Android how to create runtime thumbnail

Question

I have a large sized image. At runtime, I want to read the image from storage and scale it so that its weight and size gets reduced and I can use it as a thumbnail. When a u

Answer 1

Use BitmapFactory.decodeFile(...) to get your Bitmap object and set it to an ImageView with ImageView.setImageBitmap().

On the ImageView set the layout dimensions to something small, eg:

android:layout_width="66dip" android:layout_height="48dip"

Add an onClickListener to the ImageView and launch a new activity, where you display the image in full size with

android:layout_width="wrap_content" android:layout_height="wrap_content"

or specify some larger size.

Answer 2

The best solution I found is the following. Compared with the other solutions this one does not need to load the full image for creating a thumbnail, so it is more efficient! Its limit is that you can not have a thumbnail with exact width and height but the solution as near as possible.

File file = ...; // the image file

Options bitmapOptions = new Options();
bitmapOptions.inJustDecodeBounds = true; // obtain the size of the image, without loading it in memory
BitmapFactory.decodeFile(file.getAbsolutePath(), bitmapOptions);

// find the best scaling factor for the desired dimensions
int desiredWidth = 400;
int desiredHeight = 300;
float widthScale = (float)bitmapOptions.outWidth/desiredWidth;
float heightScale = (float)bitmapOptions.outHeight/desiredHeight;
float scale = Math.min(widthScale, heightScale);

int sampleSize = 1;
while (sampleSize < scale) {
    sampleSize *= 2;
}
bitmapOptions.inSampleSize = sampleSize; // this value must be a power of 2,
                                         // this is why you can not have an image scaled as you would like
bitmapOptions.inJustDecodeBounds = false; // now we want to load the image

// Let's load just the part of the image necessary for creating the thumbnail, not the whole image
Bitmap thumbnail = BitmapFactory.decodeFile(file.getAbsolutePath(), bitmapOptions);

// Save the thumbnail
File thumbnailFile = ...;
FileOutputStream fos = new FileOutputStream(thumbnailFile);
thumbnail.compress(Bitmap.CompressFormat.JPEG, 90, fos);
fos.flush();
fos.close();

// Use the thumbail on an ImageView or recycle it!
thumbnail.recycle();

Answer 3

Try this

Bitmap ThumbImage = ThumbnailUtils.extractThumbnail(BitmapFactory.decodeFile(imagePath), THUMBSIZE, THUMBSIZE);

This Utility is available from API_LEVEl 8. [Source]

Answer 4

My Solution

byte[] imageData = null;

        try     
        {

            final int THUMBNAIL_SIZE = 64;

            FileInputStream fis = new FileInputStream(fileName);
            Bitmap imageBitmap = BitmapFactory.decodeStream(fis);

            imageBitmap = Bitmap.createScaledBitmap(imageBitmap, THUMBNAIL_SIZE, THUMBNAIL_SIZE, false);

            ByteArrayOutputStream baos = new ByteArrayOutputStream();  
            imageBitmap.compress(Bitmap.CompressFormat.JPEG, 100, baos);
            imageData = baos.toByteArray();

        }
        catch(Exception ex) {

        }

Answer 5

I found an easy way to do this

Bitmap thumbnail = ThumbnailUtils.extractThumbnail(BitmapFactory.decodeFile(mPath),200,200)

Syntax

Bitmap thumbnail = ThumbnailUtils.extractThumbnail(Bitmap source,int width,int height)

OR

use Picasso dependancy

compile 'com.squareup.picasso:picasso:2.5.2'

Picasso.with(context)
    .load("file:///android_asset/DvpvklR.png")
    .resize(50, 50)
    .into(imageView2);

Reference Picasso

Answer 6

/**
 * Creates a centered bitmap of the desired size.
 *
 * @param source original bitmap source
 * @param width targeted width
 * @param height targeted height
 * @param options options used during thumbnail extraction
 */
public static Bitmap extractThumbnail(
        Bitmap source, int width, int height, int options) {
    if (source == null) {
        return null;
    }

    float scale;
    if (source.getWidth() < source.getHeight()) {
        scale = width / (float) source.getWidth();
    } else {
        scale = height / (float) source.getHeight();
    }
    Matrix matrix = new Matrix();
    matrix.setScale(scale, scale);
    Bitmap thumbnail = transform(matrix, source, width, height,
            OPTIONS_SCALE_UP | options);
    return thumbnail;
}