case 1 : 使用CIContext作為全局對象。渲染時一直報錯闰蛔。錯誤代碼如下：
if (ciContext == nil) { kCIContextOutputColorSpace : (__bridge id)rgbColorSpace}];
EAGLContext *eaglContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
ciContext = [CIContext contextWithEAGLContext:eaglContext options:@{kCIContextWorkingColorSpace : [NSNull null]}];
}
[ciContext render:ciImage toCVPixelBuffer:pixelBuffer bounds:cropRect colorSpace:nil];
cicontextError
