有没有任何方法或外部库可以在 Android 下使用 Lanczos（最好）或至少是双立方算法来调整图像大小？（当然，更快的处理速度更好，但质量是首要考虑因素，处理时间是次要的）
到目前为止，我所拥有的一切就是这些：
Bitmap resized = Bitmap.createScaledBitmap(yourBitmap, newWidth, newHeight, true);
然而，它使用双线性过滤器，输出质量很差。特别是如果您想要保留细节（如细线或可读文本）。
有许多优秀的Java库，例如在此处讨论的： Java - 调整图像大小而不失去质量
但是它总是依赖于Java awt类，例如java.awt.image.BufferedImage，因此无法在Android中使用。
是否有一种方法可以更改Bitmap.createScaledBitmap()方法中的默认（双线性）滤波器或类似于 Morten Nobel的库的库，该库能够与android.graphics.Bitmap类（或某些原始表示形式，正如@Tron在评论中所指出的）一起使用？
Bitmap缓冲区，您可以使用jnigraphics。这种方法保证了良好的性能和可靠的结果。uint8_t *src_data[4], *dst_data[4]; 来进行数据处理，因此可以使用 Bitmap.getPixels()+.setPixels()（在Android中）和java.awt.image.PixelGrabber（在awt环境中）轻松实现。这是一个悖论，但在Java环境中，最好的“平台无关”解决方案是在这里用C编写的。 - QuarkBitmap缓冲区比通过setPixels()复制/转换更有效，并且涉及较少的JNI特定代码。因此，它应该更容易阅读和理解。无论如何，其他人可能能够适应AWT的代码，甚至可以制作统一的代码。 - Sergio很不幸，Android使用android.graphics.Bitmap，而在Java中不存在该类，而Java使用java.awt.image.BufferedImage，而在Android中不存在 :-(
我没有一个可以直接使用的Android库，但我有一条路径，可以将一个特定于java-awt的库移植到平台无关的java库，并为Android和awt/j2se实现平台特定的处理程序。
在Java重缩放库中，您必须将所有特定于java-awt的类（如BufferedImage）隐藏在接口IBitmap后面，并为j2se和Android分别实现该接口。
我已经成功地完成了exif / icc / ipc元数据处理，并实现了接口pixymeta-lib/.../IBitmap.java，并为j2se pixymeta-j2se-lib/.../j2se/BitmapNative.java和android pixymeta-android-lib/.../android/BitmapNative.java提供了实现。IBitmap接口的平台无关库IBitmap的AWT/J2SE实现IBitmap的Android实现我最近写了一个程序将图像缩放/裁剪到特定分辨率并进行压缩处理:
public static void scaleImageToResolution(Context context, File image, int dstWidth, int dstHeight) {
if (dstHeight > 0 && dstWidth > 0 && image != null) {
Bitmap result = null;
try {
//Get Image Properties
BitmapFactory.Options bmOptions = new BitmapFactory.Options();
bmOptions.inJustDecodeBounds = true;
BitmapFactory.decodeFile(image.getAbsolutePath(), bmOptions);
int photoH = bmOptions.outHeight;
int photoW = bmOptions.outWidth;
bmOptions.inJustDecodeBounds = false;
bmOptions.inPurgeable = true;
//Smaller Image Size in Memory with Config
bmOptions.inPreferredConfig = Bitmap.Config.RGB_565;
//Is resolution not the same like 16:9 == 4:3 then crop otherwise fit
ScalingLogic scalingLogic = getScalingLogic(photoW, photoH,dstWidth, dstHeight);
//Get Maximum automatic downscaling that it's still bigger then this requested resolution
bmOptions.inSampleSize = calculateScalingSampleSize(photoW, photoH, dstWidth, dstHeight, scalingLogic);
//Get unscaled Bitmap
result = BitmapFactory.decodeFile(image.getAbsolutePath(), bmOptions);
//Scale Bitmap to requested Resolution
result = scaleImageToResolution(context, result, scalingLogic);
if (result != null) {
//Save Bitmap with quality
saveImageWithQuality(context, result, image);
}
} finally {
//Clear Memory
if (result != null)
result.recycle();
}
}
}
public static void saveImageWithQuality(Bitmap bitmap, String path, int compressQuality) {
try {
FileOutputStream fOut;
fOut = new FileOutputStream(path);
bitmap.compress(Bitmap.CompressFormat.JPEG, compressQuality, fOut);
fOut.flush();
fOut.close();
} catch (IOException ex) {
if (Logger.getRootLogger() != null)
Logger.getRootLogger().error(ex);
else
Log.e("saveImageWithQuality", "Error while saving compressed Picture: " + ex.getMessage() + StringUtils.newLine() + ex.getStackTrace().toString());
}
}
public static void saveImageWithQuality(Context context, Bitmap bitmap, File file) {
saveImageWithQuality(bitmap, file.getAbsolutePath(), getCompressQuality());
}
public static void saveImageWithQuality(Context context, Bitmap bitmap, String path) {
saveImageWithQuality(bitmap, path, getCompressQuality());
}
private static int calculateScalingSampleSize(int srcWidth, int srcHeight, int dstWidth, int dstHeight, ScalingLogic scalingLogic) {
if (scalingLogic == ScalingLogic.FIT) {
final float srcAspect = (float) srcWidth / (float) srcHeight;
final float dstAspect = (float) dstWidth / (float) dstHeight;
if (srcAspect > dstAspect) {
return srcWidth / dstWidth;
} else {
return srcHeight / dstHeight;
}
} else {
final float srcAspect = (float) srcWidth / (float) srcHeight;
final float dstAspect = (float) dstWidth / (float) dstHeight;
if (srcAspect > dstAspect) {
return srcHeight / dstHeight;
} else {
return srcWidth / dstWidth;
}
}
}
private static Bitmap scaleImageToResolution(Context context, Bitmap unscaledBitmap, ScalingLogic scalingLogic, int dstWidth, int dstHeight) {
//Do Rectangle of original picture when crop
Rect srcRect = calculateSrcRect(unscaledBitmap.getWidth(), unscaledBitmap.getHeight(), dstWidth, dstHeight, scalingLogic);
//Do Rectangle to fit in the source rectangle
Rect dstRect = calculateDstRect(unscaledBitmap.getWidth(), unscaledBitmap.getHeight(), dstWidth, dstHeight, scalingLogic);
//insert source rectangle into new one
Bitmap scaledBitmap = Bitmap.createBitmap(dstRect.width(), dstRect.height(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(scaledBitmap);
canvas.drawBitmap(unscaledBitmap, srcRect, dstRect, new Paint(Paint.FILTER_BITMAP_FLAG));
//Recycle the unscaled Bitmap afterwards
unscaledBitmap.recycle();
return scaledBitmap;
}
private static Rect calculateSrcRect(int srcWidth, int srcHeight, int dstWidth, int dstHeight, ScalingLogic scalingLogic) {
if (scalingLogic == ScalingLogic.CROP) {
if (srcWidth >= srcHeight) {
//Horizontal
final float srcAspect = (float) srcWidth / (float) srcHeight;
final float dstAspect = (float) dstWidth / (float) dstHeight;
if (srcAspect < dstAspect || isResolutionEqual(srcAspect, dstAspect)) {
final int srcRectHeight = (int) (srcWidth / dstAspect);
final int scrRectTop = (srcHeight - srcRectHeight) / 2;
return new Rect(0, scrRectTop, srcWidth, scrRectTop + srcRectHeight);
} else {
final int srcRectWidth = (int) (srcHeight * dstAspect);
final int srcRectLeft = (srcWidth - srcRectWidth) / 2;
return new Rect(srcRectLeft, 0, srcRectLeft + srcRectWidth, srcHeight);
}
} else {
//Vertikal
final float srcAspect = (float) srcHeight / (float) srcWidth;
final float dstAspect = (float) dstWidth / (float) dstHeight;
if (srcAspect < dstAspect || isResolutionEqual(srcAspect, dstAspect)) {
final int srcRectWidth = (int) (srcHeight / dstAspect);
final int srcRectLeft = (srcWidth - srcRectWidth) / 2;
return new Rect(srcRectLeft, 0, srcRectLeft + srcRectWidth, srcHeight);
} else {
final int srcRectHeight = (int) (srcWidth * dstAspect);
final int scrRectTop = (srcHeight - srcRectHeight) / 2;
return new Rect(0, scrRectTop, srcWidth, scrRectTop + srcRectHeight);
}
}
} else {
return new Rect(0, 0, srcWidth, srcHeight);
}
}
private static Rect calculateDstRect(int srcWidth, int srcHeight, int dstWidth, int dstHeight, ScalingLogic scalingLogic) {
if (scalingLogic == ScalingLogic.FIT) {
if (srcWidth > srcHeight) {
//Vertikal
final float srcAspect = (float) srcWidth / (float) srcHeight;
final float dstAspect = (float) dstWidth / (float) dstHeight;
if (srcAspect < dstAspect || isResolutionEqual(srcAspect, dstAspect)) {
return new Rect(0, 0, (int) (dstHeight * srcAspect), dstHeight);
} else {
return new Rect(0, 0, dstWidth, (int) (dstWidth / srcAspect));
}
} else {
//Horizontal
final float srcAspect = (float) srcHeight / (float) srcWidth;
final float dstAspect = (float) dstWidth / (float) dstHeight;
if (srcAspect < dstAspect || isResolutionEqual(srcAspect, dstAspect)) {
return new Rect(0, 0, (int) (dstHeight / srcAspect), dstHeight);
} else {
return new Rect(0, 0, dstWidth, (int) (dstWidth * srcAspect));
}
}
} else {
if (srcWidth >= srcHeight)
return new Rect(0, 0, dstWidth, dstHeight);
else
return new Rect(0, 0, dstHeight, dstWidth);
}
}
private static ScalingLogic getScalingLogic(int imageWidth, int imageHeight, int dstResolutionWidth, int dstResolutionHeight) {
if (imageWidth >= imageHeight) {
//Bild horizontal
final float srcAspect = (float) imageWidth / (float) imageHeight;
final float dstAspect = (float) dstResolutionWidth / (float) dstResolutionHeight;
if (!isResolutionEqual(srcAspect, dstAspect)) {
return ScalingLogic.CROP;
} else {
return ScalingLogic.FIT;
}
} else {
//Bild vertikal
final float srcAspect = (float) imageHeight / (float) imageWidth;
final float dstAspect = (float) dstResolutionWidth / (float) dstResolutionHeight;
if (!isResolutionEqual(srcAspect, dstAspect)) {
return ScalingLogic.CROP;
} else {
return ScalingLogic.FIT;
}
}
}
public enum PictureQuality {
High,
Medium,
Low
}
public enum ScalingLogic {
CROP,
FIT
}
//Does resolution match
private static boolean isResolutionEqual(float v1, float v2) {
// Falls a 1.999999999999 and b = 2.000000000000
return v1 == v2 || Math.abs(v1 - v2) / Math.max(Math.abs(v1), Math.abs(v2)) < 0.01;
}
public int getCompressQuality() {
if (Quality == PictureQuality.High)
return 100;
else if (Quality == PictureQuality.Medium)
return 50;
else if (Quality == PictureQuality.Low)
return 25;
else return 0;
}
它没有使用你提到的库，但它可以工作，我很满意。也许你也会喜欢。
这里是我用来调整图像大小的代码...
Bitmap photo1 ;
private byte[] imageByteArray1 ;
BitmapFactory.Options opt1 = new BitmapFactory.Options();
opt1.inJustDecodeBounds=true;
BitmapFactory.decodeFile(imageUrl.get(imgCount).toString(),opt1);
// The new size we want to scale to
final int REQUIRED_SIZE=320;
// Find the correct scale value. It should be the power of 2.
int width_tmp=opt1.outWidth,height_tmp=opt1.outHeight;
int scale=2;
while(true){
if(width_tmp>REQUIRED_SIZE||height_tmp>REQUIRED_SIZE)
break;
width_tmp/=2;
height_tmp/=2;
scale*=2;
}
// Decode with inSampleSize
BitmapFactory.Options o2=new BitmapFactory.Options();
o2.inSampleSize=scale;
o2.inJustDecodeBounds=false;
photo1=BitmapFactory.decodeFile(imageUrl.get(imgCount).toString(),o2);
ByteArrayOutputStream baos1=new ByteArrayOutputStream();
photo1.compress(Bitmap.CompressFormat.JPEG,60,baos1);
imageByteArray1=baos1.toByteArray();
如果您只是想以优化显示为目的重采样图像，您可以使用这个小巧玲珑的一行代码，它为我服务良好。
Bitmap bitmap = new BitmapDrawable(getResources(), yourBitmap).getBitmap();
这行代码可能看起来很奇怪，因为你正在将位图转换为BitmapDrawable，然后再次转换回位图，但是BitmapDrawable默认为设备的像素密度（除非您使用不同的构造函数）。
如果您还需要调整大小，则只需将其分成两行，并在将BitmapDrawable转换回位图之前使用setBounds，如下所示：
BitmapDrawable bitmapDrawable = new BitmapDrawable(getResources(), yourBitmap);
bitmapDrawable.setBounds(left, top, right, bottom); //Make it a new size in pixels.
yourBitmap = bitmapDrawable.getBitmap(); //Convert it back to a bitmap optimised for display purposes.
Bitmap drawable 可能被列为已弃用，但实际上只有某些构造函数被弃用了，而上面示例中的构造函数并没有被弃用。此外，这将与 API 4 兼容。
或者，Android 文档中有一个可下载的示例，您可以在此处找到：https://developer.android.com/topic/performance/graphics/load-bitmap.html
希望这可以帮助您。
Bitmap使用Paint： https://developer.android.com/reference/android/graphics/Paint （查找FILTER_BITMAP_FLAG- 启用缩放位图的双线性采样的 Paint 标志。） - Jolinar