我如何使用iPhone中的Objective-C来计算UIImage中的红色像素? [英] How i count red color pixel from the UIImage using objective-C in iphone?
问题描述
我是iphone软件开发的初学者。
我在皮肤癌上开发应用程序,我想要计算或计算UIImage中的红色像素,这是由iphone相机捕获的。可以从UIImage计算红色像素吗?
I m the beginner in iphone software development. I developing the application on skin cancer in which i want to calculate or count red color pixel from UIImage which is captured by iphone camera.It is possible to count red pixel from UIImage?
推荐答案
由于这是几乎每周都要问的一个问题,我决定制作一个示例项目,展示如何做到这一点。您可以在以下位置查看代码:
Since this is a question that is asked almost weekly, I decided to make a little example project that shows how to do this. You can look at the code at:
http://github.com/st3fan/iphone-experiments/tree/master/Miscellaneous/PixelAccess/
重要bit是以下代码,它接受 UIImage
,然后计算纯红色像素的数量。这是一个例子,您可以使用它并根据自己的算法进行修改:
The important bit is the following code, which takes a UIImage
and then counts the number of pure red pixels. It is an example and you can use it and modify it for your own algorithms:
/**
* Structure to keep one pixel in RRRRRRRRGGGGGGGGBBBBBBBBAAAAAAAA format
*/
struct pixel {
unsigned char r, g, b, a;
};
/**
* Process the image and return the number of pure red pixels in it.
*/
- (NSUInteger) processImage: (UIImage*) image
{
NSUInteger numberOfRedPixels = 0;
// Allocate a buffer big enough to hold all the pixels
struct pixel* pixels = (struct pixel*) calloc(1, image.size.width * image.size.height * sizeof(struct pixel));
if (pixels != nil)
{
// Create a new bitmap
CGContextRef context = CGBitmapContextCreate(
(void*) pixels,
image.size.width,
image.size.height,
8,
image.size.width * 4,
CGImageGetColorSpace(image.CGImage),
kCGImageAlphaPremultipliedLast
);
if (context != NULL)
{
// Draw the image in the bitmap
CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), image.CGImage);
// Now that we have the image drawn in our own buffer, we can loop over the pixels to
// process it. This simple case simply counts all pixels that have a pure red component.
// There are probably more efficient and interesting ways to do this. But the important
// part is that the pixels buffer can be read directly.
NSUInteger numberOfPixels = image.size.width * image.size.height;
while (numberOfPixels > 0) {
if (pixels->r == 255) {
numberOfRedPixels++;
}
pixels++;
numberOfPixels--;
}
CGContextRelease(context);
}
free(pixels);
}
return numberOfRedPixels;
}
一个关于如何调用它的简单示例:
A simple example on how to call this:
- (IBAction) processImage
{
NSUInteger numberOfRedPixels = [self processImage: [UIImage imageNamed: @"DutchFlag.png"]];
label_.text = [NSString stringWithFormat: @"There are %d red pixels in the image", numberOfRedPixels];
}
Github上的示例项目包含一个完整的工作示例。
The example project on Github contains a complete working example.
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