说起红眼算法，这个话题非常古老了。
百度百科上的描述：
“红眼”一般是指在人物摄影时，当闪光灯照射到人眼的时候，瞳孔放大而产生的视网膜泛红现象。
由于红眼现象的程度是根据拍摄对象色素的深浅决定的，如果拍摄对象的眼睛颜色较深，红眼现象便不会特别明显。
“红眼”也指传染性结膜炎。
近些年好像没有看到摄影会出现这样的情况，毕竟科技发展迅速。
记得最早看到红眼移除算法是在ACDSee 这个看图软件的编辑功能区。
当然，当时ACDSee 也没有能力做到自动去红眼，也需要进行手工操作。
红眼移除不难，其实就是把眼睛区域的颜色修正一下。
但是难就难在修复之后，不要显得太过突兀，或者破坏眼睛周围的颜色 。
这就有点难办了。
当然其实最简单的思路，就是转色域空间处理后再转回RGB。
记得在2015年的时候，
曾经一度想要寻找红眼移除过度自然的算法思路，
当时仅仅是好奇，想要学习之。
直到2016年，在一个Delphi 图像控件的源码里看到了一个红颜移除算法函数。
把代码转写成C之后验证了一下，效果不错，过度很自然。
貌似好像有点暴露年龄了，
俺也曾经是Delphi程序员来的，无比怀念Delphi7。
贴上红眼算法的Delphi源码:
procedure _IERemoveRedEyes(bitmap: TIEBitmap; fSelx1, fSely1, fSelx2, fSely2: integer; fOnProgress: TIEProgressEvent; Sender: TObject);
var
row, col: integer;
nrv, bluf, redq, powr, powb, powg: double;
per1: double;
px: PRGB;
begin
fSelX2 := imin(fSelX2, bitmap.Width); dec(fSelX2);
fSelY2 := imin(fSelY2, bitmap.Height); dec(fSelY2);
per1 := / (fSelY2 - fSelY1 + 0.5);
for row := fSelY1 to fSelY2 do
begin
px := bitmap.Scanline[row];
for col := fSelX1 to fSelX2 do
begin
nrv := px^.g + px^.b;
if nrv < then
nrv := ;
if px^.g > then
bluf := px^.b / px^.g
else
bluf := px^.b;
bluf := dMax(0.5, dMin(1.5, Sqrt(bluf)));
redq := (px^.r / nrv) * bluf;
if redq > 0.7 then
begin
powr := 1.775 - (redq * 0.75 + 0.25);
if powr < then
powr := ;
powr := powr * powr;
powb := - ( - powr) / ;
powg := - ( - powr) / ;
with px^ do
begin
r := Round(powr * r);
b := Round(powb * b);
g := Round(powg * g);
end;
end;
inc(px);
end;
if assigned(fOnProgress) then
fOnProgress(Sender, trunc(per1 * (row - fSelY1 + )));
Application.ProcessMessages;
end;
end;
非常非常简单的代码。
但是思路很巧妙。
不多说，各位看官自己品味一下。
先上个效果图:
说明下本文背景前提:
人脸识别暂时采用MTCNN，示例不考虑判断是否存在红眼。
人脸检测部分，详情见博文《MTCNN人脸检测 附完整C++代码》
算法步骤：
检测人脸，对齐得到人脸五个特征点。
算出两眼球之间的距离，
估算眼球的大概大小，
(示例代码采用 两眼球之间的距离的九分之一)
计算相应的半径，
按圆形修复眼球颜色即可。
完整示例代码献上：
#include "mtcnn.h"
#include "browse.h"
#define USE_SHELL_OPEN
#ifndef nullptr
#define nullptr 0
#endif
#if defined(_MSC_VER)
#define _CRT_SECURE_NO_WARNINGS
#include <windows.h>
#else
#include <unistd.h>
#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 <stdint.h>
#include "timing.h" char saveFile[]; unsigned char *loadImage(const char *filename, int *Width, int *Height, int *Channels) {
return stbi_load(filename, Width, Height, Channels, );
} void saveImage(const char *filename, int Width, int Height, int Channels, unsigned char *Output) {
memcpy(saveFile + strlen(saveFile), filename, strlen(filename));
*(saveFile + strlen(saveFile) + ) = ;
//保存为jpg
if (!tje_encode_to_file(saveFile, Width, Height, Channels, true, Output)) {
fprintf(stderr, "save JPEG fail.\n");
return;
} #ifdef USE_SHELL_OPEN
browse(saveFile);
#endif
} void splitpath(const char *path, char *drv, char *dir, char *name, char *ext) {
const char *end;
const char *p;
const char *s;
if (path[] && path[] == ':') {
if (drv) {
*drv++ = *path++;
*drv++ = *path++;
*drv = '\0';
}
}
else if (drv)
*drv = '\0';
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 = '\0';
}
if (dir) {
for (s = path; s < p;)
*dir++ = *s++;
*dir = '\0';
}
} 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);
size_t n = strlen(filePath);
memcpy(saveFile, filePath, n);
char *cur_saveFile = saveFile + (n - strlen(ext));
cur_saveFile[] = '_';
cur_saveFile[] = ;
} void drawPoint(unsigned char *bits, int width, int depth, int x, int y, const uint8_t *color) {
for (int i = ; i < min(depth, ); ++i) {
bits[(y * width + x) * depth + i] = color[i];
}
} void drawLine(unsigned char *bits, int width, int depth, int startX, int startY, int endX, int endY,
const uint8_t *col) {
if (endX == startX) {
if (startY > endY) {
int a = startY;
startY = endY;
endY = a;
}
for (int y = startY; y <= endY; y++) {
drawPoint(bits, width, depth, startX, y, col);
}
}
else {
float m = 1.0f * (endY - startY) / (endX - startX);
int y = ;
if (startX > endX) {
int a = startX;
startX = endX;
endX = a;
}
for (int x = startX; x <= endX; x++) {
y = (int)(m * (x - startX) + startY);
drawPoint(bits, width, depth, x, y, col);
}
}
} void drawRectangle(unsigned char *bits, int width, int depth, int x1, int y1, int x2, int y2, const uint8_t *col) {
drawLine(bits, width, depth, x1, y1, x2, y1, col);
drawLine(bits, width, depth, x2, y1, x2, y2, col);
drawLine(bits, width, depth, x2, y2, x1, y2, col);
drawLine(bits, width, depth, x1, y2, x1, y1, col);
} #ifndef MAX
#define MAX(a, b) (((a) > (b)) ? (a): (b))
#endif
#ifndef MIN
#define MIN(a, b) (((a) > (b)) ? (b): (a))
#endif unsigned char ClampToByte(int Value) {
return ((Value | ((signed int) ( - Value) >> )) & ~((signed int) Value >> ));
} int Clamp(int Value, int Min, int Max) {
if (Value < Min)
return Min;
else if (Value > Max)
return Max;
else
return Value;
} void RemoveRedEyes(unsigned char *input, unsigned char *output, int width, int height, int depth, int CenterX, int CenterY,
int Radius) {
if (depth < ) return;
if ((input == nullptr) || (output == nullptr)) return;
if ((width <= ) || (height <= )) return; int Left = Clamp(CenterX - Radius, , width);
int Top = Clamp(CenterY - Radius, , height);
int Right = Clamp(CenterX + Radius, , width);
int Bottom = Clamp(CenterY + Radius, , height);
int PowRadius = Radius * Radius; for (int Y = Top; Y < Bottom; Y++) {
unsigned char *in_scanline = input + Y * width * depth + Left * depth;
unsigned char *out_scanline = output + Y * width * depth + Left * depth;
int OffsetY = Y - CenterY;
for (int X = Left; X < Right; X++) {
int OffsetX = X - CenterX;
int dis = OffsetX * OffsetX + OffsetY * OffsetY;
if (dis <= PowRadius) {
float bluf = ;
int Red = in_scanline[];
int Green = in_scanline[];
int Blue = in_scanline[];
int nrv = Blue + Green;
if (nrv < ) nrv = ;
if (Green > )
bluf = (float) Blue / Green;
else
bluf = (float) Blue;
bluf = MAX(0.5f, MIN(1.5f, sqrt(bluf)));
float redq = (float) Red / nrv * bluf;
if (redq > 0.7f) {
float powr = 1.775f - (redq * 0.75f +
0.25f);
if (powr < ) powr = ;
powr = powr * powr;
float powb = 0.5f + powr * 0.5f;
float powg = 0.75f + powr * 0.25f;
out_scanline[] = ClampToByte(powr * Red + 0.5f);
out_scanline[] = ClampToByte(powg * Green + 0.5f);
out_scanline[] = ClampToByte(powb * Blue + 0.5f);
}
}
in_scanline += depth;
out_scanline += depth;
}
}
} int main(int argc, char **argv) {
printf("mtcnn face detection\n");
printf("blog:http://cpuimage.cnblogs.com/\n"); if (argc < ) {
printf("usage: %s model_path image_file \n ", argv[]);
printf("eg: %s ../models ../sample.jpg \n ", argv[]);
printf("press any key to exit. \n");
getchar();
return ;
}
const char *model_path = argv[];
char *szfile = argv[];
getCurrentFilePath(szfile, saveFile);
int Width = ;
int Height = ;
int Channels = ;
unsigned char *inputImage = loadImage(szfile, &Width, &Height, &Channels);
if (inputImage == nullptr || Channels != ) return -;
ncnn::Mat ncnn_img = ncnn::Mat::from_pixels(inputImage, ncnn::Mat::PIXEL_RGB, Width, Height);
std::vector<Bbox> finalBbox;
MTCNN mtcnn(model_path);
double startTime = now();
mtcnn.detect(ncnn_img, finalBbox);
double nDetectTime = calcElapsed(startTime, now());
printf("time: %d ms.\n ", (int)(nDetectTime * ));
int num_box = finalBbox.size();
printf("face num: %u \n", num_box);
bool draw_face_feat = false;
for (int i = ; i < num_box; i++) {
if (draw_face_feat) {
const uint8_t red[] = {, , }; drawRectangle(inputImage, Width, Channels, finalBbox[i].x1, finalBbox[i].y1,
finalBbox[i].x2,
finalBbox[i].y2, red);
const uint8_t blue[] = {, , }; for (int num = ; num < ; num++) {
drawPoint(inputImage, Width, Channels, (int) (finalBbox[i].ppoint[num] + 0.5f),
(int) (finalBbox[i].ppoint[num + ] + 0.5f), blue);
}
}
int left_eye_x = (int) (finalBbox[i].ppoint[] + 0.5f);
int left_eye_y = (int) (finalBbox[i].ppoint[] + 0.5f);
int right_eye_x = (int) (finalBbox[i].ppoint[] + 0.5f);
int right_eye_y = (int) (finalBbox[i].ppoint[] + 0.5f);
int dis_eye = (int) sqrtf((right_eye_x - left_eye_x) * (right_eye_x - left_eye_x) +
(right_eye_y - left_eye_y) * (right_eye_y - left_eye_y));
int radius = MAX(, dis_eye / );
RemoveRedEyes(inputImage, inputImage, Width, Height, Channels, left_eye_x, left_eye_y, radius);
RemoveRedEyes(inputImage, inputImage, Width, Height, Channels, right_eye_x, right_eye_y, radius);
}
saveImage("_done.jpg", Width, Height, Channels, inputImage);
free(inputImage);
printf("press any key to exit. \n");
getchar();
return ;
}
算法见 RemoveRedEyes ，这个技巧可以用于类似的图片颜色处理。
要看人脸检测的结果，把draw_face_feat 改为 true 即可。
项目地址:
https://github.com/cpuimage/MTCNN
参数也很简单，
mtcnn 模型文件路径 图片路径
例如: mtcnn ../models ../sample.jpg
用cmake即可进行编译示例代码，详情见CMakeLists.txt。
若有其他相关问题或者需求也可以邮件联系俺探讨。
邮箱地址是:
gaozhihan@vip.qq.com