Multimedia Programming 03: Point Processing Departments of Digital Contents Sang Il Park

Outline Review Image Processing –Brightness –Contrast –Gamma QnA for the program assignment #1

Review IplImage cvLoadImage (file_name) cvCreateImage (size, depth, channels) cvSaveImage (file_name, image) cvReleaseImage (image) cvNamedWindow (window_name) cvShowImage (window_name, image) cvDestroyWindow (window_name) int cvWaitKey (delay) Scalar cvGet2D (image, y, x) cvSet2D (image, y, x, Scalar)

Review: HelloCV2.cpp int main(int argc, CHAR* argv[]) { IplImage * img; img = cvLoadImage("d:\\test.jpg"); cvNamedWindow("window"); cvShowImage("window", img); cvWaitKey(); IplImage * img2; img2 = cvCreateImage(cvSize(300,300), IPL_DEPTH_8U, 3); int x,y; for(x=0; x<300; x++) for(y=0; y<300; y++) { CvScalar s = cvGet2D(img, y,x); s.val[0] +=80; s.val[1] +=80; s.val[2] +=80; cvSet2D(img2,y,x,s); } cvShowImage("window", img2); cvWaitKey(); cvDestroyWindow("window"); cvReleaseImage(&img); cvReleaseImage(&img2); return 0; }

Review: HelloCV2.cpp IplImage * img; img = cvLoadImage("d:\\test.jpg"); cvNamedWindow("window"); cvShowImage("window", img); cvWaitKey();

Review: HelloCV2.cpp int main(int argc, CHAR* argv[]) { IplImage * img; img = cvLoadImage("d:\\test.jpg"); cvNamedWindow("window"); cvShowImage("window", img); cvWaitKey(); IplImage * img2; img2 = cvCreateImage(cvSize(300,300), IPL_DEPTH_8U, 3); int x,y; for(x=0; x<300; x++) for(y=0; y<300; y++) { CvScalar s = cvGet2D(img, y,x); s.val[0] +=80; s.val[1] +=80; s.val[2] +=80; cvSet2D(img2,y,x,s); } cvShowImage("window", img2); cvWaitKey(); cvDestroyWindow("window"); cvReleaseImage(&img); cvReleaseImage(&img2); return 0; }

Review: HelloCV2.cpp IplImage * img2; img2 = cvCreateImage(cvSize(300,300), IPL_DEPTH_8U, 3); int x,y; for(x=0; x<300; x++) for(y=0; y<300; y++) { CvScalar s = cvGet2D(img, y,x); s.val[0] +=80; s.val[1] +=80; s.val[2] +=80; cvSet2D(img2,y,x,s); } cvShowImage("window", img2); cvWaitKey();

Review: HelloCV2.cpp int main(int argc, CHAR* argv[]) { IplImage * img; img = cvLoadImage("d:\\test.jpg"); cvNamedWindow("window"); cvShowImage("window", img); cvWaitKey(); IplImage * img2; img2 = cvCreateImage(cvSize(300,300), IPL_DEPTH_8U, 3); int x,y; for(x=0; x<300; x++) for(y=0; y<300; y++) { CvScalar s = cvGet2D(img, y,x); s.val[0] +=80; s.val[1] +=80; s.val[2] +=80; cvSet2D(img2,y,x,s); } cvShowImage("window", img2); cvWaitKey(); cvDestroyWindow("window"); cvReleaseImage(&img); cvReleaseImage(&img2); return 0; }

Review: HelloCV2.cpp cvDestroyWindow("window"); cvReleaseImage(&img); cvReleaseImage(&img2);

Image Processing 1 Point processing Alexei Efros

Images as functions Alexei Efros

Image Processing An image processing operation typically defines a new image g in terms of an existing image f. We can transform either the range of f. Or the domain of f: What kinds of operations can each perform? Alexei Efros

Image Processing image filtering: change range of image g(x) = h(f(x)) f x h f x f x h f x image warping: change domain of image g(x) = f(h(x)) Alexei Efros

Image Processing image filtering: change range of image g(x) = h(f(x)) image warping: change domain of image g(x) = f(h(x)) h fg h f g Alexei Efros

Point Processing The simplest kind of range transformations are these independent of position x,y: g = t(f) This is called point processing. What can they do? What’s the form of t? Important: every pixel for himself – spatial information completely lost! Alexei Efros

Basic Point Processing input output picture from g = Af + B A = 1 B = 0

Basic Point Processing input output Brightness + g = Af + B A = 1 B > 0

Basic Point Processing input output Brightness – g = Af + B A = 1 B < 0

Basic Point Processing input output Contrast + (brightness +) g = Af + B A > 1 B = 0

Basic Point Processing input output Contrast + g = Af + B A > 1 B < 0 Contrast + (brightness -)

Basic Point Processing input output Contrast – g = Af + B A < 1 B > 0

Basic Point Processing input output Contrast – (brightness +) g = Af + B A < 1 B > 0+++

A coding exercise Open image and adjust brightness/contrast by pressing keyboard example)1 : brightness up(+10) 2: brightness down(-10) 3 : contrast up(+0.1)4: contrast down(-0.1) input output g = Af + B g = input color value f = output color value A = contrast value ( 초기값 = 1) B = brightness value ( 초기값 = 0)

Hint for the exercise How to get the key input? –int cvWaitKey( int delay=0 ) waits for a pressed key. After waiting for the given delay, it proceeds. Zero delay means waiting forever until user input. Delay in milliseconds.

More functions?

Power-law transformations

Image Enhancement

Example: Gamma Correction

Contrast Stretching

Programming Assignment #1 How to compare R,G,B channels? No right answer –Sum of Squared Differences (SSD): –Will it be enough? Change in size Change in brightness

In the next class… Point Processing2: –Image Histogram –FILTER Blur Noise removal Unsharp –Pixelation