Color correcting raster data

Color correction can help render each raster dataset to appear as a single seamless image. It can be applied to an existing raster catalog or a mosaic dataset.

NoteNote:

This topic will focus on color correcting using a raster catalog. To understand the steps to color correct a mosaic dataset, see Color correcting a mosaic dataset.

Two methods can be used to apply a color correction: color balancing and color matching. Color balancing adjusts the contrast and color of each raster dataset to a reference raster. Color matching uses a reference raster dataset to which each of the source raster datasets is matched using one of three methods: statistic match, histogram match, or linear correlation. Color matching consists of two processes: first, the areas of overlap will have the matching calculations determined, then the pixel values will be interpolated for the rest of the raster datasets.

Color correction can be applied to a raster catalog layer or to a mosaicked raster dataset while it is being created.

Color correction can only take place if the following are true about your data:

Pre-color corrected imagesColor corrected images

Pre-stretch

Pre-stretching can be performed on each raster catalog or mosaic dataset item before any other color correction takes place. This means that the original raster catalog item will be using its stretched pixel values, rather than its raw pixel values, in the color correction process. You may want to use this option to change the color to an expected distribution before applying color correction.

For raster catalogs, the Pre-stretching check box becomes available if either the Color Balancing or the Color Matching check box is checked. For mosaic datasets, this option is available on the Mosaic Color Correction window and with the Color Balance Mosaic Dataset tool. There are three pre-stretch methods available:

Color balancing

Color balancing uses one of three techniques to color correct your raster catalog items or mosaic datasets: dodging balancing, histogram balancing, and standard deviation balancing.

The target color surface is only available if the dodging balancing technique is chosen. When using the dodging technique, each pixel needs a target color, which is picked up from the target color surface. There are five types of target color surfaces that you can choose from: single color, color grid, first order surface, second order surface, and third order surface.

The Use Reference Target Image check box allows you to specify the target raster used to balance your raster catalog or mosaic dataset items. If the check box is checked, you can specify the target image. If the check box is not checked, the system will automatically calculate the target.

The Apply Contrast Adjustment check box is used to apply a contrast stretch to your output color correction result. If you check the box, the output will appear sharper, since a contrast stretch will be applied.

Color matching

Color matching matches the overlapping areas between the reference raster and the source rasters. Once the matching algorithm is determined in the overlap areas, it will be applied to the source rasters. Color matching can use one of three methods to interpolate the proper color match from the reference raster to the source rasters (see below).

In addition to the color correction requirements, there are two scenarios where color matching cannot be performed:

NoteNote:

Color matching is not available with mosaic datasets. It is only available with raster catalogs.

The first step in color matching is to determine the reference raster catalog item, either automatically or manually. The overlapped areas between the reference raster and the adjacent source raster datasets undergo the matching method chosen to determine the color transformation that is required. This transformation is applied to all the source rasters, while the raw pixel values of the reference raster is not changed. This procedure continues until all the rasters in the catalog have undergone this color transformation.

The image below shows two raster datasets that are overlapping and have slightly different color. With color matching, you are able to choose one image to match the color of the other image (reference raster). The first step is to choose the reference raster; for this example, the raster dataset outlined in yellow is chosen as the reference raster dataset. The raster dataset outlined in blue will be the source raster dataset, which will match the color of the reference.

pre-color matching

The next step is to color match the areas of overlap. Only the areas where the yellow and blue outlines overlap will undergo the color-matching process. Once the transformation algorithm has been determined, the transformation will take place on the source image; the raw pixel values of the reference raster will not be changed.

post color matching

There are three matching methods for the color matching process:

The reference raster is the raster catalog item (raster dataset) that will not change its raw pixel values. The use of contrast stretching may make the reference raster look different, but the actual values are unchanged. The source raster datasets will conform to the qualities of the reference raster. The reference raster can be automatically chosen by an algorithm, or you can manually choose the reference when using the Layer Properties dialog box.

Related Topics

5/18/2014