Use a stretch renderer to enhance the visual contrast of raster data for analysis.
Use case
An appropriate stretch renderer can enhance the contrast of raster imagery, allowing the user to control how their data is displayed for efficient imagery analysis.
How to use the sample
Choose one of the stretch parameter types:
- Standard deviation - a linear stretch defined by the standard deviation of the pixel values
- Min-max - a linear stretch based on minimum and maximum pixel values
- Percent clip - a linear stretch between the defined percent clip minimum and percent clip maximum pixel values
Then configure the parameters and tap 'Update renderer'.
How it works
- Create a
Rasterfrom a raster file. - Create a
RasterLayerfrom theRaster. - Add the layer to the map.
- Create a
StretchRenderer, specifying the stretch parameters and other properties. - Apply the
Rendererto the raster layer.
Relevant API
- ColorRamp
- MinMaxStretchParameters
- PercentClipStretchParameters
- Raster
- RasterLayer
- StandardDeviationStretchParameters
- StretchParameters
- StretchRenderer
Offline data
This sample downloads the following items from ArcGIS Online automatically:
- raster-file.zip - Tif raster file
About the data
This sample uses a raster imagery tile of an area of forested mountainous terrain and rivers.
Additional information
See Stretch function in the ArcMap documentation for more information about the types of stretches that can be performed.
Tags
analysis, deviation, histogram, imagery, interpretation, min-max, percent clip, pixel, raster, stretch, symbology, visualization
Sample Code
ChangeStretchRenderer.cs
// Copyright 2018 Esri.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
// You may obtain a copy of the License at: http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific
// language governing permissions and limitations under the License.
using Android.App;
using Android.OS;
using Android.Widget;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Rasters;
using Esri.ArcGISRuntime.UI.Controls;
using System;
using System.Collections.Generic;
using ArcGISRuntime.Samples.Managers;
namespace ArcGISRuntime.Samples.ChangeStretchRenderer
{
[Activity (ConfigurationChanges=Android.Content.PM.ConfigChanges.Orientation | Android.Content.PM.ConfigChanges.ScreenSize)]
[ArcGISRuntime.Samples.Shared.Attributes.OfflineData("95392f99970d4a71bd25951beb34a508")]
[ArcGISRuntime.Samples.Shared.Attributes.Sample(
name: "Stretch renderer",
category: "Layers",
description: "Use a stretch renderer to enhance the visual contrast of raster data for analysis.",
instructions: "Choose one of the stretch parameter types:",
tags: new[] { "analysis", "deviation", "histogram", "imagery", "interpretation", "min-max", "percent clip", "pixel", "raster", "stretch", "symbology", "visualization" })]
public class ChangeStretchRenderer : Activity
{
// Global reference to the MapView used in the sample
private MapView _myMapView;
// Global reference to a list view of stretch render choices the user can choose from
private ListView _RendererTypes;
// Global reference to a label that displays the 1st parameter used by the stretch renderer
private TextView _Label_Parameter1;
// Global reference to the 1st parameter used by the stretch renderer that the user can modify
private EditText _Input_Parameter1;
// Global reference to a label that displays the 2nd parameter used by the stretch renderer
private TextView _Label_Parameter2;
// Global reference to the 2nd parameter used by the stretch renderer that the user can modify
private EditText _Input_Parameter2;
// Global reference to button the user clicks to change the stretch renderer on the raster
private Button _UpdateRenderer;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
Title = "Stretch renderer";
// Create the layout
CreateLayout();
// Initialize the app
Initialize();
}
private void CreateLayout()
{
// This section creates the UI elements and adds them to the layout view of the GUI
// Create a stack layout
LinearLayout layout = new LinearLayout(this) { Orientation = Orientation.Vertical };
// Create a list of stretch renderer choices the user can choose from
_RendererTypes = new ListView(this);
_RendererTypes.ItemClick += RendererTypes_SelectionChanged;
layout.AddView(_RendererTypes);
// ------------
// Create a sub layout to organize the label and 1st parameter on a single horizontal line
LinearLayout subLayout1 = new LinearLayout(this) { Orientation = Orientation.Horizontal };
// Create label that displays the 1st parameter used by the stretch renderer
_Label_Parameter1 = new TextView(this)
{
Text = "Minimum value (0 - 255):"
};
subLayout1.AddView(_Label_Parameter1);
// Create text field for 1st parameter used by the stretch renderer that the user can modify
_Input_Parameter1 = new EditText(this)
{
Text = "10"
};
subLayout1.AddView(_Input_Parameter1);
// Add the sub layout to the main layout
layout.AddView(subLayout1);
// ------------
// Create a sub layout to organize the label and 2nd parameter on a single horizontal line
LinearLayout subLayout2 = new LinearLayout(this) { Orientation = Orientation.Horizontal };
// Create label that displays the 2nd parameter used by the stretch renderer
_Label_Parameter2 = new TextView(this)
{
Text = "Maximum value (0 - 255):"
};
subLayout2.AddView(_Label_Parameter2);
// Create text field for 2nd parameter used by the stretch renderer that the user can modify
_Input_Parameter2 = new EditText(this)
{
Text = "150"
};
subLayout2.AddView(_Input_Parameter2);
// Add the sub layout to the main layout
layout.AddView(subLayout2);
// ------------
// Create button to change stretch renderer of the raster
_UpdateRenderer = new Button(this)
{
Text = "Update Renderer"
};
// Hook to touch/click event of the button
_UpdateRenderer.Click += OnUpdateRendererClicked;
layout.AddView(_UpdateRenderer);
// Create the map view and add it to the main layout
_myMapView = new MapView(this);
layout.AddView(_myMapView);
// Set the layout as the sample view
SetContentView(layout);
}
private async void Initialize()
{
// Create a simple string array of the human-readable stretch renderer names from the ObservableCollection
string[] myStringArray_RendererTypes = { "Min Max", "Percent Clip", "Standard Deviation" };
// Create an ArrayAdapter from the simple string array
ArrayAdapter myArrayAdapter_LayerNamesInTheMap = new ArrayAdapter<string>(this, Android.Resource.Layout.SimpleListItem1, myStringArray_RendererTypes);
// Display the human-readable stretch renderer names to be displayed a ListView
_RendererTypes.Adapter = myArrayAdapter_LayerNamesInTheMap;
// Add an imagery basemap
_myMapView.Map = new Map(BasemapStyle.ArcGISImageryStandard);
// Get the file name
string filepath = GetRasterPath();
// Load the raster file
Raster myRasterFile = new Raster(filepath);
// Create the layer
RasterLayer myRasterLayer = new RasterLayer(myRasterFile);
// Add the layer to the map
_myMapView.Map.OperationalLayers.Add(myRasterLayer);
try
{
// Wait for the layer to load
await myRasterLayer.LoadAsync();
// Set the viewpoint
await _myMapView.SetViewpointGeometryAsync(myRasterLayer.FullExtent);
}
catch (Exception e)
{
new AlertDialog.Builder(this).SetMessage(e.ToString()).SetTitle("Error").Show();
}
}
private void OnUpdateRendererClicked(object sender, EventArgs e)
{
// This function acquires the user selection of the stretch renderer from the table view
// along with the parameters specified, then a stretch renderer is created and applied to
// the raster layer
// Convert the input text to doubles and return if they're invalid.
double input1;
double input2;
try
{
input1 = Convert.ToDouble(_Input_Parameter1.Text);
input2 = Convert.ToDouble(_Input_Parameter2.Text);
}
catch (Exception ex)
{
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.SetMessage(ex.Message).SetTitle("Alert").Show();
return;
}
// Get the user choice for the raster stretch render
string myRendererTypeChoice;
if (_RendererTypes.SelectedItem == null)
{
// If the user does not click on a choice in the table but just clicks the
// button, the selected value will be null so use the initial
// stretch renderer option
myRendererTypeChoice = "Min Max";
}
else
{
// The user clicked on an option in the table and thus the selected value
// will contain a valid choice
myRendererTypeChoice = _RendererTypes.SelectedItem.ToString();
}
// Create an IEnumerable from an empty list of doubles for the gamma values in the stretch render
IEnumerable<double> myGammaValues = new List<double>();
// Create a color ramp for the stretch renderer
ColorRamp myColorRamp = ColorRamp.Create(PresetColorRampType.DemLight, 1000);
// Create the place holder for the stretch renderer
StretchRenderer myStretchRenderer = null;
switch (myRendererTypeChoice)
{
case "Min Max":
// This section creates a stretch renderer based on a MinMaxStretchParameters
// TODO: Add you own logic to ensure that accurate min/max stretch values are used
// Create an IEnumerable from a list of double min stretch value doubles
IEnumerable<double> myMinValues = new List<double> { input1 };
// Create an IEnumerable from a list of double max stretch value doubles
IEnumerable<double> myMaxValues = new List<double> { input2 };
// Create a new MinMaxStretchParameters based on the user choice for min and max stretch values
MinMaxStretchParameters myMinMaxStretchParameters = new MinMaxStretchParameters(myMinValues, myMaxValues);
// Create the stretch renderer based on the user defined min/max stretch values, empty gamma values, statistic estimates, and a predefined color ramp
myStretchRenderer = new StretchRenderer(myMinMaxStretchParameters, myGammaValues, true, myColorRamp);
break;
case "Percent Clip":
// This section creates a stretch renderer based on a PercentClipStretchParameters
// TODO: Add you own logic to ensure that accurate min/max percent clip values are used
// Create a new PercentClipStretchParameters based on the user choice for min and max percent clip values
PercentClipStretchParameters myPercentClipStretchParameters = new PercentClipStretchParameters(input1, input2);
// Create the percent clip renderer based on the user defined min/max percent clip values, empty gamma values, statistic estimates, and a predefined color ramp
myStretchRenderer = new StretchRenderer(myPercentClipStretchParameters, myGammaValues, true, myColorRamp);
break;
case "Standard Deviation":
// This section creates a stretch renderer based on a StandardDeviationStretchParameters
// TODO: Add you own logic to ensure that an accurate standard deviation value is used
// Create a new StandardDeviationStretchParameters based on the user choice for standard deviation value
StandardDeviationStretchParameters myStandardDeviationStretchParameters = new StandardDeviationStretchParameters(input1);
// Create the standard deviation renderer based on the user defined standard deviation value, empty gamma values, statistic estimates, and a predefined color ramp
myStretchRenderer = new StretchRenderer(myStandardDeviationStretchParameters, myGammaValues, true, myColorRamp);
break;
}
// Get the existing raster layer in the map
RasterLayer myRasterLayer = (RasterLayer)_myMapView.Map.OperationalLayers[0];
// Apply the stretch renderer to the raster layer
myRasterLayer.Renderer = myStretchRenderer;
}
private void RendererTypes_SelectionChanged(object sender, AdapterView.ItemClickEventArgs e)
{
// This function modifies the UI parameter controls depending on which stretch
// renderer is chosen by the user when clicking the table view
// Get the TextView from the AdapterView.ItemClickEventArgs
TextView myTextView = (TextView)e.View;
// Get the user choice for the raster stretch render from the TextView
string myRendererTypeChoice = myTextView.Text;
switch (myRendererTypeChoice)
{
case "Min Max":
// This section displays/resets the user choice options for MinMaxStretchParameters
// Make sure all the GUI items are visible
_Label_Parameter1.Visibility = Android.Views.ViewStates.Visible;
_Label_Parameter2.Visibility = Android.Views.ViewStates.Visible;
_Input_Parameter1.Visibility = Android.Views.ViewStates.Visible;
_Input_Parameter2.Visibility = Android.Views.ViewStates.Visible;
// Define what values/options the user sees
_Label_Parameter1.Text = "Minimum value (0 - 255):";
_Label_Parameter2.Text = "Maximum value (0 - 255):";
_Input_Parameter1.Text = "10";
_Input_Parameter2.Text = "150";
break;
case "Percent Clip":
// This section displays/resets the user choice options for PercentClipStretchParameters
// Make sure all the GUI items are visible
_Label_Parameter1.Visibility = Android.Views.ViewStates.Visible;
_Label_Parameter2.Visibility = Android.Views.ViewStates.Visible;
_Input_Parameter1.Visibility = Android.Views.ViewStates.Visible;
_Input_Parameter2.Visibility = Android.Views.ViewStates.Visible;
// Define what values/options the user sees
_Label_Parameter1.Text = "Minimum (0 - 100):";
_Label_Parameter2.Text = "Maximum (0 - 100)";
_Input_Parameter1.Text = "0";
_Input_Parameter2.Text = "50";
break;
case "Standard Deviation":
// This section displays/resets the user choice options for StandardDeviationStretchParameters
// Make sure that only the necessary GUI items are visible
_Label_Parameter1.Visibility = Android.Views.ViewStates.Visible;
_Label_Parameter2.Visibility = Android.Views.ViewStates.Invisible;
_Input_Parameter1.Visibility = Android.Views.ViewStates.Visible;
_Input_Parameter2.Visibility = Android.Views.ViewStates.Invisible;
// Define what values/options the user sees
_Label_Parameter1.Text = "Factor (.25 to 4):";
_Input_Parameter1.Text = "0.5";
break;
}
}
private static string GetRasterPath()
{
return DataManager.GetDataFolder("95392f99970d4a71bd25951beb34a508", "shasta", "ShastaBW.tif");
}
}
}