问题
I'm using this compression class from the following site: http://voidcanvas.com/whatsapp-like-image-compression-in-android/
Here is my compression class with very little modifications from the original class:
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.media.ExifInterface;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import timber.log.Timber;
//http://voidcanvas.com/whatsapp-like-image-compression-in-android/
public class ImageCompressor {
public ImageCompressor() {}
public static String compressImage(String imagePath, Context context) {
Bitmap scaledBitmap = null;
String filename = "compressed_" +imagePath.substring(imagePath.lastIndexOf("/")+1);
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;
Timber.e( "imagePath "+imagePath);
Timber.e("filename "+filename);
Bitmap bmp = BitmapFactory.decodeFile(imagePath, options);
if (options == null) {
Timber.e("zero bitmap");
}
int actualHeight = options.outHeight;
int actualWidth = options.outWidth;
float imgRatio = actualWidth / actualHeight;
float maxHeight = actualHeight * 10/20;
float maxWidth = actualWidth * 10/20;
float maxRatio = maxWidth / 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(imagePath, 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(imagePath);
int orientation = exif.getAttributeInt(
ExifInterface.TAG_ORIENTATION, 0);
Timber.e("Exif: " + orientation);
Matrix matrix = new Matrix();
if (orientation == 6) {
matrix.postRotate(90);
Timber.e( "Exif: " + orientation);
} else if (orientation == 3) {
matrix.postRotate(180);
Timber.e( "Exif: " + orientation);
} else if (orientation == 8) {
matrix.postRotate(270);
Timber.e( "Exif: " + orientation);
}
scaledBitmap = Bitmap.createBitmap(scaledBitmap, 0, 0,
scaledBitmap.getWidth(), scaledBitmap.getHeight(), matrix,
true);
} catch (IOException e) {
e.printStackTrace();
} catch (NullPointerException e) {
e.printStackTrace();
}
FileOutputStream out = null;
try {
out = context.openFileOutput(filename, Context.MODE_PRIVATE);
scaledBitmap.compress(Bitmap.CompressFormat.JPEG, 90, out);
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return filename;
}
public static 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;
}
}
}
This is my original image:
This is my compressed image:
I don't understand why the compressed image has a black outline on the top and left hand side of the image. It only seems to happen with low res images; if it was a photo from a cellphone camera, this will tend to not happen as that is a high res image. If it was a low res photo from the internet, this will happen.
Does anyone know how I can fix this?
EDIT:
To test this, you can download the demo project here or create your own: http://www.voidcanvas.com/projects/1951EfficientImageLoading.zip You will need to navigate in your phone or emulator browser to a photo from Google Images and try to compress it. The result looks like the below, you can see the black borders appearing on the left and right sides:
回答1:
I believe the problem comes from this line:
canvas.drawBitmap(bmp, middleX - bmp.getWidth() / 2, middleY - bmp.getHeight() / 2, new Paint(Paint.FILTER_BITMAP_FLAG));
You're losing the precision by dividing by the integer 2.
try something like this:
canvas.drawBitmap(bmp, middleX - (float)bmp.getWidth() / 2.0f, middleY - (float)bmp.getHeight() / 2.0f, new Paint(Paint.FILTER_BITMAP_FLAG));
来源：https://stackoverflow.com/questions/36814555/android-compressing-images-creates-black-borders-on-left-and-top-margin