The process of creating an indexed image may be better described as vector quantization VQ. VQ serves as a rounding process for multidimensional numbers. In this process, all the colors in your image get grouped based upon their similarity.

For a given group, all colors in that group are replaced by a single center point value, which minimizes error for colors in that cell or "site" if you're using the Voronoi terminology. In Figure 3, the green dots represent input colors, and the red dots are the center points that replace the input colors.

Each cell is bounded by blue lines. The result of applying VQ to an image reduces the number of unique colors, replacing each group of colors with a single color that's "pretty close" in visual quality. This technique also allows you to define the maximum number of unique colors in your image. For example, Figure 4 shows the a parrot head in Immediately, you can see that there's a loss of quality; most of the gradient colors have been replaced, imparting a banding effect to the image.

This image needs more than 16 unique colors. Setting up a VQ step in your pipeline can help you get a better sense of the true number of unique colors that your image uses, and can help you reduce them significantly. There are a number of readily available tools that you can use to help you implement this technique.

If you are using JPG images, there are several small changes you can make that potentially provide significant file-size savings. These include:. When choosing tools, remember that photo exporting tools can insert unnecessary metadata, such as GPS information, into your images.

At a minimum, try to leverage existing tools to help strip out this information from your files. WebP is a newer image format supported from Android 4. This format provides superior lossless and lossy compression for images on the web. Using WebP, developers can create smaller, richer images.

For more information about WebP, visit the WebP site. Different image formats are suitable for different types of images. Figure 5 shows two images that come out quite differently depending on which compression scheme the developer applies.

The image on the left has many small details, and thus compresses more efficiently with JPG. The image on the right, with runs of the same color, compresses more efficiently with PNG.

The only thing to keep in mind is that it only has native support on devices running Android 4. Fortunately, the large majority of devices satisfy that requirement. There are several techniques you can use to achieve the right balance between compression and image quality.

The other technique takes advantage of the Butteraugli library, and is usable for all image formats. The power of JPG and WebP comes from the fact that you can use a scalar value to balance quality against file size.

The trick is finding out what the correct quality value is for your image. Too low a quality level produces a small file at the cost of image quality. Too high a quality level increases file size without providing a noticeable benefit to the user.

The most straightforward solution is to pick some non-maximum value, and use that value. However, be aware that the quality value affects every image differently. You should make sure to test your chosen maximum value against a representative sample of images.

Also, make sure to perform all of your tests against the original images, and not on compressed versions. For large media applications that upload and re-send millions of JPGs a day, hand-tuning for each asset is impractical. You might address this challenge by specifying several different quality levels, according to image category. The Butteraugli project is a library to test an image's Psychovisual Error Threshold: the point at which a viewer starts to notice image degradation.

In other words, this project attempts to quantify how distorted your compressed image is. You can then choose the image that is the best balance of file size and Butteraugli level.

Butteraugli allows you to proceed based on either output or input. That is, you can look for the lowest quality setting before a user perceives noticeable distortion in the resulting image, or you can iteratively set image-distortion levels to learn their associated quality levels. It is tempting to keep only a single resolution of an image on a server. When a device accesses the image, the server serves it at that one resolution and leaves downscaling to the device. This solution is convenient for the developer, but potentially painful for the user, because the solution forces the user to download much more data than they need.

You should instead store multiple sizes of images, and serve the size that is most appropriate for a particular use case. For example, for a thumbnail, serving an actual thumbnail image instead of serving and downscaling a full-size version consumes much less network bandwidth.

This approach is good for download speed, and is less costly for users who may be using limited or metered data plans. Proceeding like this also results in the image's taking less space on the device and in main memory.

In the case of large images, such as 4K ones, this approach also saves the device from having to resize images before loading them. Implementing this approach requires that you have a backend image service to provide images at various resolutions with proper caching. There are existing services that can provide help with this task. For example, App Engine comes with image resizing functionality already installed.

Content and code samples on this page are subject to the licenses described in the Content License. App Basics. Build your first app. App resources. Resource types.

App manifest file. Device compatibility. Multiple APK support. Tablets, large screens, and foldables. Build responsive UIs. Build for foldables. Getting started. Creating the class includes extending the sync adapter base class, defining constructors for the class, and implementing the method where you define the data transfer tasks.

To create the sync adapter component, start by extending AbstractThreadedSyncAdapter and writing its constructors. Use the constructors to run setup tasks each time your sync adapter component is created from scratch, just as you use Activity. For example, if your app uses a content provider to store data, use the constructors to get a ContentResolver instance. Since a second form of the constructor was added in Android platform version 3.

Note: The sync adapter framework is designed to work with sync adapter components that are singleton instances. Instantiating the sync adapter component is covered in more detail in the section Bind the Sync Adapter to the Framework. The following example shows you how to implement AbstractThreadedSyncAdapter and its constructors:. The sync adapter component does not automatically do data transfer.

Instead, it encapsulates your data transfer code, so that the sync adapter framework can run the data transfer in the background, without involvement from your app. When the framework is ready to sync your application's data, it invokes your implementation of the method onPerformSync. To facilitate the transfer of data from your main app code to the sync adapter component, the sync adapter framework calls onPerformSync with the following arguments:.

The following snippet shows the overall structure of onPerformSync :. While the actual implementation of onPerformSync is specific to your app's data synchronization requirements and server connection protocols, there are a few general tasks your implementation should perform:.

Note: The sync adapter framework runs onPerformSync on a background thread, so you don't have to set up your own background processing. In addition to your sync-related tasks, you should try to combine your regular network-related tasks and add them to onPerformSync.

By concentrating all of your network tasks in this method, you conserve the battery power that's needed to start and stop the network interfaces. To learn more about making network access more efficient, see the training class Transferring Data Without Draining the Battery , which describes several network access tasks you can include in your data transfer code.

You now have your data transfer code encapsulated in a sync adapter component, but you have to provide the framework with access to your code. To do this, you need to create a bound Service that passes a special Android binder object from the sync adapter component to the framework. With this binder object, the framework can invoke the onPerformSync method and pass data to it. Instantiate your sync adapter component as a singleton in the onCreate method of the service.

By instantiating the component in onCreate , you defer creating it until the service starts, which happens when the framework first tries to run your data transfer. You need to instantiate the component in a thread-safe manner, in case the sync adapter framework queues up multiple executions of your sync adapter in response to triggers or scheduling.

For example, the following snippet shows you how to create a class that implements the bound Service , instantiates your sync adapter component, and gets the Android binder object:. Note: To see a more detailed example of a bound service for a sync adapter, see the sample app.

The sync adapter framework requires each sync adapter to have an account type. You declared the account type value in the section Add the Authenticator Metadata File. Now you have to set up this account type in the Android system. To set up the account type, add a placeholder account that uses the account type by calling addAccountExplicitly. The best place to call the method is in the onCreate method of your app's opening activity. The following code snippet shows you how to do this:.

To plug your sync adapter component into the framework, you need to provide the framework with metadata that describes the component and provides additional flags. The metadata specifies the account type you've created for your sync adapter, declares a content provider authority associated with your app, controls a part of the system user interface related to sync adapters, and declares other sync-related flags.

You can give any name to the file, although it's usually called syncadapter. The following example shows the XML for a sync adapter that uses a single placeholder account and only does downloads. Once you've added the sync adapter component to your app, you have to request permissions related to using the component, and you have to declare the bound Service you've added.

Since the sync adapter component runs code that transfers data between the network and the device, you need to request permission to access the Internet. In addition, your app needs to request permission to read and write sync adapter settings, so you can control the sync adapter programmatically from other components in your app.

You also need to request a special permission that allows your app to use the authenticator component you created in the lesson Creating a Stub Authenticator. SyncAdapter , sent by the system to run the sync adapter. When the filter is triggered, the system starts the bound service you've created, which in this example is SyncService.

If you have multiple sync adapters in your app they can share this process, which reduces overhead. The android:name attribute indicates that this metadata is for the sync adapter framework. The android:resource element specifies the name of the metadata file.

You now have all of the components for your sync adapter. The next lesson shows you how to tell the sync adapter framework to run your sync adapter, either in response to an event or on a regular schedule.

Content and code samples on this page are subject to the licenses described in the Content License. App Basics. Build your first app. App resources. Resource types. App manifest file. Device compatibility. Multiple APK support. Tablets, large screens, and foldables. Build responsive UIs. Build for foldables. This tutorial explains how to download Image using AsyncTask in Android.

The example below download image while showing progress bar while during download. AsyncTask enables proper and easy use of the UI thread. It allows performing background operations and passing the results on the UI thread. If you are doing something isolated related to UI, for example downloading data to present in a list, go ahead and use AsyncTask.

Since there is currently no comment field for examples or I haven't found it or I haven't permission for it here is some comment about this:. What is use in Android? AsyncTasks should ideally be used for short operations a few seconds at the most. As Google tells, for now, don't forget to add also readable on external storage in the manifest :. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How to download and save an image in Android Ask Question. Asked 8 years, 8 months ago. Active 2 months ago. Viewed k times. How do you download and save an image from a given url in Android? Lance Roberts Droidman Droidman Add a comment. Active Oldest Votes. Edit as of Just displaying an image using Picasso is as simple as: Picasso.

It uses its own ImageLoader that once initialized has a global instance which can be used to download images in a single line of code: ImageLoader. I have included examples for progressive JPEG's and animated images into the sample project. Conclusion - "I have learned about the great stuff, what should I use now?

If your app saves images or other files as a result of a user or an automated action and you don't need the images to be displayed often, use the Android DownloadManager. And here's the BasicImageDownloader. Bitmap; import android. BitmapFactory; import android. AsyncTask; import android. NonNull; import android. Log; import java. BufferedInputStream; import java. ByteArrayOutputStream; import java. File; import java.

FileOutputStream; import java. IOException; import java. InputStream; import java. URL; import java. URLConnection; import java. HashSet; import java. The URL is probably not pointing to a file".

What about the onPictureTaken callback which gives the picture as byte[], can one get a URL to that picture, straight from the camera? Or is basic old outputStream the only way in Android to save a picture which was taken by a camera without using the built in intent?

That seems strange, because the natural thing to do after onPictureTaken is of course to save it. Is there no particular support for doing that? Tombola Hi! This post is about downloading a picture from the web. But to answer your question as far as I've understood it : the common way of saving a camera picture is getting its path from the Cursor in the onActivityResult method , then creating a Bitmap using that path.

BartBurg this question is about downloading and saving an image.