The options available in Advanced Color dialog box depends upon the raster field type. For continuous and classified raster, the Color dialog box looks different. If you open a continuous or imagery raster file, it provides you more options. For a Classified and Image Palette raster, you get Class ID, Class value, and color assigned to each class.
In the following sections we have explored the options available for a Continuous raster.
Color Tool
Select an input raster to apply the color transformation. Select the raster from the Input File drop-down list. The following is an example of a typical raster on which various transformation methods will be used to show the difference in appearance.
Display Mode - Select the display mode you wan to apply on the raster from the drop-down list.
Field, Band - If the input file has multiple fields and bands, select the required field/band from the drop-down list.
Disable Alpha Channel - The Disable Alpha Channel check box lets you control the rendering of alpha channel in your raster data. This option is not available when Display Mode is set to Pseudo Mode.
Color table - Select a color look up table from this drop-down list and apply color to the raster on the current map window.
Reverse Color - Select this check-box if you want to place the inflection points in the input raster file in a reverse order. Applying this transform to your raster file will result in an output, as shown below. Here, the color table BrownBlue is reversed:
Override Null Color - Assign a color to all null cells in the input raster.
Color Transformation Options
Using one of the methods listed in this section, you can change the input raster's quality of display and improve its contrast. In this case, the cell values of an input raster are redistributed over a wider or narrower range of values in an output map. The Transform drop-down list contains the following options:
- Linear - In this stretch method, all cell values of the raster are
re-scaled into new values in the output raster. For example, in any single-band,
grayscale raster, the possible cell values range from 0-255. In practice,
however, not all of these values will appear in the input raster. If in your
input raster, the cell values range from 70-180, the linear stretching method
will bring the minimum input value of 70 to the output value 0, and bring the
maximum input value of 180 to output value 255. All intermediate values will
change accordingly. When the image will be displayed, it will have a better
contrast. For example, applying linear stretching on the above raster will
result in the following file:
- Logarithmic - In this method, the smaller cell values in the raster will be mapped to a wider range of colors. The larger values will be mapped to similar colors. The intermediate values are mapped to a shorter range of colors. The formula for calculating logarithmic stretch depends on the minimum and maximum values specified in the stretch range. Any values in the input raster that are smaller than the specified minimum stretch range value will obtain the same color as the minimum stretch range value. Similarly, any values in the input raster that are larger than the specified maximum stretch range value will obtain the same color as the maximum stretch range value.
- Histogram Equalization - In this method, the values of an raster are converted into a number of output intervals. In doing so, all output intervals will contain equal amount of cells. In other words, Histogram Equalization equalizes the intensity distribution of an image.
- User Defined - The user defined breaks enables you to apply custom coloring to the input raster through a variety of techniques, such as, absolute, percentage, and percentile. As the method changes and the clips/breaks altered, the color distribution will be altered automatically.
If you choose User Defined transform, you can specify the following:
- Breaks Defined in - This drop-down list contains the type of color breaks that you will apply to the input raster such as, absolute, percentage, and percentile. For more information, see.
- Break Options - This drop-down list contains the threshold options you will use to apply the color breaks.
- Intervals - The number of rows and break values.
- Interpolate - Smooth the transitions from one color band to the next.
- Transparent Clip Limits - Select this to render the data falling outside the lower and upper clip limits as transparent. It will make the regions falling outside the cutoff areas as transparent.
- Remap Breaks - Select this to remap according to user defined break.
In this section, you can specify the cutoffs that will define the display of your output raster. The options are:
- Limits Specified As - Select this check-box to create an output raster based on the input raster cell data ranges or percentiles. The options are:
- Absolute - The values of the output raster cells depend on the data range that each input raster cell value falls within. The upper and lower cutoff values will be used to create the output raster whose cell values are equal to the values entered as upper and lower cutoffs.
- Percentage - The output raster will depend on the percentage range that each input raster cell value falls within.
- Percentile - The output raster will depend on the percentile range that each input raster cell value falls within. A percentile is a value on a scale of 100 that represents the percent of a distribution that is equal to or less than the entered value.
Histogram
The Histogram provides an interactive easy-to-use interface to visualize the data ranges and color scheme applied for the selected raster. The Histogram visually represents the color distribution contained in the input raster dataset. The Histogram enables you to instantly view the effects of changes to the raster using the various color methods available.
To view the percent and percentile at any place in the histogram move your cursor over the histogram and it appears in the bottom center of the histogram.
When in Linear, Logarithmic or Histogram Equalization mode, the Histogram is composed of a movable mapping line used to adjust either the min/max clip color values. To move the trend line, a drag handle is docked on both ends of the line. Place your mouse cursor over the handle, hold down the left mouse button and drag the handle to the desired location.
You will also see a table containing cell values, number of cells with a value, density in percentage, and the color associated with cells. For example,
Breaks Table
When you select User Defined from the Data Transform drop-down list, you will see the Breaks Table tab adjacent to the Histogram tab. Depending on the break type and options, the values in a break table get populated. For example,
In the above table, you will see the color breaks based on the number of cells and density for each color gradient.
Load - Click this to load a color interval.
Save as - Click this to save the current color interval applied on the raster.