The following code runs without exception on iOS (Xcode-v6.2 and openCV-v3.0beta). But for some reason the image the function returns is "black" !
The code is adapted from this link ! I tried to replace the oldish "IplImage*" by more modern "cv::Mat" matrices. Does anybody know if my function still has a mistake or why it would return a completely "black" image instead of a colored image in HSV-format.
By the way, the reason I would want to use this function [instead of cvtColor(cv_src, imgHSV, cv::COLOR_BGR2HSV)] is that I would like to get 0-255 range of Hue-values's (...since OpenCV only allows Hues up to 180 instead of 255).
// Create a HSV image from the RGB image using the full 8-bits, since OpenCV only allows Hues up to 180 instead of 255.
cv::Mat convertImageRGBtoHSV(cv::Mat imageRGB) {
float fR, fG, fB;
float fH, fS, fV;
const float FLOAT_TO_BYTE = 255.0f;
const float BYTE_TO_FLOAT = 1.0f / FLOAT_TO_BYTE;
// Create a blank HSV image
cv::Mat imageHSV(imageRGB.rows, imageRGB.cols, CV_8UC3);
int rowSizeHSV = (int)imageHSV.step; // Size of row in bytes, including extra padding.
char *imHSV = (char*)imageHSV.data; // Pointer to the start of the image pixels.
if (imageRGB.depth() == 8 && imageRGB.channels() == 3) {
std::vector<cv::Mat> planes(3);
cv::split(imageRGB, planes);
cv::Mat R = planes[2];
cv::Mat G = planes[1];
cv::Mat B = planes[0];
for(int y = 0; y < imageRGB.rows; ++y)
{
// get pointers to each row
cv::Vec3b* row = imageRGB.ptr<cv::Vec3b>(y);
// now scan the row
for(int x = 0; x < imageRGB.cols; ++x)
{
// Get the RGB pixel components. NOTE that OpenCV stores RGB pixels in B,G,R order.
cv::Vec3b pixel = row[x];
int bR = pixel[2];
int bG = pixel[1];
int bB = pixel[0];
// Convert from 8-bit integers to floats.
fR = bR * BYTE_TO_FLOAT;
fG = bG * BYTE_TO_FLOAT;
fB = bB * BYTE_TO_FLOAT;
// Convert from RGB to HSV, using float ranges 0.0 to 1.0.
float fDelta;
float fMin, fMax;
int iMax;
// Get the min and max, but use integer comparisons for slight speedup.
if (bB < bG) {
if (bB < bR) {
fMin = fB;
if (bR > bG) {
iMax = bR;
fMax = fR;
}
else {
iMax = bG;
fMax = fG;
}
}
else {
fMin = fR;
fMax = fG;
iMax = bG;
}
}
else {
if (bG < bR) {
fMin = fG;
if (bB > bR) {
fMax = fB;
iMax = bB;
}
else {
fMax = fR;
iMax = bR;
}
}
else {
fMin = fR;
fMax = fB;
iMax = bB;
}
}
fDelta = fMax - fMin;
fV = fMax; // Value (Brightness).
if (iMax != 0) { // Make sure it's not pure black.
fS = fDelta / fMax; // Saturation.
float ANGLE_TO_UNIT = 1.0f / (6.0f * fDelta); // Make the Hues between 0.0 to 1.0 instead of 6.0
if (iMax == bR) { // between yellow and magenta.
fH = (fG - fB) * ANGLE_TO_UNIT;
}
else if (iMax == bG) { // between cyan and yellow.
fH = (2.0f/6.0f) + ( fB - fR ) * ANGLE_TO_UNIT;
}
else { // between magenta and cyan.
fH = (4.0f/6.0f) + ( fR - fG ) * ANGLE_TO_UNIT;
}
// Wrap outlier Hues around the circle.
if (fH < 0.0f)
fH += 1.0f;
if (fH >= 1.0f)
fH -= 1.0f;
}
else {
// color is pure Black.
fS = 0;
fH = 0; // undefined hue
}
// Convert from floats to 8-bit integers.
int bH = (int)(0.5f + fH * 255.0f);
int bS = (int)(0.5f + fS * 255.0f);
int bV = (int)(0.5f + fV * 255.0f);
// Clip the values to make sure it fits within the 8bits.
if (bH > 255)
bH = 255;
if (bH < 0)
bH = 0;
if (bS > 255)
bS = 255;
if (bS < 0)
bS = 0;
if (bV > 255)
bV = 255;
if (bV < 0)
bV = 0;
// Set the HSV pixel components.
uchar *pHSV = (uchar*)(imHSV + y*rowSizeHSV + x*3);
*(pHSV+0) = bH; // H component
*(pHSV+1) = bS; // S component
*(pHSV+2) = bV; // V component
}
}
}
return imageHSV;
}
