contrast and brightness of the image are significantly improved, so that the objects in the image will be easier to identify. It is generally suitable for stretching Raster Image with dense pixel value distribution.

  As shown in the figure below, the left figure is the result of stretching. The image becomes clearer than that without stretching, and the contrast of the image is enhanced. The right figure is the histogram before stretching in gray, and the histogram after stretching in red.

  Figure: Minimum Maximum and Before and After Stretch Histogram

• Standard Deviation: Increase the contrast of the image by trimming the extreme values of the image and then performing Linear stretch on the other pixel values. The statistics of Original Image data is mainly to obtain the value range of One Standard Deviation, and then according to the Recalculate standard deviation range of Standard Deviation coefficient, Perform Linear stretch on the values within the final calculated standard deviation range, so that they are distributed between 0, 255, and the deviation between the stretched pixel display value and the average value is reduced.

  Standard deviation: The arithmetic square root of the variance, reflecting the degree of dispersion among individuals within a group. Simply speaking, it indicates the degree of deviation between most values and the average value in the group. The larger the standard deviation, the more the majority of the values in the group deviate from the mean. The smaller the standard deviation is, it means that most values in the group are close to the average value.

  As shown in the figure below, the pixel value of the One Standard Deviation coefficient accounts for 68%, and the pixel value of the two Standard deviation coefficient accounts for 95%. The proportion of Three Standard Deviations coefficient pixels is 99%. Standard deviation coefficient is defined as 2. Then the pixel values that exceed 2 standard deviations will be pushed to 0 or 255. Pixel values between Two Standard Deviations are Linear stretch to 0-255. Standard Deviation is often used to lighten a Raster Dataset that has a darker hue.

  The following describes the Stretch method of standard deviation through a histogram. As shown in the figure below, the left figure is the effect of the image after Standard Deviation, and the right figure is the histogram comparison chart before and after stretching. It can be seen that after stretching, the histogram shape of the image conforms to a normal distribution curve, and the standard deviation of the histogram of the stretched image increases. That is, the deviation between the pixel display value of Image Data and the average value is reduced.

  Standard Deviation is often used to lighten darker images.

  Figure: Standard deviation stretching and histogram before and after stretching

• Gaussian: The purpose is to make the pixel values of Image Data tend to be normally distributed. Gaussian belongs to Linear stretch.
  • Gaussian coefficient: The pixel value of the image is multiplied by the coefficient and then stretched to the 0,255 interval.
  • Using Median: If "Using Median" is checked, Gaussian is performed with the pixel median as the central axis during Image Stretching; if it is not checked, Gaussian is performed with the pixel maximum as the central axis by default.
• Percent Clip: In general, it can be assumed that most of the pixels in Image Data are within the upper and lower bounds. Pixel values outside the range can be pushed to both ends by setting the percentage. Linear stretch is then performed on the pixel values within the range. This Stretch method excludes some pixels in the small value part and some pixels in the large value part of the histogram from the stretch, and the remaining part is stretched by the Minimum Maximum method. When using, you need to set the exclusion ratio of the minimum value and the maximum value. The Stretch Display

  can be set individually for each band of the multiband Image Data by clicking the Histogram button to the right of the combo box to open the histogram for each band and specify the minimum and maximum percentage values to be excluded from the stretch. Represents the percentage of pixels in the small portion and the percentage of pixels in the large portion that need to be excluded from the stretch.

  For example, if the value range of an image pixel is 0, 100, and the minimum and maximum exclusion ratios are defined as 10, the application of Percent Clip "will stretch the values between 10, 90 to 0, 255, and 0, 10 will be displayed as 0. 90, 100 is shown to be 255.

  As shown in the figure below, the first figure shows the Display Effects and the histogram without setting the stretching range. From the histogram, it can be seen that there are fewer pixels in the small and large value areas, which affects the contrast of the image and makes the image unclear. If these pixels are excluded from the stretching, The contrast and sharpness of the image can be increased. The second image below shows the effect of a percent truncation of only the stretch settings range after setting the stretch range to exclude pixels at both ends.

  Figure 1: Do not set the stretch range	Figure 2: Setting the Stretch Range

• Histogram Equalization: It belongs to the histogram correction method, which is essentially to perform Non-Linear stretch on the image. By redistributing the pixel values of the image, the number of the pixels in a certain gray scale range is approximately equal, so that the contrast of the peak part in the middle of the original histogram is enhanced, and the contrast of the valley parts on the two side is reduced, so that the histogram of the output image is a flat segmented histogram, and the contrast of the image is enhanced.

  Figure: Histogram of images before and after equalization (image source network)

  Figure: Histogram Equalization Stretch and Histogram Before and After Stretch

  After Histogram Equalization stretching, the overall contrast of the image is strong. The essence of histogram equalization is to reduce the gray level of the image in exchange for the expansion of contrast. So sometimes when we need some grayscale image information, the information may be lost after conversion. When the quality of the original remote sensing data is relatively poor, the dynamic range of the data is small, and the Histogram Distribution is extremely uneven, the histogram equalization enhancement operation is carried out, and the transformed image has a worse sense of hierarchy and is more likely to lose information.

• Histogram Specification: It is a mathematical transformation of the image lookup table to make the histogram of one image similar to that of another image. Histogram Specification is often used as the pre-processing work of adjacent image stitching or dynamic change research using multi-temporal Remote Sensing Imagery; The Histogram Specification allows you to partially eliminate differences in the effect of adjacent images due to solar elevation or atmospheric effects.

  Histogram Specification is similar to Histogram Equalization, except that the Output Result of Histogram Equalization is a fixed, more balanced image. The result of the Histogram Specification is to import a histogram XML file and display the image using the histogram specified by the new histogram file.

Stretch factor

Setting the Stretch Factor is supported only when you select the stretch method as Standard Deviation "or Gaussian.

• Standard Deviation Factor: This parameter is available only when Stretch method is Standard Deviation. The Standard Deviation coefficient determines the range of values for the standard deviation. Assuming that the Standard Deviation range is a, B and the Standard Deviation coefficient is n, the Standard Deviation range is a-n, b+n. The default Standard Deviation coefficient of Application is 2, that is, 2 times of standard deviation is used for stretching by default.
• Gaussian coefficient: This parameter is available only when Stretch method is Gaussian. Assuming that the pixel value range of Image Data is a, B and the Gaussian coefficient is n, when Gaussian is performed, the central axis is kept unchanged, the pixel value is stretched by n times, and finally displayed in the range of 0, 255. The default Gaussian coefficient for the Application is 2.

As shown in the figure below, Figure 1 shows the image Display Effects without any processing. The overall tone is dark, which is not conducive to distinguishing the feature information. However, after stretching (as shown in Figure 2), the image contrast is enhanced, and many feature features are highlighted.

Figure 1: Original Image	Figure 2: Image after stretching

Sets the color table

When the current layer is a Raster Layer, the Settings.. button can be used to set the color of pixels in the Raster Layer in the map. Click the Settings.. button to pop up the Edit Color Table dialog box. The user can set the Color Scheme of Raster Layer through the Edit Color Table dialog box, or set the color used by a pixel value; or adjust the color display scheme of Raster Data by adding new pixel values or deleting some pixel values. For more information, see: Use and Description of the Color Table Settings Dialog Box.

Automatic interpolation of the color chart

Automatic interpolation of the color chart resamples Raster Data to optimize grid cell boundaries for smoother grid color effects.

Figure 1: Uncheck Automatic interpolation of the color chart	Figure 2: Check Automatic interpolation of the color chart

Gamma

The Gamma parameter can be used to adjust the nonlinear brightness and contrast of the grid, so as to enhance the display details of the image and improve the display quality of Raster Data. Values range from 0 to 10 inclusive. Numerical Precision is two decimal places.

• When the Gamma value is equal to 1, the image is not Gamma corrected.
• When the Gamma value is greater than 1, the contrast of the dark area of the image increases and the details are more prominent, but the details of the bright area will be lost and the overall image will become brighter, as shown in Figure 2.
• When the Gamma value is less than 1, the contrast of the bright area of the image increases and the details are more prominent, but the details of the dark area will be lost and the overall image will be darker.

Figure 1: Gamma = 1	Figure 2: Gamma = 2

Related Topics

Set Layer Common Properties

Set Vector Layer Properties

Set Image Layer Properties