iOS 上 UIImage 的运动模糊效果

Question

有没有办法在 UIImage 上获得运动模糊效果？ 我尝试了 GPUImage、Filtrr 和 iOS Core Image，但所有这些都有常规模糊 - 没有运动模糊。

我也尝试过 UIImage-DSP，但它的运动模糊几乎不可见。我需要更强大的东西。

Answer 1

正如我在存储库中评论的那样，我刚刚向 GPUImage 添加了运动和缩放模糊。这些是 GPUImageMotionBlurFilter 和 GPUImageZoomBlurFilter 类。这是缩放模糊的示例：

对于运动模糊，我在单个方向上进行 9-hit 高斯模糊。这是使用以下顶点和片段着色器实现的：

顶点：

 attribute vec4 position;
 attribute vec4 inputTextureCoordinate;

 uniform highp vec2 directionalTexelStep;

 varying vec2 textureCoordinate;
 varying vec2 oneStepBackTextureCoordinate;
 varying vec2 twoStepsBackTextureCoordinate;
 varying vec2 threeStepsBackTextureCoordinate;
 varying vec2 fourStepsBackTextureCoordinate;
 varying vec2 oneStepForwardTextureCoordinate;
 varying vec2 twoStepsForwardTextureCoordinate;
 varying vec2 threeStepsForwardTextureCoordinate;
 varying vec2 fourStepsForwardTextureCoordinate;

 void main()
 {
     gl_Position = position;

     textureCoordinate = inputTextureCoordinate.xy;
     oneStepBackTextureCoordinate = inputTextureCoordinate.xy - directionalTexelStep;
     twoStepsBackTextureCoordinate = inputTextureCoordinate.xy - 2.0 * directionalTexelStep;
     threeStepsBackTextureCoordinate = inputTextureCoordinate.xy - 3.0 * directionalTexelStep;
     fourStepsBackTextureCoordinate = inputTextureCoordinate.xy - 4.0 * directionalTexelStep;
     oneStepForwardTextureCoordinate = inputTextureCoordinate.xy + directionalTexelStep;
     twoStepsForwardTextureCoordinate = inputTextureCoordinate.xy + 2.0 * directionalTexelStep;
     threeStepsForwardTextureCoordinate = inputTextureCoordinate.xy + 3.0 * directionalTexelStep;
     fourStepsForwardTextureCoordinate = inputTextureCoordinate.xy + 4.0 * directionalTexelStep;
 }

片段：

 precision highp float;

 uniform sampler2D inputImageTexture;

 varying vec2 textureCoordinate;
 varying vec2 oneStepBackTextureCoordinate;
 varying vec2 twoStepsBackTextureCoordinate;
 varying vec2 threeStepsBackTextureCoordinate;
 varying vec2 fourStepsBackTextureCoordinate;
 varying vec2 oneStepForwardTextureCoordinate;
 varying vec2 twoStepsForwardTextureCoordinate;
 varying vec2 threeStepsForwardTextureCoordinate;
 varying vec2 fourStepsForwardTextureCoordinate;

 void main()
 {
     lowp vec4 fragmentColor = texture2D(inputImageTexture, textureCoordinate) * 0.18;
     fragmentColor += texture2D(inputImageTexture, oneStepBackTextureCoordinate) * 0.15;
     fragmentColor += texture2D(inputImageTexture, twoStepsBackTextureCoordinate) *  0.12;
     fragmentColor += texture2D(inputImageTexture, threeStepsBackTextureCoordinate) * 0.09;
     fragmentColor += texture2D(inputImageTexture, fourStepsBackTextureCoordinate) * 0.05;
     fragmentColor += texture2D(inputImageTexture, oneStepForwardTextureCoordinate) * 0.15;
     fragmentColor += texture2D(inputImageTexture, twoStepsForwardTextureCoordinate) *  0.12;
     fragmentColor += texture2D(inputImageTexture, threeStepsForwardTextureCoordinate) * 0.09;
     fragmentColor += texture2D(inputImageTexture, fourStepsForwardTextureCoordinate) * 0.05;

     gl_FragColor = fragmentColor;
 }

作为优化，我使用角度、模糊大小和图像尺寸来计算片段着色器外部纹理样本之间的步长。然后将其传递给顶点着色器，以便我可以在那里计算纹理采样位置并在片段着色器中对它们进行插值。这避免了在 iOS 设备上的依赖纹理读取。

缩放模糊要慢得多，因为我仍然在片段着色器中进行这些计算。毫无疑问，有一种方法可以优化它，但我还没有尝试过。缩放模糊使用 9-hit 高斯模糊，其中方向和每个样本的偏移距离随像素位置与模糊中心的关系而变化。

它使用以下片段着色器（和标准的直通顶点着色器）：

 varying highp vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;

 uniform highp vec2 blurCenter;
 uniform highp float blurSize;

 void main()
 {
     // TODO: Do a more intelligent scaling based on resolution here
     highp vec2 samplingOffset = 1.0/100.0 * (blurCenter - textureCoordinate) * blurSize;

     lowp vec4 fragmentColor = texture2D(inputImageTexture, textureCoordinate) * 0.18;
     fragmentColor += texture2D(inputImageTexture, textureCoordinate + samplingOffset) * 0.15;
     fragmentColor += texture2D(inputImageTexture, textureCoordinate + (2.0 * samplingOffset)) *  0.12;
     fragmentColor += texture2D(inputImageTexture, textureCoordinate + (3.0 * samplingOffset)) * 0.09;
     fragmentColor += texture2D(inputImageTexture, textureCoordinate + (4.0 * samplingOffset)) * 0.05;
     fragmentColor += texture2D(inputImageTexture, textureCoordinate - samplingOffset) * 0.15;
     fragmentColor += texture2D(inputImageTexture, textureCoordinate - (2.0 * samplingOffset)) *  0.12;
     fragmentColor += texture2D(inputImageTexture, textureCoordinate - (3.0 * samplingOffset)) * 0.09;
     fragmentColor += texture2D(inputImageTexture, textureCoordinate - (4.0 * samplingOffset)) * 0.05;

     gl_FragColor = fragmentColor;
 }

请注意，出于性能原因，这两种模糊都被硬编码为 9 个样本。这意味着在较大的模糊尺寸下，您将开始从此处的有限样本中看到伪影。对于较大的模糊，您需要多次运行这些过滤器或扩展它们以支持更多高斯样本。但是，由于 iOS 设备上的纹理采样带宽有限，更多的样本会导致渲染时间变慢。

Answer 2

CoreImage 有一个运动模糊滤镜。

它叫 CIMotionBlur...http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/CoreImageFilterReference/Reference/reference.html#//apple_ref/doc/filter/ci/CIMotionBlur