Subsampling Zoom Image View

This library includes two classes, ScaleImageView and SubsamplingScaleImageView. SubsamplingScaleImageView is best for large images but doesn't support display of Bitmap objects or resources, and ScaleImageView supports Bitmap objects but not subsampling or large images. To decide which is best for you, see below.

Download the sample app

Custom image views for Android with pinch to zoom, panning, rotation and animation support, with easy extension so you can add your own overlays and touch event detection.

SubsamplingScaleImageView uses subsampling and tiles to support large images. While zooming in, the low resolution, full size base layer is overlaid with smaller tiles at least as high resolution as the screen, and tiles are loaded and discarded during panning to avoid holding too much bitmap data in memory. This is ideal for use in image gallery apps where the size of the images may be large enough to require subsampling, and where pinch to zoom is required to view the high resolution detail.

These views don't extend ImageView and aren't intended as a general purpose replacement for it. They're specialised for the display of photos and other large images, not the display of 9-patches, shapes and the other types of drawable that ImageView supports.

Image display

• Display images from assets or the file system
• Automatically rotate images from the file system (e.g. the camera or gallery) according to EXIF
• Manually rotate images in 90° increments
• Swap images at runtime

SubsamplingScaleImageView only:

• Display huge images, larger than can be loaded into memory
• Show high resolution detail on zooming in
• Tested up to 20,000x13,000px, though larger images are slower

Gesture detection

• One finger pan
• Two finger pinch to zoom
• Pan while zooming
• Seamless switch between pan and zoom
• Fling momentum after panning
• Double tap to zoom in and out
• Options to disable pan and/or zoom gestures

Animation

• Public methods for animating the scale and center
• Customisable duration and easing
• Optional uninterruptible animations

Overridable event detection

• Supports OnClickListener and OnLongClickListener
• Supports interception of events using GestureDetector and OnTouchListener
• Extend to add your own gestures

Easy integration

• Use within a ViewPager to create a photo gallery
• Easily restore scale, center and orientation after screen rotation
• Can be extended to add overlay graphics that move and scale with the image
• Handles view resizing and wrap_content layout

Limitations

• SubsamplingScaleImageView requires SDK 10 (Gingerbread).
• SubsamplingScaleImageView cannot decode an image from resources or display a Bitmap object - the image file needs to be in assets or external storage.
• These views do not extend ImageView so attributes including android:tint, android:scaleType and android:src are not supported.
• Images stored in assets cannot be rotated based on EXIF, you'll need to do it manually. You probably know the orientation of your own assets :-)

Which view is best?

Use SubsamplingScaleImageView if:

• You want to zoom into very large images without losing detail.
• You need to display images of unknown size e.g. from the camera or gallery.
• You don't know if the images may be too large to fit in memory on some devices.
• You need to display images larger than 2048px.
• You don't need to support devices older than SDK 10.

Use ScaleImageView if:

• You know the size of the images you're displaying.
• You know the images are small enough to fit in memory on all your target devices.
• Your images are no larger than 2048px, or you are able to scale them down.
• You need to support devices older than SDK 10.

Quality notes

Images are decoded as dithered RGB_565 bitmaps by default, because this requires half as much memory as ARGB_8888. For most JPGs you won't notice the difference in quality. If you are displaying large PNGs with alpha channels, Android will probably decode them as ARGB_8888, and this may cause OutOfMemoryErrors. If possible, remove the alpha channel from PNGs larger than about 2,000x2,000. This allows them to be decoded as RGB_565.

Basic setup

Checkout the project and import the library project as a module in your app. Alternatively you can just copy the classes in com.davemorrissey.labs.subscaleview to your project.

Add the view to your layout XML as shown below. Normally you should set width and height to match_parent.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>

Now, in your fragment or activity, set the image asset name or file path.

SubsamplingScaleImageView imageView = (SubsamplingScaleImageView)findViewById(id.imageView);
imageView.setImageAsset("map.png");
// ... or ...
imageView.setImageFile("/sdcard/DCIM/DSCM00123.JPG");

That's it! Keep reading for some more options.

Define asset name in XML

For a zero code approach to showing an image from your assets, you need to define the custom namespace in your layout.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:ssiv="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
        ssiv:assetName="map.png"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
        
</RelativeLayout>

This method doesn't support restoring state after a screen orientation change.

Handle screen orientation changes

If you want the current scale, center and orientation to be preserved when the screen is rotated, you can request it from the view's getState method, and restore it after rotation, by passing it to the view along with the image asset name or file path. Here's a simple example of how you might do this in a fragment.

private static final String BUNDLE_STATE = "ImageViewState";

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.my_fragment, container, false);
    
    ImageViewState imageViewState = null;
    if (savedInstanceState != null && savedInstanceState.containsKey(BUNDLE_STATE)) {
        imageViewState = (ImageViewState)savedInstanceState.getSerializable(BUNDLE_STATE);
    }
    SubsamplingScaleImageView imageView = (SubsamplingScaleImageView)rootView.findViewById(id.imageView);
    imageView.setImageAsset("map.png", imageViewState);
    
    return rootView;
}

@Override
public void onSaveInstanceState(Bundle outState) {
    View rootView = getView();
    if (rootView != null) {
        SubsamplingScaleImageView imageView = (SubsamplingScaleImageView)rootView.findViewById(id.imageView);
        ImageViewState state = imageView.getState();
        if (state != null) {
            outState.putSerializable(BUNDLE_STATE, imageView.getState());
        }
    }
}

Extending functionality

Take a look at the sample app for examples of classes that overlay graphics on top of the image so that they move and scale with it. FreehandView adds event detection, capturing only the touch events it needs so pan and zoom still work normally.

About

Copyright 2014 David Morrissey, and licensed under the Apache License, Version 2.0. No attribution is necessary but it's very much appreciated. Star this project to show your gratitude.

This project started life as a way of showing very large images (e.g. a large building floor plan) with gestures to pan and zoom, with support for extensions that showed overlays (location pins, annotations) aligned with the image. It's grown massively, but for the moment I am keeping everything in one class to prevent subclasses and extensions breaking the assumptions (or violating invariants) on which the class depends.