核心图在ios7中图像不缩放

Question

    UIImage *image = [UIImage imageNamed:@"tick_16.png"];
    CPTImage *background = [CPTImage imageWithCGImage:image.CGImage scale:image.scale];
    CPTBorderedLayer *imageLayer = [[CPTBorderedLayer alloc] initWithFrame:CGRectMake(0, 0, 16, 16)];
    imageLayer.fill = [CPTFill fillWithImage:background];
    CPTAxisLabel *iconLabel = [[CPTAxisLabel alloc] initWithContentLayer:imageLayer];
    iconLabel.offset = 8;
    iconLabel.tickLocation = CPTDecimalFromCGFloat(location+0.5);

图像在ios7中没有缩放。请给我解决方案。提前致谢