如何确定图像是否是Objective-C中的逐行JPEG（隔行） [英] How to determine if an image is a progressive JPEG (interlaced) in Objective-C

问题描述

我需要在Objective-C中确定是否需要下载并显示的图像是渐进JPEG。我进行了搜索，但没有找到任何明显的方法。您能帮忙吗？

解决方案

经过更多研究，我发现了一些有关在iOS中完成操作的方法的信息。 / p>

在技术问答QA1654-使用ImageIO访问图像属性我是这样的：

  //渐进式JPEG 
 NSString * imageUrlStr = @ http://cetus.sakura.ne.jp/softlab/software/spibench/pic_22p.jpg； 
 
 CFURLRef url =（__bridge CFURLRef）[NSURL URLWithString：imageUrlStr]; 
 
 CGImageSourceRef myImageSource = CGImageSourceCreateWithURL（url，NULL）; 
 
 CFDictionaryRef imagePropertiesDictionary = CGImageSourceCopyPropertiesAtIndex（myImageSource，0，NULL）; 
  

imagePropertiesDictionary字典对于渐进式JPEG如下所示：

  imagePropertiesDictionary的打印描述字典：
 {
 ColorModel = RGB; 
深度= 8; 
 PixelHeight = 1280； 
 PixelWidth = 1024; 
 {JFIF} = {
 DensityUnit = 0; 
 IsProgressive = 1; 
 JFIFVersion =（
 1，
 0，
 1 
）; 
 XDensity = 1; 
 YDensity = 1; 
}; 
} 
  

IsProgressive = 1表示它是逐行/隔行JPEG。您可以像这样检查值：

  CFDictionaryRef JFIFDictionary =（CFDictionaryRef）CFDictionaryGetValue（imagePropertiesDictionary，kCGImagePropertyJFIFDictionary）; 
 
 CFBooleanRef isProgressive =（CFBooleanRef）CFDictionaryGetValue（JFIFDictionary，kCGImagePropertyJFIFIsProgressive）; 
 
 if（isProgressive == kCFBooleanTrue）
 NSLog（@这是一个渐进式JPEG）； 
  

I need to determine in Objective-C if an image, that needs to be downloaded and shown, is a progressive JPEG. I did some search but didn't find any obvious way. Can you help?

解决方案

After doing some more research I found some more info on the way it could be done in iOS.

Following what I read in Technical Q&A QA1654 - Accessing image properties with ImageIO I did it like this:

//Example of progressive JPEG
NSString *imageUrlStr = @"http://cetus.sakura.ne.jp/softlab/software/spibench/pic_22p.jpg";

CFURLRef url = (__bridge CFURLRef)[NSURL URLWithString:imageUrlStr];

CGImageSourceRef myImageSource = CGImageSourceCreateWithURL(url, NULL);

CFDictionaryRef imagePropertiesDictionary = CGImageSourceCopyPropertiesAtIndex(myImageSource,0, NULL);

The imagePropertiesDictionary dictionary looks like this for a progressive JPEG:

Printing description of imagePropertiesDictionary:
{
    ColorModel = RGB;
    Depth = 8;
    PixelHeight = 1280;
    PixelWidth = 1024;
    "{JFIF}" =     {
        DensityUnit = 0;
        IsProgressive = 1;
        JFIFVersion =         (
            1,
            0,
            1
        );
        XDensity = 1;
        YDensity = 1;
    };
}

IsProgressive = 1 means it's a progressive/interlaced JPEG. You can check the value like this:

CFDictionaryRef JFIFDictionary = (CFDictionaryRef)CFDictionaryGetValue(imagePropertiesDictionary, kCGImagePropertyJFIFDictionary);

CFBooleanRef isProgressive = (CFBooleanRef)CFDictionaryGetValue(JFIFDictionary, kCGImagePropertyJFIFIsProgressive);

if(isProgressive == kCFBooleanTrue)
    NSLog(@"It's a progressive JPEG");

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