Android imageview从缩放图像中获取像素颜色

Question

我的家庭自动化应用程序有一个功能，人们可以将带有平面图和仪表板的图像上传到手机上，用以控制他们的家庭自动化软件。我让他们上传两张图像：一张是带有他们想要显示的图形的可见图像，另一张是与他们想要从可见图像中瞄准的对象相对应的纯色地图。两个图像必须具有相同的大小，按像素排列。当他们点击屏幕时，我希望能够从颜色图覆盖中获得颜色，然后我继续做与该颜色相关的任何操作。问题是，图像的缩放比例把我搞砸了。他们使用的图像可能比设备屏幕大，所以我对它们进行缩放，使它们适合显示。我现在并不真的需要缩放功能，但我以后可能会实现它。目前，我只希望图像以最大的尺寸显示，以便适合屏幕。所以，我的问题是，我如何修改这个代码，以便从缩放的图像中获得正确的接触点颜色。图像缩放本身似乎运行良好。它已按比例缩放并正确显示。我就是找不到合适的接触点。

final Bitmap bm = decodeSampledBitmapFromFile(visible_image, size, size);
if (bm!=null) {
imageview.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
imageview.setImageBitmap(bm);
}
final Bitmap bm2 = decodeSampledBitmapFromFile(image_overlay, size, size);
if (bm2!=null) {
overlayimageview.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
overlayimageview.setImageBitmap(bm2);
imageview.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent mev) {
DecodeActionDownEvent(v, mev, bm2);
return false;
}
});
}
private void DecodeActionDownEvent(View v, MotionEvent ev, Bitmap bm2)
{
xCoord = Integer.valueOf((int)ev.getRawX());
yCoord = Integer.valueOf((int)ev.getRawY());
try {
// Here's where the trouble is.
// returns the value of the unscaled pixel at the scaled touch point?
colorTouched = bm2.getPixel(xCoord, yCoord); 
} catch (IllegalArgumentException e) {
colorTouched = Color.WHITE; // nothing happens when touching white
}
}
private static Bitmap decodeSampledBitmapFromFile(String fileName, 
int reqWidth, int reqHeight) {
// code from 
// http://developer.android.com/training/displaying-bitmaps/load-bitmap.html
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(fileName, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeFile(fileName, options);
}
private static int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// code from 
// http://developer.android.com/training/displaying-bitmaps/load-bitmap.html
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
if (width > height) {
inSampleSize = Math.round((float)height / (float)reqHeight);
} else {
inSampleSize = Math.round((float)width / (float)reqWidth);
}
}
return inSampleSize;
}

Answer 1

我想明白了。我更换了

xCoord = Integer.valueOf((int)ev.getRawX());
yCoord = Integer.valueOf((int)ev.getRawY());

带有

Matrix inverse = new Matrix();
v.getImageMatrix().invert(inverse);
float[] touchPoint = new float[] {ev.getX(), ev.getY()};
inverse.mapPoints(touchPoint);
xCoord = Integer.valueOf((int)touchPoint[0]);
yCoord = Integer.valueOf((int)touchPoint[1]);

Answer 2

7年后，我必须提供另一个答案，因为从LG G6升级到LG G8s后，接受的答案中的代码停止返回正确的颜色。

这个解决方案适用于我在家里找到的所有手机，但谁知道呢。。。也许即使是这个也不是普遍的。

(使用Xamarin C#，但原理很容易理解)

首先，我们必须将实际的ImageView大小作为float来获得浮点除法

private float imageSizeX;
private float imageSizeY;
private void OnCreate(...) {
...
FindViewById<ImageView>(Resource.Id.colpick_Image).LayoutChange += OnImageLayout;
FindViewById<ImageView>(Resource.Id.colpick_Image).Touch += Image_Touch;
...
}
//Event called every time the layout of our ImageView is updated
private void OnImageLayout(object sender, View.LayoutChangeEventArgs e) {
imageSizeX = Image.Width;
imageSizeY = Image.Height;
Image.LayoutChange -= OnImageLayout; //Just need it once then unsubscribe
}

//Called every time user touches/is touching the ImageView
private void Image_Touch(object sender, View.TouchEventArgs e) {
MotionEvent m = e.Event;
ImageView img = sender as ImageView;
int x = Convert.ToInt32(m.GetX(0));
int y = Convert.ToInt32(m.GetY(0));
Bitmap bmp = (img.Drawable as BitmapDrawable).Bitmap;
// The scale value (how many times is the image bigger)
// I only use it with images where Width == Height, so I get
// scaleX == scaleY
float scaleX = bmp.Width / imageSizeX;
float scaleY = bmp.Height / imageSizeY;
x = (int)(x * scaleX);
y = (int)(y * scaleY);
// Check for invalid values/outside of image bounds etc...
// Get the correct Color ;)
int color = bmp.GetPixel(x, y);
}