我想实现一个可以识别照片文本的 OCR 应用程序。
我成功在iOS中编译和集成Tesseract引擎，在拍摄清晰的文档（或从屏幕上截取这段文字的照片）时，我成功地得到了合理的检测，但对于路标、商店标志、彩色背景等其他文本，检测失败.
问题是需要什么样的图像处理准备才能获得更好的识别。例如，我希望我们需要将图像转换为灰度/黑白以及修复对比度等。
这怎么能在 iOS 中完成，有这个包吗？
问问题
13696 次
2 回答
16
我目前正在做同样的事情。我发现保存在 Photoshop 中的 PNG 效果很好，但最初来自相机然后导入到应用程序中的图像从未工作过。不要让我解释它 - 但应用这个功能使这些图像工作。也许它也对你有用。
// this does the trick to have tesseract accept the UIImage.
UIImage * gs_convert_image (UIImage * src_img) {
CGColorSpaceRef d_colorSpace = CGColorSpaceCreateDeviceRGB();
/*
* Note we specify 4 bytes per pixel here even though we ignore the
* alpha value; you can't specify 3 bytes per-pixel.
*/
size_t d_bytesPerRow = src_img.size.width * 4;
unsigned char * imgData = (unsigned char*)malloc(src_img.size.height*d_bytesPerRow);
CGContextRef context = CGBitmapContextCreate(imgData, src_img.size.width,
src_img.size.height,
8, d_bytesPerRow,
d_colorSpace,
kCGImageAlphaNoneSkipFirst);
UIGraphicsPushContext(context);
// These next two lines 'flip' the drawing so it doesn't appear upside-down.
CGContextTranslateCTM(context, 0.0, src_img.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
// Use UIImage's drawInRect: instead of the CGContextDrawImage function, otherwise you'll have issues when the source image is in portrait orientation.
[src_img drawInRect:CGRectMake(0.0, 0.0, src_img.size.width, src_img.size.height)];
UIGraphicsPopContext();
/*
* At this point, we have the raw ARGB pixel data in the imgData buffer, so
* we can perform whatever image processing here.
*/
// After we've processed the raw data, turn it back into a UIImage instance.
CGImageRef new_img = CGBitmapContextCreateImage(context);
UIImage * convertedImage = [[UIImage alloc] initWithCGImage:
new_img];
CGImageRelease(new_img);
CGContextRelease(context);
CGColorSpaceRelease(d_colorSpace);
free(imgData);
return convertedImage;
}
我还进行了很多实验，为 tesseract 准备图像。调整大小，转换为灰度，然后调整亮度和对比度似乎效果最好。
我也试过这个 GPUImage 库。https://github.com/BradLarson/GPUImage 和 GPUImageAverageLuminanceThresholdFilter 似乎给了我一个很好的调整图像，但 tesseract 似乎不能很好地处理它。
我还将 opencv 放入我的项目中，并计划尝试它的图像例程。甚至可能进行一些框检测以找到文本区域（我希望这会加快 tesseract）。
于 2012-11-24T21:16:23.730 回答
10
我已经使用了上面的代码，但还添加了另外两个函数调用来转换图像，以便它可以与 Tesseract 一起使用。
首先，我使用图像调整大小脚本转换为 640 x 640，这对于 Tesseract 来说似乎更易于管理。
-(UIImage *)resizeImage:(UIImage *)image {
CGImageRef imageRef = [image CGImage];
CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(imageRef);
CGColorSpaceRef colorSpaceInfo = CGColorSpaceCreateDeviceRGB();
if (alphaInfo == kCGImageAlphaNone)
alphaInfo = kCGImageAlphaNoneSkipLast;
int width, height;
width = 640;//[image size].width;
height = 640;//[image size].height;
CGContextRef bitmap;
if (image.imageOrientation == UIImageOrientationUp | image.imageOrientation == UIImageOrientationDown) {
bitmap = CGBitmapContextCreate(NULL, width, height, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, alphaInfo);
} else {
bitmap = CGBitmapContextCreate(NULL, height, width, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, alphaInfo);
}
if (image.imageOrientation == UIImageOrientationLeft) {
NSLog(@"image orientation left");
CGContextRotateCTM (bitmap, radians(90));
CGContextTranslateCTM (bitmap, 0, -height);
} else if (image.imageOrientation == UIImageOrientationRight) {
NSLog(@"image orientation right");
CGContextRotateCTM (bitmap, radians(-90));
CGContextTranslateCTM (bitmap, -width, 0);
} else if (image.imageOrientation == UIImageOrientationUp) {
NSLog(@"image orientation up");
} else if (image.imageOrientation == UIImageOrientationDown) {
NSLog(@"image orientation down");
CGContextTranslateCTM (bitmap, width,height);
CGContextRotateCTM (bitmap, radians(-180.));
}
CGContextDrawImage(bitmap, CGRectMake(0, 0, width, height), imageRef);
CGImageRef ref = CGBitmapContextCreateImage(bitmap);
UIImage *result = [UIImage imageWithCGImage:ref];
CGContextRelease(bitmap);
CGImageRelease(ref);
return result;
}
为了使弧度起作用，请确保您将其声明在@implementation
static inline double radians (double degrees) {return degrees * M_PI/180;}
然后我转换为灰度。
我发现这篇文章在转换为灰度时将图像转换为灰度。
我已成功使用此处的代码，现在可以读取不同颜色的文本和不同颜色的背景
我已经稍微修改了代码以作为类中的函数而不是其他人所做的自己的类
- (UIImage *) toGrayscale:(UIImage*)img
{
const int RED = 1;
const int GREEN = 2;
const int BLUE = 3;
// Create image rectangle with current image width/height
CGRect imageRect = CGRectMake(0, 0, img.size.width * img.scale, img.size.height * img.scale);
int width = imageRect.size.width;
int height = imageRect.size.height;
// the pixels will be painted to this array
uint32_t *pixels = (uint32_t *) malloc(width * height * sizeof(uint32_t));
// clear the pixels so any transparency is preserved
memset(pixels, 0, width * height * sizeof(uint32_t));
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
// create a context with RGBA pixels
CGContextRef context = CGBitmapContextCreate(pixels, width, height, 8, width * sizeof(uint32_t), colorSpace,
kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);
// paint the bitmap to our context which will fill in the pixels array
CGContextDrawImage(context, CGRectMake(0, 0, width, height), [img CGImage]);
for(int y = 0; y < height; y++) {
for(int x = 0; x < width; x++) {
uint8_t *rgbaPixel = (uint8_t *) &pixels[y * width + x];
// convert to grayscale using recommended method: http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale
uint32_t gray = 0.3 * rgbaPixel[RED] + 0.59 * rgbaPixel[GREEN] + 0.11 * rgbaPixel[BLUE];
// set the pixels to gray
rgbaPixel[RED] = gray;
rgbaPixel[GREEN] = gray;
rgbaPixel[BLUE] = gray;
}
}
// create a new CGImageRef from our context with the modified pixels
CGImageRef image = CGBitmapContextCreateImage(context);
// we're done with the context, color space, and pixels
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
free(pixels);
// make a new UIImage to return
UIImage *resultUIImage = [UIImage imageWithCGImage:image
scale:img.scale
orientation:UIImageOrientationUp];
// we're done with image now too
CGImageRelease(image);
return resultUIImage;
}
于 2013-03-20T15:36:48.983 回答