2012 ICA Mountain Cartography Workshop New Zealand NAGI Fusion Method Aileen Buckley Rajinder Nagi Esri, Redlands, California, USA September 2012
The NAGI Fusion Method
Jan 27, 2015
Integrating a color raster data layer, such as elevation tints, with a grayscale raster layer, such as a hillshade, is an important visualization function in cartography, remote sensing, and geographic information systems (GIS). A number of methods have traditionally been used to integrate these types of rasters. In one approach, the input rasters are combined into a new output raster by transforming the original data using, for example, an intensity, hue, saturation (IHS) transformation. Another approach involves the use of layer transparency, in which one raster is transparently draped over the other. However, both these approaches distort the original colors, and layer transparency has the added problem that gradient detail in the hillshaded raster is suppressed. The optimal solution would be to integrate the color and grayscale rasters while retaining the fidelity of the original data.
In this paper, we introduce a new technique, called the NAGI (No Alteration of Gradient or Intensity) fusion method, to integrate color and grayscale rasters in a manner that preserves the original colors from the color raster while retaining the apparent gradient from the grayscale raster. The NAGI fusion method does not require any code or programming, and no software extensions are required. It can be modified easily to suit the characteristics of the input rasters or the requirements for the output raster. It can be implemented using raster processing techniques introduced in ArcGIS10.0; however, the concepts described can be adapted for use with most cartography, GIS, or remote-sensing software.
The method was tested with a variety of datasets, with rasters of varying resolutions, at a range of spatial extents, with diverse types of thematic content, and with different ArcGIS rendering methods, thus demonstrating the versatility and applicability of the NAGI fusion method.
In this paper, we introduce a new technique, called the NAGI (No Alteration of Gradient or Intensity) fusion method, to integrate color and grayscale rasters in a manner that preserves the original colors from the color raster while retaining the apparent gradient from the grayscale raster. The NAGI fusion method does not require any code or programming, and no software extensions are required. It can be modified easily to suit the characteristics of the input rasters or the requirements for the output raster. It can be implemented using raster processing techniques introduced in ArcGIS10.0; however, the concepts described can be adapted for use with most cartography, GIS, or remote-sensing software.
The method was tested with a variety of datasets, with rasters of varying resolutions, at a range of spatial extents, with diverse types of thematic content, and with different ArcGIS rendering methods, thus demonstrating the versatility and applicability of the NAGI fusion method.
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2012 ICA Mountain Cartography WorkshopNew Zealand
NAGI Fusion MethodAileen Buckley
Rajinder Nagi
Esri, Redlands, California, USA
September 2012
No Alteration of Grayscale or Intensity (NAGI) fusion method
• Rajinder Nagi
• to combine grayscale and colored raster without losing color intensity or hillshade detail
1. a simple mean is calculated from combined input rasters
2. a gamma stretch is applied to the output from the first step
3. a contrast stretch is applied to the output from the second step
(a) elevation tinted DEM, (b) hillshaded DEM, (c) elevation tint overlaid on hillshade with 30% transparency, (d) 50% transparency, and (e) 70% transparency
Transp
arency o
f colo
red im
age
Transparency
(a) hillshade of DEM, (b) elevation tint of DEM, (c) elevation tint overlaid on hillshade with 50% transparency, (d) IHS pan sharpening, (e) Esri pan sharpening, and (f) Brovey pan sharpening
a. b. c.
d. e. f.
Pansharpening
Step 1: Calculate the mean
• a panchromatic image (e.g., hillshade) is added to each of the three bands of a multispectral (RGB) image
• then the mean is calculated
• the panchromatic raster could be a hillshade, black and white aerial image, panchromatic satellite image, etc…
• the multispectral raster could be a thematic layer, such as land cover/land use, soils, geology- in this example, an elevation tint
Step 2: Gamma stretch
• affects the degree of contrast between the midlevel gray values of a raster
• does not affect the black or white values
• the overall brightness of a raster dataset is altered- values greater than 1 – increase the contrast in darker areas
and decrease the contrast in the lighter areas
- values lower than 1 – decrease the contrast in the darker areas and increase the contrast in the lighter areas
• NAGI fusion method: gamma value of 0.5
Step 3: Contrast stretch
• enhances the contrast in an image
• values at the low end of the original histogram are assigned to black and values at the high end are assigned to white
• the remaining values are distributed linearly between the extremes
• NAGI fusion method: minimum-maximum stretch with values of 4 and 104
histograms of (a) hillshade, (b) red band of multispectral RGB image, (c) simple mean, (d) gamma stretch of 0.5, (e) minimum-maximum stretch
a. b.
c. d. e.
Transformations
a. b.
c. d. e.
(a) hillshaded DEM, (b) elevation tinted DEM, (c) elevation tint overlaid on hillshade with 50% transparency, (d) IHS fusion method output, and (e) NAGI fusion method output
In ArcGIS• ETOPO1
• colormap file
• mosaic dataset functions
a. b.
c. d. e.
(a) hillshaded DEM, (b) elevation tinted DEM, (c) elevation tint overlaid on hillshade with 50% transparency, (d) IHS fusion method output, and (e) NAGI fusion method output
In ArcGIS• GTOPO30
• color ramp
• Image Analysisfunctions
a. b.
c. d. e.
(a) hillshade of Mt. Baker DEM, (b) rasterized geology map of Mt. Baker, (c) geology map overlaid on hillshade with 50% transparency, (d) IHS fusion method output, and (e) NAGI fusion method output
In ArcGIS• Elevation Services
• classified renderer
• mosaic dataset functions
To learn more…
• ArcWatch – Esri online monthly newsletter
• Nagi, R. (2012a) Learn a New Method for Displaying Hillshades and Elevation Tints. ArcWatch March 2012 - Tip of the Month. http://www.esri.com/news/arcwatch/0312/learn-a-new-method-for-displaying-hillshades-and-elevation-tints.html Last visited 08/01/2012.
• Nagi, R. (2012b) Using Image Analysis Functions to Display Layer Tints on Hillshades. ArcWatch June 2012 - Tip of the Month. http://www.esri.com/news/arcwatch/0612/using-image-analysis-functions-to-display-layer-tints-on-hillshades.html Last visited 08/01/2012.
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