如何在 Android 中模糊图像的某些部分?

做几次蒙版模糊....

do a masked blur few times ....

1. 创建蒙版

0 表示模糊(黑色)，>=1 表示不模糊(白色).将此部分初始化为足够大的值，例如 w=100 像素

0 means blur (black) and >=1 means not blur (white). Init this part by big enough value for example w=100 pixels

创建蒙版模糊功能

只是一个带有一些矩阵的普通卷积

just a common convolution with some matrix like

0.0 0.1 0.0
0.1 0.6 0.1
0.0 0.1 0.0

但仅对蒙版为 ==0 的目标像素执行此操作，在图像模糊后，蒙版也会模糊.这应该会稍微扩大白色区域(每次迭代按像素，但在边界上会损失幅度，这就是 w>1 的原因).

but do it only for target pixels where mask is ==0 after image is blurred blur also the mask. This should enlarge the white area a bit (by pixel per iteration but losing magnitude on borders that is why w>1).

循环子弹 #2 N 次

loop bullet #2 N times

N 确定模糊/非模糊渐变深度 w 只是为了确保毛刺蒙版会增长......每次模糊蒙版都会增加其白色部分

N determines blur/non-blur gradient depth the w is only to assure that burred mask will grow... Each time the blur mask will increase its white part

这应该可以解决问题，您还可以使用遮罩的扩张而不是模糊它.

That should do the trick, You can also use dilatation of the mask instead of blurring it.

[edit1] 实施

今天玩了一会儿，发现蒙版不够平滑，所以我稍微改变了算法(这里是我的代码 C++):

Have played with this a bit today and found out that the mask is not growing enough with smooth so I change the algo a bit (here mine code C++):

picture pic0,pic1,pic2;
    // pic0 - source
    // pic1 - output
    // pic2 - mask
int x0=400,y0=330,r0=100,dr=200;
    // x0,y0,r0 - masked area
    // dr - blur gradient size
int i,r;

// init output as sourceimage
pic1=pic0;
// init mask (size of source image) with gradient circles
pic2.resize(pic0.xs,pic0.ys);
pic2.clear(0);
for (i=1;i<=255;i++)
    {
    r=r0+dr-((dr*i)>>8);
    pic2.bmp->Canvas->Brush->Color=TColor(i<<16); // shifted because GDI has inverse channel layout then direct pixel access
    pic2.bmp->Canvas->Pen  ->Color=TColor(i<<16);
    pic2.bmp->Canvas->Ellipse(x0-r,y0-r,x0+r,y0+r);
    }
for (i=1;i<255;i+=10) pic1.rgb_smooth_masked(pic2,i);

这里是平滑函数:

//---------------------------------------------------------------------------
void picture::rgb_smooth_masked(const picture &mask,DWORD treshold)
    {
    int i,x,y;
    color *q0,*q1,*m0,c0,c1,c2;
    if ((xs<2)||(ys<2)) return;
    for (y=0;y<ys-1;y++)
        {
        q0=p[y  ]; m0=mask.p[y];
        q1=p[y+1];
        for (x=0;x<xs-1;x++)
         if (m0[x].dd<treshold)
            {
            c0=q0[x];
            c1=q0[x+1];
            c2=q1[x];
            for (i=0;i<4;i++)
             q0[x].db[i]=DWORD((DWORD(c0.db[i])+DWORD(c0.db[i])+DWORD(c1.db[i])+DWORD(c2.db[i]))>>2);
            }
        }
    }
//---------------------------------------------------------------------------

1. 创建渐变蒙版，圆圈的颜色从 1 增加到 255

1. create gradient mask with circles increasing in color from 1 to 255

rest 为黑色渐变宽度为 dr 并确定平滑锐度.

rest is black the gradient width is dr and determine the smoothing sharpness.

使用蒙版和阈值创建平滑蒙版

平滑掩码像素小于等于的所有像素临界点.请参阅函数 rgb_smooth_masked.它使用2x2卷积矩阵

smooth all pixels where mask pixel is < threshold. See the function rgb_smooth_masked. It uses 2x2 convolution matrix

0.50,0.25
0.25,0.00