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 ArcGISRuntime.Samples.Managers;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Rasters;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using System;
using System.Collections.Generic;
using UIKit;

namespace ArcGISRuntime.Samples.ChangeStretchRenderer
{
    [Register("ChangeStretchRenderer")]
    [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 : UIViewController
    {
        // Hold references to UI controls.
        private MapView _myMapView;
        private UISegmentedControl _rendererTypes;
        private UILabel _labelParameter1;
        private UITextField _inputParameter1;
        private UILabel _labelParameter2;
        private UITextField _inputParameter2;
        private UIButton _updateRendererButton;

        public ChangeStretchRenderer()
        {
            Title = "Stretch renderer";
        }

        private async void Initialize()
        {
            // Add an imagery basemap.
            _myMapView.Map = new Map(BasemapStyle.ArcGISImageryStandard);

            // Get the file name.
            string filepath = DataManager.GetDataFolder("95392f99970d4a71bd25951beb34a508", "shasta", "ShastaBW.tif");

            // Load the raster file.
            Raster rasterFile = new Raster(filepath);

            // Create the layer.
            RasterLayer rasterLayer = new RasterLayer(rasterFile);

            // Add the layer to the map.
            _myMapView.Map.OperationalLayers.Add(rasterLayer);

            try
            {
                // Wait for the layer to load.
                await rasterLayer.LoadAsync();

                // Set the viewpoint
                await _myMapView.SetViewpointGeometryAsync(rasterLayer.FullExtent);
            }
            catch (Exception e)
            {
                new UIAlertView("Error", e.ToString(), (IUIAlertViewDelegate)null, "OK", null).Show();
            }
        }

        private void rendererTypes_ValueChanged(object sender, EventArgs e)
        {
            // This function modifies the UI parameter controls depending on which stretch
            // renderer is chosen by the user.
            switch (_rendererTypes.SelectedSegment)
            {
                case 0: // Min Max.
                    // Make sure all the GUI items are visible.
                    _labelParameter1.Hidden = false;
                    _labelParameter2.Hidden = false;
                    _inputParameter1.Hidden = false;
                    _inputParameter2.Hidden = false;

                    // Define what values/options the user sees.
                    _labelParameter1.Text = "Minimum value (0 - 255):";
                    _labelParameter2.Text = "Maximum value (0 - 255):";
                    _inputParameter1.Text = "10";
                    _inputParameter2.Text = "150";

                    break;

                case 1: // Percent Clip.
                    // Make sure all the GUI items are visible.
                    _labelParameter1.Hidden = false;
                    _labelParameter2.Hidden = false;
                    _inputParameter1.Hidden = false;
                    _inputParameter2.Hidden = false;

                    // Define what values/options the user sees.
                    _labelParameter1.Text = "Minimum (0 - 100):";
                    _labelParameter2.Text = "Maximum (0 - 100):";
                    _inputParameter1.Text = "0";
                    _inputParameter2.Text = "50";

                    break;

                case 2: // Standard Deviation.
                    // Make sure that only the necessary GUI items are visible.
                    _labelParameter1.Hidden = false;
                    _labelParameter2.Hidden = true;
                    _inputParameter1.Hidden = false;
                    _inputParameter2.Hidden = true;

                    // Define what values/options the user sees.
                    _labelParameter1.Text = "Factor (.25 to 4):";
                    _inputParameter1.Text = "0.5";

                    break;
            }
        }

        private void UpdateRendererButton_Clicked(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(_inputParameter1.Text);
                input2 = Convert.ToDouble(_inputParameter2.Text);
            }
            catch (Exception ex)
            {
                new UIAlertView("alert", ex.Message, (IUIAlertViewDelegate)null, "OK", null).Show();
                return;
            }

            // Create an IEnumerable from an empty list of doubles for the gamma values in the stretch render.
            IEnumerable<double> gammaValues = new List<double>();

            // Create a color ramp for the stretch renderer.
            ColorRamp colorRamp = ColorRamp.Create(PresetColorRampType.DemLight, 1000);

            // Create the place holder for the stretch renderer.
            StretchRenderer stretchRenderer = null;

            switch (_rendererTypes.SelectedSegment)
            {
                case 0:

                    // 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.

                    try
                    {
                        // Create an IEnumerable from a list of double min stretch value doubles.
                        IEnumerable<double> minValues = new List<double> { input1 };

                        // Create an IEnumerable from a list of double max stretch value doubles.
                        IEnumerable<double> maxValues = new List<double> { input2 };

                        // Create a new MinMaxStretchParameters based on the user choice for min and max stretch values.
                        MinMaxStretchParameters minMaxStretchParameters = new MinMaxStretchParameters(minValues, maxValues);

                        // Create the stretch renderer based on the user defined min/max stretch values, empty gamma values, statistic estimates, and a predefined color ramp.
                        stretchRenderer = new StretchRenderer(minMaxStretchParameters, gammaValues, true, colorRamp);
                    }
                    catch (ArgumentException)
                    {
                        ShowMessage("Error configuring renderer.", "Ensure all values are valid and try again.");
                        return;
                    }

                    break;

                case 1:

                    // 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.

                    try
                    {
                        // Create a new PercentClipStretchParameters based on the user choice for min and max percent clip values.
                        PercentClipStretchParameters percentClipStretchParameters = 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.
                        stretchRenderer = new StretchRenderer(percentClipStretchParameters, gammaValues, true, colorRamp);
                    }
                    catch (Exception)
                    {
                        ShowMessage("Error configuring renderer.", "Ensure all values are valid and try again.");
                        return;
                    }

                    break;

                case 2:

                    // 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

                    try
                    {
                        // Create a new StandardDeviationStretchParameters based on the user choice for standard deviation value.
                        StandardDeviationStretchParameters standardDeviationStretchParameters = 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.
                        stretchRenderer = new StretchRenderer(standardDeviationStretchParameters, gammaValues, true, colorRamp);
                    }
                    catch (Exception)
                    {
                        ShowMessage("Error configuring renderer.", "Ensure all values are valid and try again.");
                        return;
                    }

                    break;
            }

            // Get the existing raster layer in the map.
            RasterLayer rasterLayer = (RasterLayer)_myMapView.Map.OperationalLayers[0];

            // Apply the stretch renderer to the raster layer.
            rasterLayer.Renderer = stretchRenderer;
        }

        private void ShowMessage(string title, string message)
        {
            new UIAlertView(title, message, (IUIAlertViewDelegate)null, "OK", null).Show();
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            Initialize();
        }

        public override void LoadView()
        {
            // Create the views.
            View = new UIView { BackgroundColor = ApplicationTheme.BackgroundColor };

            UIView formContainer = new UIView();
            formContainer.TranslatesAutoresizingMaskIntoConstraints = false;
            formContainer.BackgroundColor = ApplicationTheme.BackgroundColor;

            _myMapView = new MapView();
            _myMapView.TranslatesAutoresizingMaskIntoConstraints = false;

            _inputParameter1 = new UITextField();
            _inputParameter1.TranslatesAutoresizingMaskIntoConstraints = false;
            _inputParameter1.BorderStyle = UITextBorderStyle.RoundedRect;

            _inputParameter2 = new UITextField();
            _inputParameter2.TranslatesAutoresizingMaskIntoConstraints = false;
            _inputParameter2.BorderStyle = UITextBorderStyle.RoundedRect;

            _labelParameter1 = new UILabel();
            _labelParameter1.TextAlignment = UITextAlignment.Right;
            _labelParameter1.TranslatesAutoresizingMaskIntoConstraints = false;

            _labelParameter2 = new UILabel();
            _labelParameter2.TextAlignment = UITextAlignment.Right;
            _labelParameter2.TranslatesAutoresizingMaskIntoConstraints = false;

            _updateRendererButton = new UIButton();
            _updateRendererButton.SetTitle("Update renderer", UIControlState.Normal);
            _updateRendererButton.SetTitleColor(View.TintColor, UIControlState.Normal);
            _updateRendererButton.TranslatesAutoresizingMaskIntoConstraints = false;

            _rendererTypes = new UISegmentedControl("Min/Max", "% Clip", "Std. Deviation");
            _rendererTypes.SelectedSegment = 0;
            _rendererTypes.TintColor = View.TintColor;
            _rendererTypes.TranslatesAutoresizingMaskIntoConstraints = false;

            // Call a function to configure the labels appropriately
            rendererTypes_ValueChanged(_rendererTypes, null);

            // Add the views.
            View.AddSubviews(_myMapView, formContainer, _rendererTypes, _inputParameter1,
                _inputParameter2, _labelParameter1, _labelParameter2, _updateRendererButton);

            // Lay out the views.
            NSLayoutConstraint.ActivateConstraints(new[]
            {
                _rendererTypes.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor, 8),
                _rendererTypes.LeadingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.LeadingAnchor, 8),
                _rendererTypes.TrailingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TrailingAnchor, -8),

                _inputParameter1.TopAnchor.ConstraintEqualTo(_rendererTypes.BottomAnchor, 8),
                _inputParameter1.TrailingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TrailingAnchor, -8),
                _inputParameter1.WidthAnchor.ConstraintEqualTo(72),

                _inputParameter2.TopAnchor.ConstraintEqualTo(_inputParameter1.BottomAnchor, 8),
                _inputParameter2.TrailingAnchor.ConstraintEqualTo(_inputParameter1.TrailingAnchor),
                _inputParameter2.WidthAnchor.ConstraintEqualTo(_inputParameter1.WidthAnchor),

                _updateRendererButton.TopAnchor.ConstraintEqualTo(_inputParameter2.BottomAnchor, 8),
                _updateRendererButton.LeadingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.LeadingAnchor),
                _updateRendererButton.TrailingAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TrailingAnchor),

                _labelParameter1.TopAnchor.ConstraintEqualTo(_inputParameter1.TopAnchor),
                _labelParameter1.LeadingAnchor.ConstraintEqualTo(_rendererTypes.LeadingAnchor),
                _labelParameter1.TrailingAnchor.ConstraintEqualTo(_inputParameter1.LeadingAnchor, -8),
                _labelParameter1.BottomAnchor.ConstraintEqualTo(_inputParameter1.BottomAnchor),

                _labelParameter2.TopAnchor.ConstraintEqualTo(_inputParameter2.TopAnchor),
                _labelParameter2.BottomAnchor.ConstraintEqualTo(_inputParameter2.BottomAnchor),
                _labelParameter2.LeadingAnchor.ConstraintEqualTo(_labelParameter1.LeadingAnchor),
                _labelParameter2.TrailingAnchor.ConstraintEqualTo(_labelParameter1.TrailingAnchor),

                formContainer.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                formContainer.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                formContainer.BottomAnchor.ConstraintEqualTo(_updateRendererButton.BottomAnchor, 8),
                formContainer.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),

                _myMapView.TopAnchor.ConstraintEqualTo(formContainer.BottomAnchor),
                _myMapView.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _myMapView.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                _myMapView.BottomAnchor.ConstraintEqualTo(View.BottomAnchor)
            });
        }

        private bool HandleTextField(UITextField textField)
        {
            // This method allows pressing 'return' to dismiss the software keyboard.
            textField.ResignFirstResponder();
            return true;
        }

        public override void ViewWillAppear(bool animated)
        {
            base.ViewWillAppear(animated);

            // Subscribe to events.
            _inputParameter1.ShouldReturn += HandleTextField;
            _inputParameter2.ShouldReturn += HandleTextField;
            _updateRendererButton.TouchUpInside += UpdateRendererButton_Clicked;
            _rendererTypes.ValueChanged += rendererTypes_ValueChanged;
        }

        public override void ViewDidDisappear(bool animated)
        {
            base.ViewDidDisappear(animated);

            // Unsubscribe from events, per best practice.
            _inputParameter1.ShouldReturn -= HandleTextField;
            _inputParameter2.ShouldReturn -= HandleTextField;
            _updateRendererButton.TouchUpInside -= UpdateRendererButton_Clicked;
            _rendererTypes.ValueChanged -= rendererTypes_ValueChanged;
        }
    }
}

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