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.

1. 2012 ICA Mountain Cartography
Workshop
New Zealand
September 2012
NAGI Fusion Method
Aileen Buckley
Rajinder Nagi
Esri, Redlands, California, USA

2. 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

9. Transparency
(a) elevation tinted DEM, (b) hillshaded DEM, (c) elevation
tint overlaid on hillshade with 30% transparency, (d) 50%
transparency, and (e) 70% transparency

10. Pansharpening
a.
b.
c.
d.
e.
f.
(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

11. 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

12. 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

13. 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

14. Transformations
c.
a.
b.
d.
e.
histograms of (a) hillshade, (b) red band of multispectral RGB
image, (c) simple mean, (d) gamma stretch of 0.5, (e)
minimum-maximum stretch

15. •
e.
colormap file
•
b.
ETOPO1
•
a.
d.
In ArcGIS
mosaic dataset
functions
c.
(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

16. •
e.
color ramp
•
b.
GTOPO30
•
a.
d.
In ArcGIS
Image Analysis
functions
c.
(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

17. •
e.
classified renderer
•
b.
Elevation Services
•
a.
d.
In ArcGIS
mosaic dataset
functions
c.
(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

18. 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-newmethod-for-displaying-hillshades-and-elevationtints.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-imageanalysis-functions-to-display-layer-tints-onhillshades.html Last visited 08/01/2012.