Tip---数据类型占位-&-降采样-&-像素读取-&-Bitmap-&-Color源码

Mat与Bitmap Mat像素操作 C语言数据类型占位

#数据类型占位 **byte = 8bit；**
#降采样（图片压缩）  ``` private void displaySelectedImage() { if(fileUri == null) return; ImageView imageView = (ImageView)this.findViewById(R.id.sample_img);

    BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;

    BitmapFactory.decodeFile(fileUri.getPath(), options);
    int w = options.outWidth;
    int h = options.outHeight;
    int inSample = 1;
    if(w > 1000 || h > 1000) {
        while(Math.max(w/inSample, h/inSample) > 1000) {
            inSample *=2;
        }
    }

    options.inJustDecodeBounds = false;
    options.inSampleSize = inSample;
    options.inPreferredConfig = Bitmap.Config.ARGB_8888;

    Bitmap bm = BitmapFactory.decodeFile(fileUri.getPath(), options);
    imageView.setImageBitmap(bm);
}

<br>
#Bitmap的API
![](https://p3-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/e1c55d9c20dd406d8bea9b847539c701~tplv-k3u1fbpfcp-zoom-1.image)![](https://p3-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/e9bb97e9373e4b638f43315ab6395fc5~tplv-k3u1fbpfcp-zoom-1.image)


<br>
#Color的源码
![](https://p3-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/8bcfffe28183492085f08ff5b2f71efe~tplv-k3u1fbpfcp-zoom-1.image)

@ColorInt
public static int rgb(float red, float green, float blue) {
    return 0xff000000 |
           ((int) (red   * 255.0f + 0.5f) << 16) |
           ((int) (green * 255.0f + 0.5f) <<  8) |
            (int) (blue  * 255.0f + 0.5f);
}

---

@ColorInt
public static int rgb(
        @IntRange(from = 0, to = 255) int red,
        @IntRange(from = 0, to = 255) int green,
        @IntRange(from = 0, to = 255) int blue) {
    return 0xff000000 | (red << 16) | (green << 8) | blue;
}

---

@IntRange(from = 0, to = 255)
public static int alpha(int color) {
    return color >>> 24;
}

---

@IntRange(from = 0, to = 255)
public static int red(int color) {
    return (color >> 16) & 0xFF;
}

---

@IntRange(from = 0, to = 255)
public static int green(int color) {
    return (color >> 8) & 0xFF;
}

---

@IntRange(from = 0, to = 255)
public static int blue(int color) {
    return color & 0xFF;
}

<br>
#ARGB_8888像素读取
一个像素数据量有32位大小，需要用int存储；

public void getBitmapInfo() { Bitmap bm = BitmapFactory.decodeResource(this.getResources(), R.drawable.lena); int width = bm.getWidth(); int height = bm.getHeight(); Bitmap.Config config = bm.getConfig();

    int a=0, r=0, g=0, b=0;
    for(int row=0; row<height; row++) {
        for(int col=0; col<width; col++) {
            // 读取像素
            int pixel = bm.getPixel(col, row);
            a = Color.alpha(pixel);
            r = Color.red(pixel);
            g = Color.green(pixel);
            b = Color.blue(pixel);
            // 修改像素
            r = 255 - r;
            g = 255 - g;
            b = 255 - b;
            // 保存到Bitmap中
            bm.setPixel(col, row, Color.argb(a, r, g, b));
        }
    }

![](https://p3-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/a43c530697c746c295b8eee0250eeb37~tplv-k3u1fbpfcp-zoom-1.image)下面修改通道的时候使用的是位运算，
其实对比Color源码我们知道这跟调用Color的API是一样的：

private void scanPixelsDemo() { Bitmap bm = BitmapFactory.decodeResource(this.getResources(), R.drawable.lena).copy(Bitmap.Config.ARGB_8888, true); int width = bm.getWidth(); int height = bm.getHeight(); Bitmap.Config config = bm.getConfig();

    int[] pixels = new int[width*height];
    bm.getPixels(pixels, 0, width, 0, 0, width, height);
    int a=0, r=0, g=0, b=0;
    int index = 0;
    for(int row=0; row<height; row++) {
        for(int col=0; col<width; col++) {
            // 读取像素
            index = width*row + col;
            a=(pixels[index]>>24)&0xff;
            r=(pixels[index]>>16)&0xff;
            g=(pixels[index]>>8)&0xff;
            b=pixels[index]&0xff;
            // 修改像素
            r = 255 - r;
            g = 255 - g;
            b = 255 - b;
            // 保存到Bitmap中
            pixels[index] = (a << 24) | (r << 16) | (g << 8) | b;
        }
    }

    bm.setPixels(pixels, 0, width, 0, 0, width, height);

    ImageView iv = (ImageView)this.findViewById(R.id.matInfo_imageView);
    iv.setImageBitmap(bm);
    bm.recycle();//释放内存！！！！！！！！

}

![](https://p3-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/e86eba45bff744c4975731c43c47c897~tplv-k3u1fbpfcp-zoom-1.image)


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#OpenCV中的Mat读法像素操作
**（一共 [三种](https://www.jianshu.com/p/232b6468f80a)，这里写的第一种）**

Mat src = Imgcodecs.imread(fileUri.getPath()); if(src.empty()){ 　　return; } int channels = src.channels(); int width = src.cols(); int height = src.rows();

byte[] data = new byte[channels]; int b=0, g=0, r=0; for(int row=0; row<height; row++) { 　　for(int col=0; col<width; col++) { 　　　　　　// 读取 　　　　　　src.get(row, col, data);//!!!!!!!!!!!!!!!!!!!!!!!读取一个px 　　　　　　b = data[0]&0xff; 　　　　　　g = data[1]&0xff; 　　　　　　r = data[2]&0xff; 　　　　　　// 修改 　　　　　　b = 255 - b; 　　　　　　g = 255 - g; 　　　　　　r = 255 - r; 　　　　　　// 写入 　　　　　　data[0] = (byte)b; 　　　　　　data[1] = (byte)g; 　　　　　　data[2] = (byte)r; 　　　　　　src.put(row, col, data); 　　} }