2年前在学习图像算法的时候看到一个文档倾斜矫正的算法。
也就是说能将一些文档图像进行旋转矫正，
当然这个算法一般用于一些文档扫描软件做后处理
或者用于ocr 文字识别做前处理。
相关的关键词: 抗倾斜 反倾斜 Deskew 等等。
最简单算法实现思路，采用 霍夫变换(Hough Transform)进行直线检测，
当然也可以用霍夫变换检测圆。
在倾斜矫正算法中，自然就是检测直线。
通过对检测出来的直线进行角度判断，
一般取 认可度最高的几条直线进行计算，
最后求取均衡后的角度值。
进行图像角度的旋转即可。
大概算法步骤如下：
1.转换为灰度图
2.判断是否为文本图片，如果不是进行 进行 反相操作
3.检测直线，进行角度判断
4.通过角度进行图像旋转
这么一个基本思路，当然想要检测得更加精准，
可以做一些文本区域判断，图像修复增强之类的前处理操作。
最近有点强迫症犯了，开始回归本源，强迫自己用c语言来实现，
fastsin以及fastcos 来自 arm公司的开源项目。
霍夫变换相关算法原理，请移步 百度 google 维基百科。
或直接看代码实现，可了悟于心。
有事没事，多看看业内大公司的开源项目，
萝卜白菜都有，重点是学习其思路。
嗯，有些网友可能会说，opencv一两行代码就可以做到了。
对的，一些sdk,api,开源框架一两句代码是做到了，
知道，用到，与真正做到，这是两条路。
我只想说一句，愿世界和平。
附完整代码:
//如果是Windows的话，调用系统API ShellExecuteA打开图片 #if defined(_MSC_VER) #define _CRT_SECURE_NO_WARNINGS #include <windows.h> #define USE_SHELL_OPEN #endif #define STB_IMAGE_STATIC #define STB_IMAGE_IMPLEMENTATION #include "stb_image.h" //ref:https://github.com/nothings/stb/blob/master/stb_image.h #define TJE_IMPLEMENTATION #include "tiny_jpeg.h" //ref:https://github.com/serge-rgb/TinyJPEG/blob/master/tiny_jpeg.h #include <math.h> #include <io.h> #include <math.h> #include <stdlib.h> #include <stdbool.h> //计时 #include <stdint.h> #if defined(__APPLE__) # include <mach/mach_time.h> #elif defined(_WIN32) # define WIN32_LEAN_AND_MEAN # include <windows.h> #else // __linux # include <time.h> # ifndef CLOCK_MONOTONIC //_RAW # define CLOCK_MONOTONIC CLOCK_REALTIME # endif #endif static uint64_t nanotimer() { static int ever = 0; #if defined(__APPLE__) static mach_timebase_info_data_t frequency; if (!ever) { if (mach_timebase_info(&frequency) != KERN_SUCCESS) { return 0; } ever = 1; } return; #elif defined(_WIN32) static LARGE_INTEGER frequency; if (!ever) { QueryPerformanceFrequency(&frequency); ever = 1; } LARGE_INTEGER t; QueryPerformanceCounter(&t); return (t.QuadPart * (uint64_t)1e9) / frequency.QuadPart; #else // __linux struct timespec t; if (!ever) { if (clock_gettime(CLOCK_MONOTONIC, &spec) != 0) { return 0; } ever = 1; } clock_gettime(CLOCK_MONOTONIC, &spec); return (t.tv_sec * (uint64_t)1e9) + t.tv_nsec; #endif } static double now() { static uint64_t epoch = 0; if (!epoch) { epoch = nanotimer(); } return (nanotimer() - epoch) / 1e9; }; double calcElapsed(double start, double end) { double took = -start; return took + end; } //存储当前传入文件位置的变量 char saveFile[1024]; //加载图片 unsigned char * loadImage(const char *filename, int *Width, int *Height, int *Channels) { return stbi_load(filename, Width, Height, Channels, 0); } //保存图片 void saveImage(const char *filename, int Width, int Height, int Channels, unsigned char *Output) { memcpy(saveFile + strlen(saveFile), filename, strlen(filename)); *(saveFile + strlen(saveFile) + 1) = 0; //保存为jpg if (!tje_encode_to_file(saveFile, Width, Height, Channels, true, Output)) { fprintf(stderr, "写入 JPEG 文件失败. "); return; } #ifdef USE_SHELL_OPEN ShellExecuteA(NULL, "open", saveFile, NULL, NULL, SW_SHOW); #else //其他平台暂不实现 #endif } #ifndef ClampToByte #define ClampToByte( v ) ( ((unsigned)(int)(v)) <(255) ? (v) : ((int)(v) < 0) ? (0) : (255)) #endif #define M_PI 3.14159265358979323846f typedef struct cpu_HoughLine { float Theta; int Radius; int Intensity; float RelativeIntensity; } cpu_HoughLine; typedef struct cpu_rect { int x; int y; int Width; int Height; } cpu_rect; #ifndef clamp #define clamp(value,min,max) ((value) > (max )? (max ): (value) < (min) ? (min) : (value)) #endif #define FAST_MATH_TABLE_SIZE 512 const float sinTable_f32[FAST_MATH_TABLE_SIZE + 1] = { 0.00000000f, 0.01227154f, 0.02454123f, 0.03680722f, 0.04906767f, 0.06132074f, 0.07356456f, 0.08579731f, 0.09801714f, 0.11022221f, 0.12241068f, 0.13458071f, 0.14673047f, 0.15885814f, 0.17096189f, 0.18303989f, 0.19509032f, 0.20711138f, 0.21910124f, 0.23105811f, 0.24298018f, 0.25486566f, 0.26671276f, 0.27851969f, 0.29028468f, 0.30200595f, 0.31368174f, 0.32531029f, 0.33688985f, 0.34841868f, 0.35989504f, 0.37131719f, 0.38268343f, 0.39399204f, 0.40524131f, 0.41642956f, 0.42755509f, 0.43861624f, 0.44961133f, 0.46053871f, 0.47139674f, 0.48218377f, 0.49289819f, 0.50353838f, 0.51410274f, 0.52458968f, 0.53499762f, 0.54532499f, 0.55557023f, 0.56573181f, 0.57580819f, 0.58579786f, 0.59569930f, 0.60551104f, 0.61523159f, 0.62485949f, 0.63439328f, 0.64383154f, 0.65317284f, 0.66241578f, 0.67155895f, 0.68060100f, 0.68954054f, 0.69837625f, 0.70710678f, 0.71573083f, 0.72424708f, 0.73265427f, 0.74095113f, 0.74913639f, 0.75720885f, 0.76516727f, 0.77301045f, 0.78073723f, 0.78834643f, 0.79583690f, 0.80320753f, 0.81045720f, 0.81758481f, 0.82458930f, 0.83146961f, 0.83822471f, 0.84485357f, 0.85135519f, 0.85772861f, 0.86397286f, 0.87008699f, 0.87607009f, 0.88192126f, 0.88763962f, 0.89322430f, 0.89867447f, 0.90398929f, 0.90916798f, 0.91420976f, 0.91911385f, 0.92387953f, 0.92850608f, 0.93299280f, 0.93733901f, 0.94154407f, 0.94560733f, 0.94952818f, 0.95330604f, 0.95694034f, 0.96043052f, 0.96377607f, 0.96697647f, 0.97003125f, 0.97293995f, 0.97570213f, 0.97831737f, 0.98078528f, 0.98310549f, 0.98527764f, 0.98730142f, 0.98917651f, 0.99090264f, 0.99247953f, 0.99390697f, 0.99518473f, 0.99631261f, 0.99729046f, 0.99811811f, 0.99879546f, 0.99932238f, 0.99969882f, 0.99992470f, 1.00000000f, 0.99992470f, 0.99969882f, 0.99932238f, 0.99879546f, 0.99811811f, 0.99729046f, 0.99631261f, 0.99518473f, 0.99390697f, 0.99247953f, 0.99090264f, 0.98917651f, 0.98730142f, 0.98527764f, 0.98310549f, 0.98078528f, 0.97831737f, 0.97570213f, 0.97293995f, 0.97003125f, 0.96697647f, 0.96377607f, 0.96043052f, 0.95694034f, 0.95330604f, 0.94952818f, 0.94560733f, 0.94154407f, 0.93733901f, 0.93299280f, 0.92850608f, 0.92387953f, 0.91911385f, 0.91420976f, 0.90916798f, 0.90398929f, 0.89867447f, 0.89322430f, 0.88763962f, 0.88192126f, 0.87607009f, 0.87008699f, 0.86397286f, 0.85772861f, 0.85135519f, 0.84485357f, 0.83822471f, 0.83146961f, 0.82458930f, 0.81758481f, 0.81045720f, 0.80320753f, 0.79583690f, 0.78834643f, 0.78073723f, 0.77301045f, 0.76516727f, 0.75720885f, 0.74913639f, 0.74095113f, 0.73265427f, 0.72424708f, 0.71573083f, 0.70710678f, 0.69837625f, 0.68954054f, 0.68060100f, 0.67155895f, 0.66241578f, 0.65317284f, 0.64383154f, 0.63439328f, 0.62485949f, 0.61523159f, 0.60551104f, 0.59569930f, 0.58579786f, 0.57580819f, 0.56573181f, 0.55557023f, 0.54532499f, 0.53499762f, 0.52458968f, 0.51410274f, 0.50353838f, 0.49289819f, 0.48218377f, 0.47139674f, 0.46053871f, 0.44961133f, 0.43861624f, 0.42755509f, 0.41642956f, 0.40524131f, 0.39399204f, 0.38268343f, 0.37131719f, 0.35989504f, 0.34841868f, 0.33688985f, 0.32531029f, 0.31368174f, 0.30200595f, 0.29028468f, 0.27851969f, 0.26671276f, 0.25486566f, 0.24298018f, 0.23105811f, 0.21910124f, 0.20711138f, 0.19509032f, 0.18303989f, 0.17096189f, 0.15885814f, 0.14673047f, 0.13458071f, 0.12241068f, 0.11022221f, 0.09801714f, 0.08579731f, 0.07356456f, 0.06132074f, 0.04906767f, 0.03680722f, 0.02454123f, 0.01227154f, 0.00000000f, -0.01227154f, -0.02454123f, -0.03680722f, -0.04906767f, -0.06132074f, -0.07356456f, -0.08579731f, -0.09801714f, -0.11022221f, -0.12241068f, -0.13458071f, -0.14673047f, -0.15885814f, -0.17096189f, -0.18303989f, -0.19509032f, -0.20711138f, -0.21910124f, -0.23105811f, -0.24298018f, -0.25486566f, -0.26671276f, -0.27851969f, -0.29028468f, -0.30200595f, -0.31368174f, -0.32531029f, -0.33688985f, -0.34841868f, -0.35989504f, -0.37131719f, -0.38268343f, -0.39399204f, -0.40524131f, -0.41642956f, -0.42755509f, -0.43861624f, -0.44961133f, -0.46053871f, -0.47139674f, -0.48218377f, -0.49289819f, -0.50353838f, -0.51410274f, -0.52458968f, -0.53499762f, -0.54532499f, -0.55557023f, -0.56573181f, -0.57580819f, -0.58579786f, -0.59569930f, -0.60551104f, -0.61523159f, -0.62485949f, -0.63439328f, -0.64383154f, -0.65317284f, -0.66241578f, -0.67155895f, -0.68060100f, -0.68954054f, -0.69837625f, -0.70710678f, -0.71573083f, -0.72424708f, -0.73265427f, -0.74095113f, -0.74913639f, -0.75720885f, -0.76516727f, -0.77301045f, -0.78073723f, -0.78834643f, -0.79583690f, -0.80320753f, -0.81045720f, -0.81758481f, -0.82458930f, -0.83146961f, -0.83822471f, -0.84485357f, -0.85135519f, -0.85772861f, -0.86397286f, -0.87008699f, -0.87607009f, -0.88192126f, -0.88763962f, -0.89322430f, -0.89867447f, -0.90398929f, -0.90916798f, -0.91420976f, -0.91911385f, -0.92387953f, -0.92850608f, -0.93299280f, -0.93733901f, -0.94154407f, -0.94560733f, -0.94952818f, -0.95330604f, -0.95694034f, -0.96043052f, -0.96377607f, -0.96697647f, -0.97003125f, -0.97293995f, -0.97570213f, -0.97831737f, -0.98078528f, -0.98310549f, -0.98527764f, -0.98730142f, -0.98917651f, -0.99090264f, -0.99247953f, -0.99390697f, -0.99518473f, -0.99631261f, -0.99729046f, -0.99811811f, -0.99879546f, -0.99932238f, -0.99969882f, -0.99992470f, -1.00000000f, -0.99992470f, -0.99969882f, -0.99932238f, -0.99879546f, -0.99811811f, -0.99729046f, -0.99631261f, -0.99518473f, -0.99390697f, -0.99247953f, -0.99090264f, -0.98917651f, -0.98730142f, -0.98527764f, -0.98310549f, -0.98078528f, -0.97831737f, -0.97570213f, -0.97293995f, -0.97003125f, -0.96697647f, -0.96377607f, -0.96043052f, -0.95694034f, -0.95330604f, -0.94952818f, -0.94560733f, -0.94154407f, -0.93733901f, -0.93299280f, -0.92850608f, -0.92387953f, -0.91911385f, -0.91420976f, -0.90916798f, -0.90398929f, -0.89867447f, -0.89322430f, -0.88763962f, -0.88192126f, -0.87607009f, -0.87008699f, -0.86397286f, -0.85772861f, -0.85135519f, -0.84485357f, -0.83822471f, -0.83146961f, -0.82458930f, -0.81758481f, -0.81045720f, -0.80320753f, -0.79583690f, -0.78834643f, -0.78073723f, -0.77301045f, -0.76516727f, -0.75720885f, -0.74913639f, -0.74095113f, -0.73265427f, -0.72424708f, -0.71573083f, -0.70710678f, -0.69837625f, -0.68954054f, -0.68060100f, -0.67155895f, -0.66241578f, -0.65317284f, -0.64383154f, -0.63439328f, -0.62485949f, -0.61523159f, -0.60551104f, -0.59569930f, -0.58579786f, -0.57580819f, -0.56573181f, -0.55557023f, -0.54532499f, -0.53499762f, -0.52458968f, -0.51410274f, -0.50353838f, -0.49289819f, -0.48218377f, -0.47139674f, -0.46053871f, -0.44961133f, -0.43861624f, -0.42755509f, -0.41642956f, -0.40524131f, -0.39399204f, -0.38268343f, -0.37131719f, -0.35989504f, -0.34841868f, -0.33688985f, -0.32531029f, -0.31368174f, -0.30200595f, -0.29028468f, -0.27851969f, -0.26671276f, -0.25486566f, -0.24298018f, -0.23105811f, -0.21910124f, -0.20711138f, -0.19509032f, -0.18303989f, -0.17096189f, -0.15885814f, -0.14673047f, -0.13458071f, -0.12241068f, -0.11022221f, -0.09801714f, -0.08579731f, -0.07356456f, -0.06132074f, -0.04906767f, -0.03680722f, -0.02454123f, -0.01227154f, -0.00000000f }; inline float fastSin( float x) { float sinVal, fract, in; unsigned short index; float a, b; int n; float findex; in = x * 0.159154943092f; n = (int)in; if (x < 0.0f) { n--; } in = in - (float)n; findex = (float)FAST_MATH_TABLE_SIZE * in; if (findex >= 512.0f) { findex -= 512.0f; } index = ((unsigned short)findex) & 0x1ff; fract = findex - (float)index; a = sinTable_f32[index]; b = sinTable_f32[index + 1]; sinVal = (1.0f - fract)*a + fract*b; return (sinVal); } inline float fastCos( float x) { float cosVal, fract, in; unsigned short index; float a, b; int n; float findex; in = x * 0.159154943092f + 0.25f; n = (int)in; if (in < 0.0f) { n--; } in = in - (float)n; findex = (float)FAST_MATH_TABLE_SIZE * in; index = ((unsigned short)findex) & 0x1ff; fract = findex - (float)index; a = sinTable_f32[index]; b = sinTable_f32[index + 1]; cosVal = (1.0f - fract)*a + fract*b; return (cosVal); } void CPUImageGrayscaleFilter(unsigned char* Input, unsigned char* Output, int Width, int Height, int Stride) { int Channels = Stride / Width; const int B_WT = (int)(0.114 * 256 + 0.5); const int G_WT = (int)(0.587 * 256 + 0.5); const int R_WT = 256 - B_WT - G_WT; // int(0.299 * 256 + 0.5); int Channel = Stride / Width; if (Channel == 3) { for (int Y = 0; Y < Height; Y++) { unsigned char *LinePS = Input + Y * Stride; unsigned char *LinePD = Output + Y * Width; int X = 0; for (; X < Width - 4; X += 4, LinePS += Channel * 4) { LinePD[X + 0] = (B_WT * LinePS[0] + G_WT * LinePS[1] + R_WT * LinePS[2]) >> 8; LinePD[X + 1] = (B_WT * LinePS[3] + G_WT * LinePS[4] + R_WT * LinePS[5]) >> 8; LinePD[X + 2] = (B_WT * LinePS[6] + G_WT * LinePS[7] + R_WT * LinePS[8]) >> 8; LinePD[X + 3] = (B_WT * LinePS[9] + G_WT * LinePS[10] + R_WT * LinePS[11]) >> 8; } for (; X < Width; X++, LinePS += Channel) { LinePD[X] = (B_WT * LinePS[0] + G_WT * LinePS[1] + R_WT * LinePS[2]) >> 8; } } } else if (Channel == 4) { for (int Y = 0; Y < Height; Y++) { unsigned char *LinePS = Input + Y * Stride; unsigned char *LinePD = Output + Y * Width; int X = 0; for (; X < Width - 4; X += 4, LinePS += Channel * 4) { LinePD[X + 0] = (B_WT * LinePS[0] + G_WT * LinePS[1] + R_WT * LinePS[2]) >> 8; LinePD[X + 1] = (B_WT * LinePS[4] + G_WT * LinePS[5] + R_WT * LinePS[6]) >> 8; LinePD[X + 2] = (B_WT * LinePS[8] + G_WT * LinePS[9] + R_WT * LinePS[10]) >> 8; LinePD[X + 3] = (B_WT * LinePS[12] + G_WT * LinePS[13] + R_WT * LinePS[14]) >> 8; } for (; X < Width; X++, LinePS += Channel) { LinePD[X] = (B_WT * LinePS[0] + G_WT * LinePS[1] + R_WT * LinePS[2]) >> 8; } } } else if (Channel == 1) { if (Output != Input) { memcpy(Output, Input, Height*Stride); } } } void CPUImageColorInvertFilter(unsigned char* Input, unsigned char* Output, int Width, int Height, int Stride) { int Channels = Stride / Width; unsigned char invertMap[256] = { 0 }; for (int pixel = 0; pixel < 256; pixel++) { invertMap[pixel] = (255 - pixel); } if (Channels == 1) { for (int Y = 0; Y < Height; Y++) { unsigned char* pOutput = Output + (Y * Stride); unsigned char* pInput = Input + (Y * Stride); for (int X = 0; X < Width; X++) { pOutput[X] = invertMap[pInput[X]]; } } } else { for (int Y = 0; Y < Height; Y++) { unsigned char* pOutput = Output + (Y * Stride); unsigned char* pInput = Input + (Y * Stride); for (int X = 0; X < Width; X++) { pOutput[0] = invertMap[pInput[0]]; pOutput[1] = invertMap[pInput[1]]; pOutput[2] = invertMap[pInput[2]]; pInput += Channels; pOutput += Channels; } } } } float CPUImageCalcSkewAngle(unsigned char* Input, int Width, int Height, cpu_rect *CheckRectPtr, int maxSkewToDetect, int stepsPerDegree, int localPeakRadius, int nLineCount) { cpu_rect CheckRect = *CheckRectPtr; //确定指定的区域在原图片范围内 CheckRect.x = clamp(CheckRect.x, 0, Width - 1); CheckRect.y = clamp(CheckRect.y, 0, Height - 1); CheckRect.Width = clamp(CheckRect.Width, 1, Width - 1); CheckRect.Height = clamp(CheckRect.Height, 1, Height - 1); // 处理参数 maxSkewToDetect = clamp(maxSkewToDetect, 0, 91); localPeakRadius = clamp(localPeakRadius, 1, 10); stepsPerDegree = clamp(stepsPerDegree, 1, 10); int houghHeight = (2 * maxSkewToDetect * stepsPerDegree); float thetaStep = (2 * maxSkewToDetect * M_PI / 180) / houghHeight; int halfWidth = Width >> 1; int halfHeight = Height >> 1; // 计算 Hough 映射宽度 int halfHoughWidth = (int)sqrtf((float)(halfWidth * halfWidth + halfHeight * halfHeight)); int houghWidth = (halfHoughWidth * 2); float minTheta = 90.0f - maxSkewToDetect; unsigned short * houghMap = (unsigned short *)calloc(houghHeight*houghWidth, sizeof(unsigned short)); float* sinMap = (float*)malloc(houghHeight * sizeof(float)); float* cosMap = (float*)malloc(houghHeight * sizeof(float)); cpu_HoughLine* HoughLines = (cpu_HoughLine*)calloc(houghHeight*houghWidth, sizeof(cpu_HoughLine)); if (houghMap == NULL || sinMap == NULL || cosMap == NULL || HoughLines == NULL) { if (houghMap) { free(houghMap); houghMap = NULL; } if (sinMap) { free(sinMap); sinMap = NULL; } if (cosMap) { free(cosMap); cosMap = NULL; } if (HoughLines) { free(HoughLines); HoughLines = NULL; } return 0.0f; } else { // 预计算 Sin 与 Cos表 float mt = (minTheta * M_PI / 180.0f); for (int i = 0; i < houghHeight; i++) { float cur_weight = mt + (i * thetaStep); sinMap[i] = fastSin(cur_weight); cosMap[i] = fastCos(cur_weight); } } int startX = -halfWidth + CheckRect.x; int startY = -halfHeight + CheckRect.y; int stopX = Width - halfWidth - (Width - CheckRect.Width); int stopY = Height - halfHeight - (Height - CheckRect.Height) - 1; int offset = Width - CheckRect.Width; unsigned char* src = Input + CheckRect.y * Width + CheckRect.x; unsigned char* srcBelow = src + Width; for (int Y = startY; Y < stopY; Y++) { for (int X = startX; X < stopX; X++, src++, srcBelow++) { if ((*src < 128) && (*srcBelow >= 128)) { for (int theta = 0; theta < houghHeight; theta++) { int radius = (int)(cosMap[theta] * X - sinMap[theta] * Y) + halfHoughWidth; if ((radius < 0) || (radius >= houghWidth)) { continue; } houghMap[theta*houghWidth + radius]++; } } } src += offset; srcBelow += offset; } // 找到 Hough映射的最大值 float maxMapIntensity = 0.0000000001f; for (int theta = 0; theta < houghHeight; theta++) { unsigned short * houghMapLine = houghMap + theta*houghWidth; for (int radius = 0; radius < houghWidth; radius++) { maxMapIntensity = max(maxMapIntensity, houghMapLine[radius]); } } int minLineIntensity = Width / 10; // 收集大于或等于指定强度的直线 int lineIntensity = 0; bool foundGreater = false; int lineSize = 0; for (int theta = 0; theta < houghHeight; theta++) { unsigned short * houghMapLine = houghMap + theta*houghWidth; for (int radius = 0; radius < houghWidth; radius++) { // 取当前强度 lineIntensity = houghMapLine[radius]; if (lineIntensity < minLineIntensity) { continue; } foundGreater = false; // 检查邻边 for (int t = theta - localPeakRadius, ttMax = theta + localPeakRadius; t < ttMax; t++) { //跳过map值 if (t < 0) { continue; } if (t >= houghHeight) { break; } //如果不是局部最大则跳出 if (foundGreater == true) { break; } for (int r = radius - localPeakRadius, trMax = radius + localPeakRadius; r < trMax; r++) { //跳过map值 if (r < 0) { continue; } if (r >= houghWidth) { break; } // 当前值与邻边对比 if (houghMap[t*houghWidth + r] > lineIntensity) { foundGreater = true; break; } } } // 可能是局部最大值,记录下来 if (!foundGreater) { cpu_HoughLine tempVar; tempVar.Theta = 90.0f - maxSkewToDetect + (theta) / stepsPerDegree; tempVar.Radius = (radius - halfHoughWidth); tempVar.Intensity = lineIntensity; tempVar.RelativeIntensity = lineIntensity / maxMapIntensity; HoughLines[lineSize] = tempVar; lineSize++; } } } float skewAngle = 0; if (lineSize > 0) { //排序，从大到小 cpu_HoughLine temp; for (int i = 0; i < lineSize; i++) { for (int j = 0; j < lineSize - 1; j++) { if (HoughLines[j].Intensity < HoughLines[j + 1].Intensity) { temp = HoughLines[j + 1]; HoughLines[j + 1] = HoughLines[j]; HoughLines[j] = temp; } } } int n = min(nLineCount, lineSize); float sumIntensity = 0; for (int i = 0; i < n; i++) { if (HoughLines[i].RelativeIntensity > 0.5f) { skewAngle += (HoughLines[i].Theta * HoughLines[i].RelativeIntensity); sumIntensity += HoughLines[i].RelativeIntensity; } } skewAngle = skewAngle / sumIntensity; } if (houghMap) { free(houghMap); houghMap = NULL; } if (sinMap) { free(sinMap); sinMap = NULL; } if (cosMap) { free(cosMap); cosMap = NULL; } if (HoughLines) { free(HoughLines); HoughLines = NULL; } if (skewAngle != 0) { return skewAngle - 90.0f; } return skewAngle; } void CPUImageRotateBilinear(unsigned char * Input, int Width, int Height, int Stride, unsigned char * Output, int outWidth, int outHeight, float angle, bool keepSize, int fillColorR, int fillColorG, int fillColorB) { if (Input == NULL || Output == NULL) return; float oldXradius = (float)(Width - 1) / 2; float oldYradius = (float)(Height - 1) / 2; // 输出图像的半径大小 float newXradius = (float)(outWidth - 1) / 2; float newYradius = (float)(outHeight - 1) / 2; // 角度的正弦和余弦 float angleRad = -angle * M_PI / 180.0f; float angleCos = fastCos(angleRad); float angleSin = fastSin(angleRad); int Channels = Stride / Width; int dstOffset = outWidth*Channels - ((Channels == 1) ? outWidth : outWidth * Channels); // 背景色 unsigned char fillR = fillColorR; unsigned char fillG = fillColorG; unsigned char fillB = fillColorB; // 临界点 int lastHeight = Height - 1; int lastWidth = Width - 1; // 四点指针 unsigned char* src = (unsigned char*)Input; unsigned char* dst = (unsigned char*)Output; // cx, cy 目标像素的相对于图像中心的坐标 if (Channels == 1) { float cy = -newYradius; for (int y = 0; y < outHeight; y++) { const float tx = angleSin * cy + oldXradius; const float ty = angleCos * cy + oldYradius; float cx = -newXradius; for (int x = 0; x < outWidth; x++, dst++) { // 初始起点位置 const float ox = tx + angleCos * cx; const float oy = ty - angleSin * cx; const int ox1 = (int)ox; const int oy1 = (int)oy; // 判断是否为有效区域 if ((ox1 < 0) || (oy1 < 0) || (ox1 >= Width) || (oy1 >= Height)) { // 无效区域填充背景 *dst = fillG; } else { // 边界点处理 const int ox2 = (ox1 == lastWidth) ? ox1 : ox1 + 1; const int oy2 = (oy1 == lastHeight) ? oy1 : oy1 + 1; float dx1 = ox - (float)ox1; if (dx1 < 0) dx1 = 0; const float dx2 = 1.0f - dx1; float dy1 = oy - (float)oy1; if (dy1 < 0) dy1 = 0; const float dy2 = 1.0f - dy1; unsigned char*p1 = src + oy1 * Stride; unsigned char* p2 = src + oy2 * Stride; // 进行四点插值 *dst = (unsigned char)( dy2 * (dx2 * p1[ox1] + dx1 * p1[ox2]) + dy1 * (dx2 * p2[ox1] + dx1 * p2[ox2])); } cx++; } cy++; dst += dstOffset; } } else { float cy = -newYradius; for (int y = 0; y < outHeight; y++) { const float tx = angleSin * cy + oldXradius; const float ty = angleCos * cy + oldYradius; float cx = -newXradius; for (int x = 0; x < outWidth; x++, dst += Channels) { // 初始起点位置 const float ox = tx + angleCos * cx; const float oy = ty - angleSin * cx; const int ox1 = (int)ox; const int oy1 = (int)oy; // 判断是否为有效区域 if ((ox1 < 0) || (oy1 < 0) || (ox1 >= Width) || (oy1 >= Height)) { // 无效区域填充背景 dst[0] = fillR; dst[1] = fillG; dst[2] = fillB; } else { // 边界点处理 const int ox2 = (ox1 == lastWidth) ? ox1 : ox1 + 1; const int oy2 = (oy1 == lastHeight) ? oy1 : oy1 + 1; float dx1 = ox - (float)ox1; if (dx1 < 0) dx1 = 0; const float dx2 = 1.0f - dx1; float dy1 = oy - (float)oy1; if (dy1 < 0) dy1 = 0; const float dy2 = 1.0f - dy1; // 计算四点的坐标 unsigned char* p1 = src + oy1 * Stride; unsigned char* p2 = p1; p1 += ox1 * Channels; p2 += ox2 * Channels; unsigned char* p3 = src + oy2 * Stride; unsigned char* p4 = p3; p3 += ox1 * Channels; p4 += ox2 * Channels; // 进行四点插值 dst[0] = (unsigned char)( dy2 * (dx2 * p1[0] + dx1 * p2[0]) + dy1 * (dx2 * p3[0] + dx1 * p4[0])); dst[1] = (unsigned char)( dy2 * (dx2 * p1[1] + dx1 * p2[1]) + dy1 * (dx2 * p3[1] + dx1 * p4[1])); dst[2] = (unsigned char)( dy2 * (dx2 * p1[2] + dx1 * p2[2]) + dy1 * (dx2 * p3[2] + dx1 * p4[2])); } cx++; } cy++; dst += dstOffset; } } } bool CPUImageIsTextImage(unsigned char * Input, int Width, int Height) { const int blacklimit = 20; const int greylimit = 140; const int contrast_offset = 80; int prev_color[256]; int cur_color[256]; for (int i = 0; i < 256; i++) { cur_color[i] = 0; prev_color[i] = 0; } for (int i = 0; i <= blacklimit; i++) { //黑色 cur_color[i] = 100; prev_color[i] = 100000; } for (int i = blacklimit + 1 + contrast_offset; i <= greylimit; i++) { //灰色 cur_color[i] = 10; prev_color[i] = 10000; } for (int i = greylimit + 1 + contrast_offset; i <= 255; i++) { //白色 cur_color[i] = 1; prev_color[i] = 1000; } int line_count = 0; int n = -1; for (int y = 0; y < Height; y += 10) { n++; int white_amt = 0; unsigned char * buffer = Input + y*Width; int x = 0; for (x = 1; x < Width; x++) { const unsigned char prev_pixel = buffer[(x - 1)]; const unsigned char cur_pixel = buffer[x]; if ((prev_color[prev_pixel]) && (cur_color[cur_pixel])) { //是否是白色 if ((prev_color[prev_pixel] + cur_color[cur_pixel]) == 1001) { white_amt++; } } } //白色的一行 if (((float)white_amt / (float)x) > 0.85f) { line_count++; } } float line_count_ratio = (n != 0.f) ? (float)line_count / (float)n : 0.0f; if (line_count_ratio < 0.4f || line_count_ratio > 1.0f) { return false; } return true; } bool CPUImageDocumentDeskew(unsigned char * Input, unsigned char *Output, int Width, int Height, int Stride) { if (Input == NULL || Output == NULL || Input == Output) return false; int Channels = Stride / Width; //最大倾斜角度 int maxSkewToDetect = 89; cpu_rect rect = { 0 }; rect.Width = Width; rect.Height = Height; // 以最大权重的2条直线为基准计算倾斜角度 int nLineCount = 2; //角度步进数 int stepsPerDegree = 1; //局部临界半径 int localPeakRadius = 10; CPUImageGrayscaleFilter(Input, Output, Width, Height, Stride); if (!CPUImageIsTextImage(Output, Width, Height)) { CPUImageColorInvertFilter(Output, Output, Width, Height, Width); } float skewAngle = CPUImageCalcSkewAngle(Output, Width, Height, &rect, maxSkewToDetect, stepsPerDegree, localPeakRadius, nLineCount); if ((skewAngle == 0) || (skewAngle < -maxSkewToDetect || skewAngle > maxSkewToDetect)) { memcpy(Output, Input, Height* Stride * sizeof(unsigned char)); return false; } else { CPUImageRotateBilinear(Input, Width, Height, Stride, Output, Width, Height, -skewAngle, true, 255, 255, 255); } return true; } //分割路径函数 void splitpath(const char* path, char* drv, char* dir, char* name, char* ext) { const char* end; const char* p; const char* s; if (path[0] && path[1] == ':') { if (drv) { *drv++ = *path++; *drv++ = *path++; *drv = ' '; } } else if (drv) *drv = ' '; for (end = path; *end && *end != ':';) end++; for (p = end; p > path && *--p != '\' && *p != '/';) if (*p == '.') { end = p; break; } if (ext) for (s = end; (*ext = *s++);) ext++; for (p = end; p > path;) if (*--p == '\' || *p == '/') { p++; break; } if (name) { for (s = p; s < end;) *name++ = *s++; *name = ' '; } if (dir) { for (s = path; s < p;) *dir++ = *s++; *dir = ' '; } } //取当前传入的文件位置 void getCurrentFilePath(const char *filePath, char *saveFile) { char drive[_MAX_DRIVE]; char dir[_MAX_DIR]; char fname[_MAX_FNAME]; char ext[_MAX_EXT]; splitpath(filePath, drive, dir, fname, ext); int n = strlen(filePath); memcpy(saveFile, filePath, n); char * cur_saveFile = saveFile + (n - strlen(ext)); cur_saveFile[0] = '_'; cur_saveFile[1] = 0; } int main(int argc, char **argv) { printf("Image Processing "); printf("博客:http://cpuimage.cnblogs.com/ "); printf("支持解析如下图片格式: "); printf("JPG, PNG, TGA, BMP, PSD, GIF, HDR, PIC "); //检查参数是否正确 if (argc < 2) { printf("参数错误。 "); printf("请拖放文件到可执行文件上，或使用命令行：imageProc.exe 图片 "); printf("请拖放文件例如: imageProc.exe d:\image.jpg "); return 0; } char*szfile = argv[1]; //检查输入的文件是否存在 if (_access(szfile, 0) == -1) { printf("输入的文件不存在，参数错误！ "); } getCurrentFilePath(szfile, saveFile); int Width = 0; //图片宽度 int Height = 0; //图片高度 int Channels = 0; //图片通道数 unsigned char *inputImage = NULL; //输入图片指针 double startTime = now(); //加载图片 inputImage = loadImage(szfile, &Width, &Height, &Channels); double nLoadTime = calcElapsed(startTime, now()); printf("加载耗时: %d 毫秒! ", (int)(nLoadTime * 1000)); if ((Channels != 0) && (Width != 0) && (Height != 0)) { //分配与载入同等内存用于处理后输出结果 unsigned char *outputImg = (unsigned char *)stbi__malloc(Width * Channels * Height * sizeof(unsigned char)); if (inputImage) { //如果图片加载成功，则将内容复制给输出内存，方便处理 memcpy(outputImg, inputImage, Width * Channels * Height); } else { printf("加载文件: %s 失败! ", szfile); } startTime = now(); //处理算法 CPUImageDocumentDeskew(inputImage, outputImg, Width, Height, Width*Channels); double nProcessTime = calcElapsed(startTime, now()); printf("处理耗时: %d 毫秒! ", (int)(nProcessTime * 1000)); //保存处理后的图片 startTime = now(); saveImage("_done.jpg", Width, Height, Channels, outputImg); double nSaveTime = calcElapsed(startTime, now()); printf("保存耗时: %d 毫秒! ", (int)(nSaveTime * 1000)); //释放占用的内存 if (outputImg) { stbi_image_free(outputImg); outputImg = NULL; } if (inputImage) { stbi_image_free(inputImage); inputImage = NULL; } } else { printf("加载文件: %s 失败! ", szfile); } getchar(); printf("按任意键退出程序 "); return EXIT_SUCCESS; }
项目地址:https://github.com/cpuimage/deskew
贴上几张效果图.
以上，权当抛砖引玉。
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