是否有任何方法或外部库可以使用 Lanczos （理想情况下）或至少bicubic alg来调整图像大小。在 Android 下？ （当然，越快越好，但质量优先，处理时间是次要的）
到目前为止，我得到的一切都是：
Bitmap resized = Bitmap.createScaledBitmap(yourBitmap, newWidth, newHeight, true);
然而，它使用双线性滤波器，输出质量很差。特别是如果你想保留细节（如细线或可读文本）。
有很多适合Java的好库，例如这里讨论的： Java - resize image without losing quality
然而，它总是依赖于java.awt.image.BufferedImage之类的Java awt类，所以它不能在Android中使用。
有没有办法如何更改Bitmap.createScaledBitmap()方法中的默认（双线性）过滤器或某些库Morten Nobel's lib能够使用android.graphics.Bitmap类（或带有一些原始表示） ，正如@Tron在评论中所指出的那样）？
答案 0 :(得分：6)
最有前途的IMO是使用libswscale（来自FFmpeg），它提供Lanczos和许多其他过滤器。要从本机代码访问Bitmap缓冲区，您可以使用jnigraphics。这种方法可以保证良好的性能和可靠的结果。
修改
Here您可以找到使用提议方法的粗略演示应用。目前表现令人沮丧，因此应该对其进行调查，以决定是否采取措施改善它。
答案 1 :(得分：5)
不幸的是，Android使用了java中不存在的android.graphics.Bitmap 而java使用android中不存在的java.awt.image.BufferedImage： - （
我没有a ready to use library for android但是有一条路径如何将java-awt特定的lib移植到一个平台，独立于java lib，并使用了特定于android和awt / j2se的特定处理程序
在java rescale lib中，你必须隐藏接口IBitmap后面的所有java-awt特定类（如BufferedImage），并为j2se实现该接口，并为Android独立实现。
我已成功完成exif / icc / ipc元数据处理并实现了接口pixymeta-lib/.../IBitmap.java，并实现了j2se pixymeta-j2se-lib/.../j2se/BitmapNative.java和android pixymeta-android-lib/.../android/BitmapNative.java
所以我有这些包
IBitmap interface IBitmap IBitmap 答案 2 :(得分：0)
我最近写这篇文章是为了将图像缩放/裁剪为特定分辨率并按质量压缩它：
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;
}
它没有使用您提到的库，但它有效并且我很满意。也许你也是。
答案 3 :(得分：0)
以下是我用于调整图片大小的代码..
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();
希望它会帮助你..
答案 4 :(得分：0)
如果您只想以一种针对显示目的进行优化的方式对图像进行重新取样，您可以使用这款漂亮的小型衬垫，这对我来说很有用。
Bitmap bitmap = new BitmapDrawable(getResources(), yourBitmap).getBitmap();
这行代码可能看起来很奇怪，因为您将位图转换为BitmapDrawable并再次返回到位图，但BitmapDrawable默认为设备的像素密度（除非您使用不同的构造函数）。
如果你还需要调整大小，那么只需将它分成两行并使用setBounds，然后再将BitmapDrawable转换回如下位图：
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.
位图drawable可以列为depricated，但不是，只有某些构造函数被删除，上面例子中的构造函数没有被删除。这也适用于API 4
另外，Android文档在这里有一个可下载的示例：https://developer.android.com/topic/performance/graphics/load-bitmap.html
希望这有帮助。