Stretch renderer

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Use a stretch renderer to enhance the visual contrast of raster data for analysis.

Image of stretch renderer

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

  1. Create a Raster from a raster file.
  2. Create a RasterLayer from the Raster.
  3. Add the layer to the map.
  4. Create a StretchRenderer, specifying the stretch parameters and other properties.
  5. Apply the Renderer to 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:

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
                                                                                                                                                                                                                                                                                                                                                                     
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// 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");
        }

    }
}

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