图像像素数据如何“扫描”图像数据。图像像素？ [英] How image pixel data "scans" the image pixels?

问题描述

目标：

查找仅包含黑色和透明像素的图像左侧的第一个黑色像素。

Finding the first black pixel on the left side of an image that contains black and transparent pixels only.

我有什么：

我知道如何获取像素数据并拥有黑色和透明像素的数组（在此处找到： https://stackoverflow.com/a/1262893/358480 ）：

I know how to get the pixel data and have an array of black and transparent pixels (found it here : https://stackoverflow.com/a/1262893/358480 ):

+ (NSArray*)getRGBAsFromImage:(UIImage*)image atX:(int)xx andY:(int)yy count:(int)count
{
 NSMutableArray *result = [NSMutableArray arrayWithCapacity:count];

// First get the image into your data buffer
CGImageRef imageRef = [image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = malloc(height * width * 4);
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height,
                                             bitsPerComponent, bytesPerRow, colorSpace,
                                             kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);

CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);

// Now your rawData contains the image data in the RGBA8888 pixel format.
int byteIndex = (bytesPerRow * yy) + xx * bytesPerPixel;
for (int ii = 0 ; ii < count ; ++ii)
{
    NSUInteger alpha = (rawData[byteIndex + 3] * 1.0) / 255.0;
    byteIndex += 4;
    [result addObject:[NSNumber numberWithInt:alpha]];
}

free(rawData);

return result;
}

有什么问题？

我无法理解函数扫描图像的顺序。

I can not understand the order which the function "scans" the image.

我想要的只是获取图像的列并找到列表1非透明像素的第一列。这样我就会知道如何裁剪图像左侧透明的一面？

What i want is to get only the columns of the image and locate the first column that has at list 1 non-transperant pixel. this way I will know how to crop the left, transparent side of the image?

如何按列获取像素？

谢谢

Shani

推荐答案

字节从左到右，从上到下排序。所以要做你想做的事情，我想你想循环遍历 rawData ，如下所示：

The bytes are ordered left-to-right, top-to-bottom. So to do what you want, I think you want to loop over the rawData like this:

int x = 0;
int y = 0;
BOOL found = NO;
for (x = 0; x < width; x++) {
    for (y = 0; y < height; y++) {
        unsigned char alphaByte = rawData[(y*bytesPerRow)+(x*bytesPerPixel)+3];
        if (alphaByte > 0) {
            found = YES;
            break;
        }
    }
    if (found) break;
}

NSLog(@"First non-transparent pixel at %i, %i", x, y);

然后，包含非透明像素的第一列将是 x列。

Then your first column that contains a non-transparent pixel will be column x.

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