Java tutorial
//package com.java2s; import android.graphics.Bitmap; import android.graphics.Canvas; import android.graphics.Matrix; import android.graphics.Rect; public class Main { private static final int OPTIONS_SCALE_UP = 0x1; /** * Constant used to indicate we should recycle the input in * {@link #extractThumbnail(Bitmap, int, int, int)} unless the output is the * input. */ public static final int OPTIONS_RECYCLE_INPUT = 0x2; /** * Transform source Bitmap to targeted width and height. */ private static Bitmap transform(Matrix scaler, Bitmap source, int targetWidth, int targetHeight, int options) { boolean scaleUp = (options & OPTIONS_SCALE_UP) != 0; boolean recycle = (options & OPTIONS_RECYCLE_INPUT) != 0; int deltaX = source.getWidth() - targetWidth; int deltaY = source.getHeight() - targetHeight; if (!scaleUp && (deltaX < 0 || deltaY < 0)) { /* * In this case the bitmap is smaller, at least in one dimension, * than the target. Transform it by placing as much of the image as * possible into the target and leaving the top/bottom or left/right * (or both) black. */ Bitmap b2 = Bitmap.createBitmap(targetWidth, targetHeight, Bitmap.Config.ARGB_8888); Canvas c = new Canvas(b2); int deltaXHalf = Math.max(0, deltaX / 2); int deltaYHalf = Math.max(0, deltaY / 2); Rect src = new Rect(deltaXHalf, deltaYHalf, deltaXHalf + Math.min(targetWidth, source.getWidth()), deltaYHalf + Math.min(targetHeight, source.getHeight())); int dstX = (targetWidth - src.width()) / 2; int dstY = (targetHeight - src.height()) / 2; Rect dst = new Rect(dstX, dstY, targetWidth - dstX, targetHeight - dstY); c.drawBitmap(source, src, dst, null); if (recycle) { source.recycle(); } c.setBitmap(null); return b2; } float bitmapWidthF = source.getWidth(); float bitmapHeightF = source.getHeight(); float bitmapAspect = bitmapWidthF / bitmapHeightF; float viewAspect = (float) targetWidth / targetHeight; if (bitmapAspect > viewAspect) { float scale = targetHeight / bitmapHeightF; if (scale < .9F || scale > 1F) { scaler.setScale(scale, scale); } else { scaler = null; } } else { float scale = targetWidth / bitmapWidthF; if (scale < .9F || scale > 1F) { scaler.setScale(scale, scale); } else { scaler = null; } } Bitmap b1; if (scaler != null) { // this is used for minithumb and crop, so we want to filter here. b1 = Bitmap.createBitmap(source, 0, 0, source.getWidth(), source.getHeight(), scaler, true); } else { b1 = source; } if (recycle && b1 != source) { source.recycle(); } int dx1 = Math.max(0, b1.getWidth() - targetWidth); int dy1 = Math.max(0, b1.getHeight() - targetHeight); Bitmap b2 = Bitmap.createBitmap(b1, dx1 / 2, dy1 / 2, targetWidth, targetHeight); if (b2 != b1) { if (recycle || b1 != source) { b1.recycle(); } } return b2; } }