我在一个文件中有一个大的位图(比如3888x2592)。现在，我想将位图大小调整为800x533，并将其保存到另一个文件中。
我通常通过调用bitmap来缩放位图。createBitmap方法，但它需要一个源位图作为第一个参数，我不能提供，因为加载原始图像到位图对象当然会超过内存(例如，见这里)。
我也不能读取位图，例如，BitmapFactory.decodeFile(文件，选项)，提供BitmapFactory.Options。inSampleSize，因为我想把它调整到精确的宽度和高度。使用inSampleSize将位图大小调整为972x648(如果我使用inSampleSize=4)或778x518(如果我使用inSampleSize=5，这甚至不是2的幂)。
我还希望避免在第一步中使用inSampleSize读取图像，例如，在第一步中使用972x648，然后在第二步中将其大小调整为800x533，因为与直接调整原始图像的大小相比，质量会较差。
总结一下我的问题:
是否有一种方法来读取一个10MP或更多的大图像文件，并将其保存到一个新的图像文件，调整到一个特定的新宽度和高度，而不得到OutOfMemory异常?
我还尝试了BitmapFactory.decodeFile(文件，选项)和设置选项。out theight and Options。outidth值手动为800和533，但它不是这样工作的。
使用以下代码调整位图的大小
public static Bitmap decodeFile(File file, int reqWidth, int reqHeight){
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(file.getPath(), options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeFile(file.getPath(), options);
}
private static int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
// Calculate ratios of height and width to requested height and width
final int heightRatio = Math.round((float) height / (float) reqHeight);
final int widthRatio = Math.round((float) width / (float) reqWidth);
// Choose the smallest ratio as inSampleSize value, this will guarantee
// a final image with both dimensions larger than or equal to the
// requested height and width.
inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
}
return inSampleSize;
}
下面的提示/技巧也解释了这一点
http://www.codeproject.com/Tips/625810/Android-Image-Operations-Using-BitmapFactory
承认到目前为止另一个很好的答案，我所见过的最好的代码是在拍照工具的文档中。
请参阅“解码缩放图像”一节。
http://developer.android.com/training/camera/photobasics.html
它提出的解决方案是一个调整大小然后缩放的解决方案，就像这里的其他解决方案一样，但它非常简洁。
为了方便起见，我复制了下面的代码作为一个现成的函数。
private void setPic(String imagePath, ImageView destination) {
int targetW = destination.getWidth();
int targetH = destination.getHeight();
// Get the dimensions of the bitmap
BitmapFactory.Options bmOptions = new BitmapFactory.Options();
bmOptions.inJustDecodeBounds = true;
BitmapFactory.decodeFile(imagePath, bmOptions);
int photoW = bmOptions.outWidth;
int photoH = bmOptions.outHeight;
// Determine how much to scale down the image
int scaleFactor = Math.min(photoW/targetW, photoH/targetH);
// Decode the image file into a Bitmap sized to fill the View
bmOptions.inJustDecodeBounds = false;
bmOptions.inSampleSize = scaleFactor;
bmOptions.inPurgeable = true;
Bitmap bitmap = BitmapFactory.decodeFile(imagePath, bmOptions);
destination.setImageBitmap(bitmap);
}
上面的代码更简洁一些。InputStreams最终关闭了包装，以确保它们也被关闭:
*请注意
输入:InputStream is, int w, int h
输出:位图
try
{
final int inWidth;
final int inHeight;
final File tempFile = new File(temp, System.currentTimeMillis() + is.toString() + ".temp");
{
final FileOutputStream tempOut = new FileOutputStream(tempFile);
StreamUtil.copyTo(is, tempOut);
tempOut.close();
}
{
final InputStream in = new FileInputStream(tempFile);
final BitmapFactory.Options options = new BitmapFactory.Options();
try {
// decode image size (decode metadata only, not the whole image)
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(in, null, options);
}
finally {
in.close();
}
// save width and height
inWidth = options.outWidth;
inHeight = options.outHeight;
}
final Bitmap roughBitmap;
{
// decode full image pre-resized
final InputStream in = new FileInputStream(tempFile);
try {
final BitmapFactory.Options options = new BitmapFactory.Options();
// calc rought re-size (this is no exact resize)
options.inSampleSize = Math.max(inWidth/w, inHeight/h);
// decode full image
roughBitmap = BitmapFactory.decodeStream(in, null, options);
}
finally {
in.close();
}
tempFile.delete();
}
float[] values = new float[9];
{
// calc exact destination size
Matrix m = new Matrix();
RectF inRect = new RectF(0, 0, roughBitmap.getWidth(), roughBitmap.getHeight());
RectF outRect = new RectF(0, 0, w, h);
m.setRectToRect(inRect, outRect, Matrix.ScaleToFit.CENTER);
m.getValues(values);
}
// resize bitmap
final Bitmap resizedBitmap = Bitmap.createScaledBitmap(roughBitmap, (int) (roughBitmap.getWidth() * values[0]), (int) (roughBitmap.getHeight() * values[4]), true);
return resizedBitmap;
}
catch (IOException e) {
logger.error("Error:" , e);
throw new ResourceException("could not create bitmap");
}
我使用了这样的代码:
String filePath=Environment.getExternalStorageDirectory()+"/test_image.jpg";
BitmapFactory.Options options=new BitmapFactory.Options();
InputStream is=new FileInputStream(filePath);
BitmapFactory.decodeStream(is, null, options);
is.close();
is=new FileInputStream(filePath);
// here w and h are the desired width and height
options.inSampleSize=Math.max(options.outWidth/460, options.outHeight/288); //Max 460 x 288 is my desired...
// bmp is the resized bitmap
Bitmap bmp=BitmapFactory.decodeStream(is, null, options);
is.close();
Log.d(Constants.TAG, "Scaled bitmap bytes, "+bmp.getRowBytes()+", width:"+bmp.getWidth()+", height:"+bmp.getHeight());
我试过原始图像是1230 x 1230，得到的位图是330 x 330。
如果尝试2590 x 3849，我将得到OutOfMemoryError。
我跟踪了它，它仍然抛出OutOfMemoryError在行"BitmapFactory.decodeStream(is, null, options);"，如果原始位图太大…
贾斯汀的答案翻译成代码(对我来说很完美):
private Bitmap getBitmap(String path) {
Uri uri = getImageUri(path);
InputStream in = null;
try {
final int IMAGE_MAX_SIZE = 1200000; // 1.2MP
in = mContentResolver.openInputStream(uri);
// Decode image size
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(in, null, options);
in.close();
int scale = 1;
while ((options.outWidth * options.outHeight) * (1 / Math.pow(scale, 2)) >
IMAGE_MAX_SIZE) {
scale++;
}
Log.d(TAG, "scale = " + scale + ", orig-width: " + options.outWidth + ",
orig-height: " + options.outHeight);
Bitmap resultBitmap = null;
in = mContentResolver.openInputStream(uri);
if (scale > 1) {
scale--;
// scale to max possible inSampleSize that still yields an image
// larger than target
options = new BitmapFactory.Options();
options.inSampleSize = scale;
resultBitmap = BitmapFactory.decodeStream(in, null, options);
// resize to desired dimensions
int height = resultBitmap.getHeight();
int width = resultBitmap.getWidth();
Log.d(TAG, "1th scale operation dimenions - width: " + width + ",
height: " + height);
double y = Math.sqrt(IMAGE_MAX_SIZE
/ (((double) width) / height));
double x = (y / height) * width;
Bitmap scaledBitmap = Bitmap.createScaledBitmap(resultBitmap, (int) x,
(int) y, true);
resultBitmap.recycle();
resultBitmap = scaledBitmap;
System.gc();
} else {
resultBitmap = BitmapFactory.decodeStream(in);
}
in.close();
Log.d(TAG, "bitmap size - width: " +resultBitmap.getWidth() + ", height: " +
resultBitmap.getHeight());
return resultBitmap;
} catch (IOException e) {
Log.e(TAG, e.getMessage(),e);
return null;
}
