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
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…
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
我不知道我的解决方案是否是最佳实践，但我通过使用inDensity和inTargetDensity选项实现了加载我所需缩放的位图。当不加载可绘制资源时，inDensity初始值为0，因此此方法用于加载非资源图像。
变量imageUri, maxImageSideLength和context是我的方法的参数。为了清晰起见，我只发布了方法实现，没有包装AsyncTask。
ContentResolver resolver = context.getContentResolver();
InputStream is;
try {
is = resolver.openInputStream(imageUri);
} catch (FileNotFoundException e) {
Log.e(TAG, "Image not found.", e);
return null;
}
Options opts = new Options();
opts.inJustDecodeBounds = true;
BitmapFactory.decodeStream(is, null, opts);
// scale the image
float maxSideLength = maxImageSideLength;
float scaleFactor = Math.min(maxSideLength / opts.outWidth, maxSideLength / opts.outHeight);
// do not upscale!
if (scaleFactor < 1) {
opts.inDensity = 10000;
opts.inTargetDensity = (int) ((float) opts.inDensity * scaleFactor);
}
opts.inJustDecodeBounds = false;
try {
is.close();
} catch (IOException e) {
// ignore
}
try {
is = resolver.openInputStream(imageUri);
} catch (FileNotFoundException e) {
Log.e(TAG, "Image not found.", e);
return null;
}
Bitmap bitmap = BitmapFactory.decodeStream(is, null, opts);
try {
is.close();
} catch (IOException e) {
// ignore
}
return bitmap;
在阅读了这些答案和android文档后，以下是调整位图大小的代码，而无需将其加载到内存中:
public Bitmap getResizedBitmap(int targetW, int targetH, String imagePath) {
// Get the dimensions of the bitmap
BitmapFactory.Options bmOptions = new BitmapFactory.Options();
//inJustDecodeBounds = true <-- will not load the bitmap into memory
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);
return(bitmap);
}
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);
}
