检测图像iOS中的黑色像素 [英] Detect black pixel in image iOS
问题描述
到目前为止，我搜索每个像素1通过检查颜色，看看它是否是黑色...如果不是我移动到下一个像素。这是永远的，因为我只能检查约。 100像素每秒（加速我的NSTimer冻结应用程序，因为它不能检查得足够快。）所以是有什么反正我可以只是让Xcode返回所有的像素是黑色的，忽略一切，所以我只需要检查那些像素而不是每个像素。我试图检测一个黑色像素最左边的我的图像。
这是我目前的程式码。
- （void）viewDidLoad {
timer = [NSTimer scheduledTimerWithTimeInterval：0.01
target：self
selector：@selector（onTick :)
userInfo：nil repetes：YES];
y1 = 0;
x1 = 0;
initialImage = 0;
height1 = 0;
width1 = 0;
}
- （void）onTick：（NSTimer *）timer {
if（initialImage！= 1）{
/ *
IMAGE INITIALLY GETS SET HERE ...image2.image = [blah blah blah];出于不公开原因而采取这种做法
* /
initialImage = 1;
}
// image2是我检查像素的图像。
width1 =（int）image2.size.width;
height1 =（int）image2.size.height;
CFDataRef imageData = CGDataProviderCopyData（CGImageGetDataProvider（image2.CGImage））;
const UInt32 * pixels =（const UInt32 *）CFDataGetBytePtr（imageData）;
if（（pixels [（x1 +（y1 * width1））]）== 0x000000）{// 0x000000是黑色右吗？
NSLog（@black！）;
NSLog（@x =％i，x1）;
NSLog（@y =％i，y1）;
} else {
NSLog（@val：％lu，（pixels [（x1 +（y1 * width1））]））;
NSLog（@x =％i，x1）;
NSLog（@y =％i，y1）;
x1 ++;
if（x1> = width1）{
y1 ++;
x1 = 0;
}
}
if（y1> height1）{
/ *
我的更新图像代码在此处（每次所有像素都检查
$ b * /
y1 = 0;
x1 = 0;
}
$ b b
此外，如果一个像素真的接近黑色，但不是完全黑色...我可以在某处添加一个误差的边缘，所以它仍然会检测像95％的黑色像素谢谢！
为什么不使用一个double for循环在你的函数循环所有可能的x和y？ - 坐标在图像中？当然，这将是waaaay比仅检查最多100像素每秒更快。你会想要在外循环中的x（宽度）坐标和内循环中的y（高度）坐标，使你是从左到右每次有效扫描一列像素，因为你正在尝试找到最左边的黑色像素。此外，你确定每个像素在你的图像有一个4字节（Uint32）表示？标准位图将具有每像素3个字节。要检查像素是否接近黑色，您只需单独检查像素中的每个字节，并确保它们都小于某个阈值。
编辑：因为你使用的是UIGetScreenImage，所以我假设每个像素有4个字节。
const UInt8 * pixels = CFDataGetBytePtr（imageData）;
UInt8 blackThreshold = 10; //或某个值接近0
int bytesPerPixel = 4;
for（int x = 0; x< width1; x ++）{
for（int y = 0; y< height1; y ++）{
int pixelStartIndex =（x + * width1））* bytesPerPixel;
UInt8 alphaVal = pixels [pixelStartIndex]; //可以忽略这个值
UInt8 redVal = pixels [pixelStartIndex + 1];
UInt8 greenVal = pixels [pixelStartIndex + 2];
UInt8 blueVal = pixels [pixelStartIndex + 3];
if（redVal< blackThreshold&& blueVal< blackThreshold&& greenVal< blackThreshold）{
//这个像素接近黑色...做一些事情
}
}
}
如果结果是bytesPerPixel为3，然后相应地更改该值，从for循环中删除alphaVal，并从红色，绿色和蓝色值的索引减1。
是UIGetScreenImage被认为是一个私人功能，苹果可能或不可以拒绝您使用。
As of now I am searching every pixel 1 by 1 checking the color and seeing if it's black... if it isn't I move on to the next pixel. This is taking forever as I can only check approx. 100 pixels per second (speeding up my NSTimer freezes the app because it can't check fast enough.) So is there anyway I can just have Xcode return all the pixels that are black and ignore everything else so I only have to check those pixels and not every pixel. I am trying to detect a black pixel furthest to the left on my image.
Here is my current code.
- (void)viewDidLoad {
timer = [NSTimer scheduledTimerWithTimeInterval: 0.01
target: self
selector:@selector(onTick:)
userInfo: nil repeats:YES];
y1 = 0;
x1 = 0;
initialImage = 0;
height1 = 0;
width1 = 0;
}
-(void)onTick:(NSTimer *)timer {
if (initialImage != 1) {
/*
IMAGE INITIALLY GETS SET HERE... "image2.image = [blah blah blah];" took this out for non disclosure reasons
*/
initialImage = 1;
}
//image2 is the image I'm checking the pixels of.
width1 = (int)image2.size.width;
height1 = (int)image2.size.height;
CFDataRef imageData = CGDataProviderCopyData(CGImageGetDataProvider(image2.CGImage));
const UInt32 *pixels = (const UInt32*)CFDataGetBytePtr(imageData);
if ( (pixels[(x1+(y1*width1))]) == 0x000000) { //0x000000 is black right?
NSLog(@"black!");
NSLog(@"x = %i", x1);
NSLog(@"y = %i", y1);
}else {
NSLog(@"val: %lu", (pixels[(x1+(y1*width1))]));
NSLog(@"x = %i", x1);
NSLog(@"y = %i", y1);
x1 ++;
if (x1 >= width1) {
y1 ++;
x1 = 0;
}
}
if (y1 > height1) {
/*
MY UPDATE IMAGE CODE GOES HERE (IMAGE CHANGES EVERY TIME ALL PIXELS HAVE BEEN CHECKED
*/
y1 = 0;
x1 = 0;
}
Also what if a pixel is really close to black but not perfectly black... Can I add a margin of error in there somewhere so it will still detect pixels that are like 95% black? Thanks!
Why are you using a timer at all? Why not just have a double for loop in your function that loops over all possible x- and y-coordinates in the image? Surely that would be waaaay faster than only checking at most 100 pixels per second. You would want to have the x (width) coordinates in the outer loop and the y (height) coordinates in the inner loop so that you are effectively scanning one column of pixels at a time from left to right, since you are trying to find the leftmost black pixel.
Also, are you sure that each pixel in your image has a 4-byte (Uint32) representation? A standard bitmap would have 3 bytes per pixel. To check if a pixel is close to black, you would just examine each byte in the pixel separately and make sure they are all less than some threshold.
EDIT: OK, since you are using UIGetScreenImage, I'm going to assume that it is 4-bytes per pixel.
const UInt8 *pixels = CFDataGetBytePtr(imageData);
UInt8 blackThreshold = 10; // or some value close to 0
int bytesPerPixel = 4;
for(int x = 0; x < width1; x++) {
for(int y = 0; y < height1; y++) {
int pixelStartIndex = (x + (y * width1)) * bytesPerPixel;
UInt8 alphaVal = pixels[pixelStartIndex]; // can probably ignore this value
UInt8 redVal = pixels[pixelStartIndex + 1];
UInt8 greenVal = pixels[pixelStartIndex + 2];
UInt8 blueVal = pixels[pixelStartIndex + 3];
if(redVal < blackThreshold && blueVal < blackThreshold && greenVal < blackThreshold) {
//This pixel is close to black...do something with it
}
}
}
If it turns out that bytesPerPixel is 3, then change that value accordingly, remove the alphaVal from the for loop, and subtract 1 from the indices of the red, green, and blue values.
Also, my current understanding is that UIGetScreenImage is considered a private function that Apple may or may not reject you for using.
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