有没有人知道如何在不损失图像质量的情况下缩放位图图像？目前我面临这个problem，其中所选图像的大小可能太大导致应用程序返回到另一个活动。
所以现在我尝试使用此方法缩放所选图像而不会降低其质量。我从here获得了代码。
protected void onActivityResult(int requestCode, int resultCode,
Intent data) {
super.onActivityResult(requestCode, resultCode, data);
switch (requestCode) {
case RESULT_LOAD_IMAGE:
if (requestCode == RESULT_LOAD_IMAGE && resultCode == RESULT_OK & null != data) {
Uri selectedImage = data.getData();
String[] filePathColumn = {MediaStore.Images.Media.DATA};
Cursor cursor = getContentResolver()
.query(selectedImage, filePathColumn, null, null,
null);
cursor.moveToFirst();
int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
String picturePath = cursor.getString(columnIndex);
cursor.close();
Bitmap a = (BitmapFactory.decodeFile(picturePath));
photo = scaleBitmap(a, 200, 200);
imageView.setImageBitmap(photo);
}
break;
}
public static Bitmap scaleBitmap(Bitmap bitmap, int newWidth, int newHeight) {
Bitmap scaledBitmap = Bitmap.createBitmap(newWidth, newHeight, Bitmap.Config.ARGB_8888);
float scaleX = newWidth / (float) bitmap.getWidth();
float scaleY = newHeight / (float) bitmap.getHeight();
float pivotX = 0;
float pivotY = 0;
Matrix scaleMatrix = new Matrix();
scaleMatrix.setScale(scaleX, scaleY, pivotX, pivotY);
Canvas canvas = new Canvas(scaledBitmap);
canvas.setMatrix(scaleMatrix);
canvas.drawBitmap(bitmap, 0, 0, new Paint(Paint.FILTER_BITMAP_FLAG));
return scaledBitmap;
}
答案似乎对大多数人有帮助，但为什么它对我不起作用？我错过了什么吗？
答案 0 :(得分：1)
请试试这个
public Bitmap scaleBitmap(Bitmap bitmap,int newWidth,int newHeight) {
Bitmap scaledBitmap = Bitmap.createBitmap(newWidth, newHeight, Config.ARGB_8888);
float ratioX = newWidth / (float) bitmap.getWidth();
float ratioY = newHeight / (float) bitmap.getHeight();
float middleX = newWidth / 2.0f;
float middleY = newHeight / 2.0f;
Matrix scaleMatrix = new Matrix();
scaleMatrix.setScale(ratioX, ratioY, middleX, middleY);
Canvas canvas = new Canvas(scaledBitmap);
canvas.setMatrix(scaleMatrix);
canvas.drawBitmap(bitmap, middleX - bitmap.getWidth() / 2, middleY - bitmap.getHeight() / 2, new Paint(Paint.FILTER_BITMAP_FLAG));
return scaledBitmap;
}
答案 1 :(得分：1)
尝试使用此缩放位图
public static Bitmap scaleBitmap(Bitmap bitmap, int newWidth, int newHeight) {
float scaleX = ((float)newWidth) / bitmap.getWidth();
float scaleY = ((float)newHeight) / bitmap.getHeight();
Matrix scaleMatrix = new Matrix();
scaleMatrix.postScale(scaleX, scaleY);
Bitmap scaledBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight() , scaleMatrix, true);
return scaledBitmap;
}
答案 2 :(得分：1)
Use this it will definitely help you to reduce the size without loosing quality.
public Bitmap compressImage(String imageUri) {
String filePath = imageUri;
// String filePath = getRealPathFromURI(imageUri);
Bitmap scaledBitmap = null;
BitmapFactory.Options options = new BitmapFactory.Options();
// by setting this field as true, the actual bitmap pixels are not
// loaded in the memory. Just the bounds are loaded. If
// you try the use the bitmap here, you will get null.
options.inJustDecodeBounds = true;
Bitmap bmp = BitmapFactory.decodeFile(filePath, options);
int actualHeight = options.outHeight;
int actualWidth = options.outWidth;
// max Height and width values of the compressed image is taken as
// 816x612
/*
* float maxHeight = 816.0f; float maxWidth = 612.0f;
*/
float maxHeight = 1080.0f;
float maxWidth = 800.0f;
float imgRatio = actualWidth / (float) actualHeight;
float maxRatio = maxWidth / (float) maxHeight;
// width and height values are set maintaining the aspect ratio of the
// image
if (actualHeight > maxHeight || actualWidth > maxWidth) {
if (imgRatio < maxRatio) {
imgRatio = maxHeight / actualHeight;
actualWidth = (int) (imgRatio * actualWidth);
actualHeight = (int) maxHeight;
} else if (imgRatio > maxRatio) {
imgRatio = maxWidth / actualWidth;
actualHeight = (int) (imgRatio * actualHeight);
actualWidth = (int) maxWidth;
} else {
actualHeight = (int) maxHeight;
actualWidth = (int) maxWidth;
}
}
// setting inSampleSize value allows to load a scaled down version of
// the original image
options.inSampleSize = calculateInSampleSize(options, actualWidth, actualHeight);
// inJustDecodeBounds set to false to load the actual bitmap
options.inJustDecodeBounds = false;
// this options allow android to claim the bitmap memory if it runs low
// on memory
options.inPurgeable = true;
options.inInputShareable = true;
options.inTempStorage = new byte[16 * 1024];
try {
// load the bitmap from its path
bmp = BitmapFactory.decodeFile(filePath, options);
} catch (OutOfMemoryError exception) {
exception.printStackTrace();
}
try {
scaledBitmap = Bitmap.createBitmap(actualWidth, actualHeight, Bitmap.Config.ARGB_8888);
} catch (OutOfMemoryError exception) {
exception.printStackTrace();
}
float ratioX = actualWidth / (float) options.outWidth;
float ratioY = actualHeight / (float) options.outHeight;
float middleX = actualWidth / 2.0f;
float middleY = actualHeight / 2.0f;
Matrix scaleMatrix = new Matrix();
scaleMatrix.setScale(ratioX, ratioY, middleX, middleY);
Canvas canvas = new Canvas(scaledBitmap);
canvas.setMatrix(scaleMatrix);
canvas.drawBitmap(bmp, middleX - bmp.getWidth() / 2, middleY - bmp.getHeight() / 2, new Paint(Paint.FILTER_BITMAP_FLAG));
// check the rotation of the image and display it properly
ExifInterface exif;
try {
exif = new ExifInterface(filePath);
int orientation = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION, 0);
displayLogs("EXIF", "Exif: " + orientation);
Matrix matrix = new Matrix();
if (orientation == 6) {
matrix.postRotate(90);
displayLogs("EXIF", "Exif: " + orientation);
} else if (orientation == 3) {
matrix.postRotate(180);
displayLogs("EXIF", "Exif: " + orientation);
} else if (orientation == 8) {
matrix.postRotate(270);
displayLogs("EXIF", "Exif: " + orientation);
}
scaledBitmap = Bitmap.createBitmap(scaledBitmap, 0, 0, scaledBitmap.getWidth(), scaledBitmap.getHeight(), matrix, true);
} catch (IOException e) {
e.printStackTrace();
}
FileOutputStream out = null;
String filename = getFilename(filePath);
// File image = new File(getFilename(), System.currentTimeMillis() +
// ".jpg");
try {
out = new FileOutputStream(filename);
// write the compressed bitmap at the destination specified by
// filename.
boolean didWrite = scaledBitmap.compress(Bitmap.CompressFormat.JPEG, 80, out);
out.close();
System.out.println(didWrite);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return scaledBitmap;
}
private String getRealPathFromURI(String contentURI) {
Uri contentUri = Uri.parse(contentURI);
Cursor cursor = getContentResolver().query(contentUri, null, null, null, null);
if (cursor == null) {
return contentUri.getPath();
} else {
cursor.moveToFirst();
int index = cursor.getColumnIndex(MediaStore.Images.ImageColumns.DATA);
return cursor.getString(index);
}
}
public int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
final int heightRatio = Math.round((float) height / (float) reqHeight);
final int widthRatio = Math.round((float) width / (float) reqWidth);
inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
}
final float totalPixels = width * height;
final float totalReqPixelsCap = reqWidth * reqHeight * 2;
while (totalPixels / (inSampleSize * inSampleSize) > totalReqPixelsCap) {
inSampleSize++;
}
return inSampleSize;
}
public String getFilename(String originalname) {
ImageCache imageCache = new ImageCache(this);
File file = new File("Your folder path");
// return file;
String uriSting = (file.getAbsolutePath() + "/" + "F_" + System.currentTimeMillis() + ".png");
return uriSting;
}
答案 3 :(得分：0)
您的问题是您没有保持原始图像的宽高比。 在你的代码中，如果你需要宽度为200，那么高度应该像这样计算：
newHeight = ((float) originalHeight/(float) originalWidth) * (float) newWidth;
所以在你的情况下：
float newHeight = ((float) a.getHeight()/(float) a.getWidth()) * (float) 200;
然后使用width:200调用缩放函数，并根据原始值计算高度。
之后如果质量仍然很低，那么尝试增加宽度并在获得所需质量时停止。
答案 4 :(得分：-1)
当你有太多的大图像时，你必须要管理Bitmap缓存策略.Bitmap缓存管理太复杂了。所以在Android中我们有一个极好的库Picasso。这个库提供内置缓存管理。这将在后台管理您的位图，它还提供图像缓存功能。在您的图像加载后再次加载相同的图像，这将在缓存中获取。内置功能无需更改在代码中。
我希望你清楚我的解决方案。 最好的运气