ios对图片进行缩小尺寸和透明度设置

#import "UIImage+XSScaleImage.h"

@implementation UIImage (XSScaleImage)
-(UIImage *)scaleImageWithSize:(CGSize)size{
    UIGraphicsBeginImageContextWithOptions(size, NO, 0);
    [self drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage * newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}
//这里写了一个方法传入需要的透明度和图片
- (UIImage *)imageByApplyingAlpha:(CGFloat)alpha  image:(UIImage*)image{
    UIGraphicsBeginImageContextWithOptions(image.size, NO, 0.0f);
       
       CGContextRef ctx = UIGraphicsGetCurrentContext();
       CGRect area = CGRectMake(0, 0, image.size.width, image.size.height);
       
       CGContextScaleCTM(ctx, 1, -1);
       CGContextTranslateCTM(ctx, 0, -area.size.height);
       
       CGContextSetBlendMode(ctx, kCGBlendModeMultiply);
       
       CGContextSetAlpha(ctx, alpha);
       
       CGContextDrawImage(ctx, area, image.CGImage);
       
       UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
       
       UIGraphicsEndImageContext();
       
       return newImage;
}