图片保存后变大了答案

【问题标题】：Image getting bigger after saving it图片保存后变大了
【发布时间】：2015-11-11 05:30:01
【问题描述】：

如果有人能帮助我解决图像保存问题，我将不胜感激。我有一个应用程序，其中包含带有相应图像的食谱。我需要调整它们的大小以保留内存并使我的应用程序更健壮。一切看起来都很好 UIImage 有适当的尺寸。但是，当我将此图像保存到 Documents 时，它似乎变得比应有的大两倍。

我用于调整图像大小的代码：

+(UIImage *) createImageFromImage: (UIImage *)image WithName:(NSString *)name Thumbnail: (BOOL)isThumbnail{
CGSize oldSize = image.size;
CGSize newSize;
CGFloat scaleFactor;
if (isThumbnail) {
    name = [NSString stringWithFormat:@"t_%@", name];
    newSize = CGSizeMake(125, 92);
}
else{
    newSize = CGSizeMake(320, 240);
}

if (!CGSizeEqualToSize(newSize, oldSize)) {
    CGFloat widthFactor = newSize.width/oldSize.width;
    CGFloat heightFactor = newSize.height/oldSize.height;

    if (((widthFactor > heightFactor)||(heightFactor > 1))&&(widthFactor < 1)) {
        scaleFactor = widthFactor;
    }
    else{
        scaleFactor = heightFactor;
    }

    newSize.width = scaleFactor*oldSize.width;
    newSize.height = scaleFactor*oldSize.height;
}

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:name];

UIImage *newImage = nil;
newImage = [self drawImage:image InContextWithSize:newSize];
[UIImagePNGRepresentation(newImage) writeToFile:path atomically:YES];

return newImage;
}




+(UIImage *)drawImage: (UIImage *)image InContextWithSize: (CGSize) newSize {
UIImage *newImage;
UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
[image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return newImage;
}

【问题讨论】：

您希望您的新图像大小为 320、240 吗？
是的，或者任何其他尺寸我都会写在那里。但问题是最终当我打开图像时，我发现它变大了。例如，它可能变成 720*478（大两倍）。这不是我想要的

标签： ios uiimage uigraphicscontext cgsize uiimagepngrepresentation

【解决方案1】：

我刚刚更改了几行代码以获得 scaleFactor

-(UIImage *) createImageFromImage: (UIImage *)image WithName:(NSString *)name Thumbnail: (BOOL)isThumbnail{
    CGSize oldSize = image.size;
    CGSize newSize;
    CGFloat scaleFactorForWidth = 0.0,scaleFactorForHeight= 0.0;
    if (isThumbnail) {
        name = [NSString stringWithFormat:@"t_%@", name];
        newSize = CGSizeMake(125, 92);
    }
    else{
        newSize = CGSizeMake(320, 240);
    }

    if (!CGSizeEqualToSize(newSize, oldSize)) {
        CGFloat widthFactor = newSize.width/oldSize.width;
        CGFloat heightFactor = newSize.height/oldSize.height;

        if (widthFactor != 1) {
            scaleFactorForWidth = widthFactor;
             newSize.width = scaleFactorForWidth*oldSize.width;
        }

        if (heightFactor != 1) {
            scaleFactorForHeight = heightFactor;
               newSize.height = scaleFactorForHeight*oldSize.height;
        }
    }

    NSLog(@"New Size : (%f,%f)",newSize.width,newSize.height);

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:name];

    UIImage *newImage = nil;
    newImage = [self drawImage:image InContextWithSize:newSize];
    [UIImagePNGRepresentation(newImage) writeToFile:path atomically:YES];

    return newImage;
}

【讨论】：

比例因子一切正常。问题似乎与 Xcode 中 PNG 文件的标准压缩选项有关。

【解决方案2】：

问题似乎与标准 Xcode PNG 压缩选项有关。如果他不希望这种情况发生，则只需将其设置为 NO。我猜这是为了视网膜显示而制作的。

【讨论】：