以下是我尝试应用以在图像上获取CIFourfoldRotatedTile过滤器的代码，但我在输出中得到的是nil图像。CIContext*context=[CIContextcontextWithOptions:nil];//1CIImage*aimage=[CIImageimageWithCGImage:[UIImageimageNamed:@"Image1.png"].CGImage];CIFilter*filter=[CIFilterfilterWithName:@"CIFourfoldRotatedTile"];//3[filtersetValue:aimageforKey:k