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POHow image pixel data "scans" the image pixels?
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  1. POHow image pixel data "scans" the image pixels?
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    copied!<p><strong>The Goal:</strong></p> <p>Finding the first black pixel on the left side of an image that contains black and transparent pixels only.</p> <p><strong>What I have:</strong></p> <p>I know how to get the pixel data and have an array of black and transparent pixels (found it here : <a href="https://stackoverflow.com/a/1262893/358480">https://stackoverflow.com/a/1262893/358480</a> ):</p> <pre><code>+ (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 &lt; count ; ++ii) { NSUInteger alpha = (rawData[byteIndex + 3] * 1.0) / 255.0; byteIndex += 4; [result addObject:[NSNumber numberWithInt:alpha]]; } free(rawData); return result; } </code></pre> <p><strong>What is the problem ?</strong></p> <p>I can not understand the order which the function "scans" the image. </p> <p>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?</p> <p>How can I get the pixels by columns?</p> <p>Thanks</p> <p>Shani</p>
 

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