Hello guys.I want to remove black/shadows regions of coloured image and after this improve contrast and brightness.
So how can i achieve this one?
Can i use equalizeHist or AdaptiveTreshold and after that,convert back to Coloured Image ?
Or what technique i can use to achieve my goal?
Thanks!
Do you want to cut (collapse to black) dark regions or remove (restore image) shadows ?
Shadow removal is a complex task. Use "shadow" in the search box here to read about this subject .
I don't know if @thienlamnhan 's code for detect shadow works. In addiction read this:
Use histEqualization to enhance bright vs dark region.
To collapse dark regions to full black you could use same principle of brightness and contrast normalization
cvtColor(src, gray, CV_BGR2GRAY);
// get full available range
double minGray,maxGray;
cv::minMaxLoc(gray, &minGray, &maxGray);
//suppose current range is 30...220
bool useRelative = true;
if(useRelative)
{
// Relative clipping dark range to black
double clipPercent = 10;
minGray = cvRound(minGray * (1 + clipPercent/100.0) );
//all below minGray+10% will become black
}
else
{
//absolute clipping. Use a fixed lower bound for dark regions
double minGrayWanted = 50;
minGray = minGrayWanted;
//all below 50 will become black
}
// current range
float inputRange = maxGray - minGray;
alpha = 255.0 / inputRange; // alpha expands current range. MaxGray will be 255
beta = -minGray * alpha; // beta shifts current range so that minGray will go to 0
src.convertTo(dst, -1, alpha, beta);
Result will be:
src[0...minGray] -> dst[0]
src[minGray...maxGray] -> src[0...255]
[EDIT] from user comment It seems that needs is to correct nonuniform illumination. In this case MORPH_TOPHAT can do the job. See my answer on this subject.
@pklab yes,but when i tried to implement this in java,my result was -> fully black image :). The problem is,that function minMaxLoc(java version) on input,have parametr: 1) Mat; 2) second variant of method have two parametrs on input : Mat,Mat. And how to get minGray value?(Because its zero by default).
@pklab thanks you so much! So i tried your algorithm and i have strange result. My examples :
source Image -> result
So you can see,that dark regions remains "dark"(but with little bit improved light) and lighter regions are getting more brightness.
Thanks!
@pklab also,how you think,this histogram equalization for coloured images is good idea to improve light and contrast?
You can find the the implementation for non uniform illumination correction at the suggested link. There is result using your source image .
To know about Gamma check this.
Please if answer it's fine for you accept it or refine your question about same subject. Open new question for other subject.
Asked: 2015-12-04 13:23:42 -0600
Seen: 21,187 times
Last updated: Dec 11 '15
