Tillie Doyle
Pan sharpening is a radiometric transformation that fuses a multispectral image with a higher-resolution panchromatic image to enhance the spatial resolution of the former. ArcGIS offers several methods to achieve this, including the Brovey transformation, the Esri pan-sharpening transformation, the Gram-Schmidt spectral sharpening method, and more. This process involves creating raster objects, applying filters, and adjusting properties to improve the visualization of the multispectral image. The result is a sharper, more detailed image with enhanced spatial resolution.
| Characteristics | Values |
|---|---|
| What is pan sharpening? | The process of fusing two images together, a multispectral image and a higher-resolution panchromatic image, to achieve higher spatial resolution in the multispectral image. |
| How to pan sharpen an image in ArcGIS | Use the Pan-sharpen button on the Image Analysis window, or modify the layer properties. |
| Steps to sharpen an image | 1. Add the lower-resolution colour image to the map using the Add Data button. 2. Right-click the raster layer in the table of contents and click Properties. 3. Click the Symbology tab. 4. Click RGB Composite on the Show menu. 5. Scroll to the bottom of the Properties list and check Pan-sharpening. 6. Click the Panchromatic Image drop-down arrow and click an image name or click the browse button and select the higher-resolution image. 7. Click the Pan-sharpening Type drop-down list and choose the desired colour transformation. 8. Optionally, type a weight value for each of the red, green, blue, and infrared bands. 9. If the fourth band of your raster dataset is the infrared band and you want to use it, check the 4th-band as Infrared Image checkbox. |
| Image fusion methods | 1. Brovey transformation. 2. Esri pan sharpening transformation. 3. Gram-Schmidt spectral sharpening method. 4. Intensity, hue, saturation (IHS) transformation. 5. Simple mean transformation. |
| Suggested weights for common sensors | Red: 0.166, Green: 0.167, Blue: 0.167, Infrared: 0.5 |
| Tips | It is a good idea to set the display resampling to bilinear interpolation to make the output pan-sharpened image less pixelated. |
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What You'll Learn
Using the Pan-sharpen button
To pan-sharpen an image in ArcGIS, you can use the Pan-sharpen button on the Image Analysis window. This process increases the spatial resolution of a multiband image using a high-resolution, single-band image.
- Open the Image Analysis window in ArcGIS.
- Hold the CTRL key and click on a panchromatic raster layer in the window.
- Click on the Pan-sharpen button.
- A pan-sharpened image will be added to the display as a temporary raster layer.
- If you wish to save this image, select it in the Image Analysis window and click the Export button.
There are several image fusion methods available to create the pan-sharpened image, including the Brovey transformation, Esri pan-sharpening transformation, Gram-Schmidt spectral sharpening method, intensity, hue, saturation (IHS) transformation, and simple mean transformation.
The choice of method depends on the specific requirements of the image analysis. Each method uses different models to improve spatial resolution while maintaining colour accuracy, and some allow for the inclusion of a fourth band, such as a near-infrared band.
By following these steps and selecting the appropriate image fusion method, you can effectively use the Pan-sharpen button to enhance the resolution and visualisation of your images in ArcGIS.
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Modifying layer properties
To pan-sharpen an image in ArcGIS, you can modify the layer properties of a raster layer. Here's a step-by-step guide on how to do this:
First, open ArcMap and add the lower-resolution colour image to the map using the "Add Data" button. Once the image is added, right-click on the raster layer in the table of contents and select "Properties".
The "Layer Properties" dialog box will appear. Click on the "Symbology" tab, then select "RGB Composite" from the "Show" menu. In the "Properties" list, scroll down to the bottom and check the box next to "Pan-sharpening".
Next, click on the "Panchromatic Image" drop-down arrow and select the higher-resolution image by clicking on the image name or using the browse button to locate it. Then, from the "Pan-sharpening Type" drop-down list, choose the desired colour transformation method.
You can also optionally fine-tune the process by typing weight values for the red, green, blue, and infrared bands. If your raster dataset includes an infrared band as the fourth band and you want to use it, make sure to check the "4th-band as Infrared Image" checkbox.
Additionally, it is recommended to set the display resampling to bilinear interpolation under the "Display" tab in the "Layer Properties" dialog box. This will help produce a less pixelated output image.
By following these steps and modifying the layer properties, you can effectively pan-sharpen your image in ArcGIS, enhancing the spatial resolution and improving the visualization of the multiband image.
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Image fusion methods
Image fusion is the process of combining two images, a multispectral image and a higher-resolution panchromatic image, to achieve higher spatial resolution in the multispectral image. There are five image fusion methods to choose from to create a pan-sharpened image in ArcGIS:
Brovey Transformation
The Brovey transformation uses red, green, and blue (RGB) and the panchromatic bands as inputs to output new red, green, and blue bands. The general equation is as follows:
Red_out = Red_in / [(blue_in + green_in + red_in) * Pan]
However, by using weights and the near-infrared band, the adjusted equation for each band becomes:
DNF = (P - IW * I) / (RW * R + GW * G + BW * B)
Red_out = R * DNF
Green_out = G * DNF
Blue_out = B * DNF
Infrared_out = I * DNF
Esri Pan Sharpening Transformation
The Esri pan-sharpening transformation uses a weighted average and the additional near-infrared band (optional) to create its pan-sharpened output bands. The result of the weighted average is used to create an adjustment value (ADJ) that is then used in calculating the output values:
ADJ = pan image - WA
Red_out = R + ADJ
Green_out = G + ADJ
Blue_out = B + ADJ
Near_Infrared_out = I + ADJ
Gram-Schmidt Spectral Sharpening Method
The Gram-Schmidt pan-sharpening method is based on a general algorithm for vector orthogonalization—the Gram-Schmidt orthogonalization. In this method, a low-resolution pan band is created by computing a weighted average of the MS bands. These bands are then decorrelated using the Gram-Schmidt orthogonalization algorithm, treating each band as one multidimensional vector. The low-resolution pan band is then replaced by the high-resolution pan band, and all bands are back-transformed in high resolution.
Intensity, Hue, Saturation (IHS) Transformation
The IHS transformation is a commonly used technique in image fusion that introduces important distortion on the pixel spectra, improving the information content of remote sensing images.
Simple Mean Transformation
This method uses a simple mean to improve the spatial resolution while maintaining the color of the image.
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Gram-Schmidt pan sharpening method
The Gram-Schmidt pan-sharpening method is one of the five image fusion methods offered by ArcGIS to create a pan-sharpened image. This method is based on a general algorithm for vector orthogonalization, called the Gram-Schmidt orthogonalization.
The Gram-Schmidt orthogonalization algorithm takes in vectors that are not orthogonal and rotates them so that they are orthogonal afterward. In the context of images, each band (panchromatic, red, green, blue, and infrared) corresponds to one high-dimensional vector, where the number of dimensions is equal to the number of pixels.
The first step in the Gram-Schmidt pan-sharpening method is to create a low-resolution pan band by computing a weighted average of the multispectral (MS) bands. These bands are then decorrelated using the Gram-Schmidt orthogonalization algorithm, treating each band as a multidimensional vector. The simulated low-resolution pan band is used as the first vector, which remains unrotated or untransformed.
Subsequently, the low-resolution pan band is replaced by the high-resolution pan band, and all bands are back-transformed in high resolution. This process enhances the spatial resolution while maintaining the color accuracy of the image.
Overall, the Gram-Schmidt pan-sharpening method in ArcGIS utilizes vector orthogonalization techniques to improve image sharpness and detail, making it a valuable tool for image analysis and enhancement.
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Saving the image
Once you have created the pan-sharpened image, you can save it by following these steps:
For the ArcGIS Desktop application, hold the CTRL key and click on a panchromatic raster layer in the Image Analysis window. The pan-sharpened image will appear as a temporary raster layer. To save this image, select it in the Image Analysis window and click the Export button.
For the ArcGIS .NET 10.8 SDK, the code to save the image is as follows:
Csharp
Public static void PanSharpening(IRasterDataset panDataset, IRasterDataset multiDataset)
{
//panDataset - A raster dataset created from a single-band, higher-resolution image
//multiDataset - A raster dataset created from a multiband image
IRaster panRaster = ((IRasterDataset2)panDataset).CreateFullRaster();
IRaster multiRaster = ((IRasterDataset2)multiDataset).CreateFullRaster();
IRasterBandCollection rasterbandCol = (IRasterBandCollection)multiRaster;
IRasterBandCollection infredRaster = new RasterClass();
InfredRaster.AppendBand(rasterbandCol.Item(3));
IRasterProps panSharpenRasterProps = (IRasterProps)multiRaster;
IRasterProps panRasterProps = (IRasterProps)panRaster;
PanSharpenRasterProps.Width = panRasterProps.Width;
PanSharpenRasterProps.Height = panRasterProps.Height;
PanSharpenRasterProps.Extent = panRasterProps.Extent;
MultiRaster.ResampleMethod = rstResamplingTypes.RSP_BilinearInterpolation;
IPansharpeningFilter pansharpenFilter = new PansharpeningFilterClass();
PansharpenFilter.InfraredImage = (IRaster)infredRaster;
PansharpenFilter.PanImage = (IRaster)panRaster;
PansharpenFilter.PansharpeningType = esriPansharpeningType.esriPansharpeningESRI;
PansharpenFilter.PutWeights(0.166, 0.167, 0.167, 0.5);
IPixelOperation pixelOperation = (IPixelOperation)multiRaster;
PixelOperation.PixelFilter = (IPixelFilter)pansharpenFilter;
ISaveAs saveas = (ISaveAs)pixelOperation;
Saveas.SaveAs(@"c:\temp\pansharpentest.tif", null, "TIFF");
}
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Frequently asked questions
Pan sharpening is the process of fusing a multispectral image with a higher-resolution panchromatic image to increase the spatial resolution of the multispectral image.
To pan sharpen an image in ArcGIS, you can use the Pan-sharpen button on the Image Analysis window. Alternatively, you can modify the layer properties by right-clicking the raster layer, opening the Properties, clicking the Symbology tab, selecting RGB Composite on the Show menu, checking Pan-sharpening, and selecting the desired colour transformation.
There are five image fusion methods to choose from when creating a pan-sharpened image: the Brovey transformation, the Esri pan-sharpening transformation, the Gram-Schmidt spectral sharpening method, the intensity, hue, saturation (IHS) transformation, and the simple mean transformation. Each method uses different models to improve spatial resolution while maintaining colour accuracy.
