Exercise 6: Color balancing a raster catalog

Complexity: Beginner Data Requirement: ArcGIS Tutorial Data Setup Data Path: C:\arcgis\ArcTutor\Raster\Data Goal: Color balance the raster datasets within a raster catalog and export to a mosaicked raster dataset.

In this exercise, you will color balance the raster datasets within a raster catalog and create a single raster dataset from the color-balanced raster catalog. This exercise takes you through three color correction options to show you how you can experiment with the options to define the correct color correction for your data.

This exercise does not rely on any previous exercises.

Before you begin, it is assumed that you have installed the tutorial at C:\arcgis\ArcTutor\Raster\Data. If not, make the appropriate path changes throughout this tutorial so it works properly for you.

Start ArcMap

Steps:

1. Start ArcMap by clicking Start > All Programs > ArcGIS > ArcMap 10.
2. Click Cancel on the ArcMap - Getting Started window.

   This window may not open if you've previously opted not to show it.

   Note:

   You will be setting the default map document's geodatabase later in this exercise.

Create a file geodatabase

If you have already created the ImageGDB in another exercise, you can skip this section of steps.

Steps:

1. Click the Catalog window button on the Standard toolbar.

   This opens the Catalog window.

2. In the Location text box, type C:\arcgis\ArcTutor\Raster and press ENTER.

   This location is added to the Catalog tree under the Folders Connection heading.

   If your tutorial data was installed in a different location, alter the path according to your installation location.

3. Right-click the Raster folder and click New > Folder.
4. Name the folder Exercises.
5. Right-click the Exercises folder and click New > File Geodatabase.
6. Rename the new file geodatabase ImageGDB.

Set the default geodatabase

Each map document has a default geodatabase, which is the home location for the spatial content of your map. This location is used for adding datasets and saving resulting datasets created by various editing and geoprocessing operations.

Learn about the default geodatabase

Steps:

1. Right-click the ImageGDB geodatabase in the Catalog window and click Make Default Geodatabase.

Create a new raster catalog

You will be creating an unmanaged raster catalog. This is a raster catalog that contains pointers to the source data instead of loading the raster datasets within.

Steps:

1. Right-click the ImageGDB in the Catalog window and click New > Raster Catalog.

   This opens the Create Raster Catalog tool.

2. Type ColorBalanced in the Raster Catalog Name text box.
3. Click the Coordinate System for Geometry Column button .
4. Click Import.
5. Navigate to C:\ArcGIS\ArcTutor\Raster\Data\Orthos, click the first MrSID file, then click Add.
6. Click OK to close the Spatial Reference Properties dialog box.
7. Click the Raster Management Type drop-down arrow and click UNMANAGED.
8. Click OK on the Create Raster Catalog tool window.

   If the reporter window opens, click Close once the process is complete.

   The ColorBalanced raster catalog is created in the geodatabase and added to the ArcMap table of contents. This is an empty raster catalog. You will be adding raster datasets to it in the next steps.

Add raster datasets to the raster catalog

Steps:

1. Right-click the ColorBalanced raster catalog in the Catalog window and click Load > Load From Workspace.

   This opens the Workspace To Raster Catalog tool.

2. Click the Input Workspace browse button .
3. Navigate to C:\ArcGIS\ArcTutor\Raster\Data\Orthos and click Add.
4. Click OK on the Create Raster Catalog tool window.

   If the reporter window opens, click Close once the process is complete.

5. You may need to click the Full Extent button to view the mosaic dataset.

Color correcting the raster catalog

The color correction is stored within the Layer Properties; therefore, from within that dialog box, you can interactively modify and view the results.

In the following steps, you will try several color correction methods.

Turn off the wireframe

Steps:

1. Set up your display so you can see the raster catalog and the Layer Properties dialog box. It is recommended that you modify the scale of the display to 1:500,000 and pan the display so that the raster catalog is to one side. This way, the Layer Properties dialog box does not cover the raster catalog.
2. Right-click ColorBalanced in the table of contents and click Properties.
3. Click the Display tab.

4. Click the Never show wireframe radio button and click OK.

   The raster catalog will redraw by rendering the rasters and not the wireframe. Now you can see each raster dataset in the raster catalog.

Color matching

Color matching matches the overlapping areas between the reference raster and the source rasters. Color matching is not recommended for this dataset because there is not much overlap. However, you can go though the steps to see how this process is done and see the results.

Steps:

1. Click the Select Features By Geometry button on the Tools toolbar.
2. Click a raster dataset within the raster catalog.

   The selected footprint will be highlighted.
3. Right-click ColorBalanced in the table of contents and click Properties.
4. Click the Color Correction tab.
5. Check Color Matching.
6. Click the Define From Selection radio button.
7. Click Apply.

   You will see this result is very poor. This is because there are almost no overlapping pixels within this raster catalog. Therefore, this method should not be used.

8. Uncheck Color Matching and click Apply.
9. Click OK to close the dialog box.
10. Click the Clear Selected Features button on the Tools toolbar.

Histogram balancing

Histogram balancing changes each of the pixel’s values toward the target histogram. Histogram balancing works best when each raster catalog items have similar histogram distributions.

Steps:

1. Click the Color Correction tab.
2. Check Color Balancing.
3. Click the Balancing Method drop-down and click Histogram Balancing.
4. Click Apply.

   Once the raster catalog redraws, you will see that these results are better than the previous result, but still not correct.

Dodging balancing

When you use dodging, each of the pixel values are changed toward the target color. These values are used to determine the output value for each pixel. When using this method, you must also choose the type of target color surface to use, which will affect what the target color is. Dodging balancing tends to give the best result in most cases.

This final method will be one that provides the best correction for this dataset.

Steps:

1. Click the Balancing Method drop-down arrow and click Dodging Balancing.
2. Click the Target Color Surface Type drop-down arrow and select First Order Surface.
3. Check Apply Contrast Adjustment.
4. Click Apply.

   First the target color surface statistics are calculated, then the color balancing is applied.

5. When the correction is complete, click OK to close the dialog box.

Create a color balanced raster dataset

You can export the raster catalog layer to a raster dataset from the table of contents (as described in the steps below) or you can use the Raster Catalog To Raster Dataset tool and check the Color Balancing check box.

Note:

The process to export to a raster dataset may take some time and can be skipped as part of this exercise.

Steps:

1. Right-click ColorBalanced in the table of contents and click Data > Mosaic Raster Catalog.
2. Click the Location browse button .
3. Navigate to and select the ImageGDB and click Add.
4. Type BalancedImage in the Name text box.
5. Click Save.
6. Click Yes to add the exported raster dataset to ArcMap.

You've now created a single color-balanced raster dataset from many raster datasets using a raster catalog. You can close ArcMap without saving the map document.