I have 2 (aerial) images, taken from a slightly different angle:
image 1:
image2:
I need to rescale image1 in horizontal direction to align it to image2. Without any modification, both images placed next to each other look like this:
This is the desired result: (made with photoshop)
In Photoshop, I took the right half of image1 and scaled it down horizontally a little bit. I did the same for the left half of image1, where I had to scale slightly more.
I would like to know how I can accomplish this using openCV - by using Hough Line Transform. I already started drawing hough lines, but I have no idea how to do the transform to make the hough lines match:
Here's my C++ code (called from objective-c):
cv::Mat image1 = [im1 CVMat3];
cv::Mat gray_image1;
// Convert to Grayscale
cvtColor( image1, gray_image1, CV_RGB2GRAY );
cv::Mat dst1, cdst;
Canny(image1, dst1, 40, 90, 3);
double minLineLength = 0;
double maxLineGap = 10;
std::vector<cv::Vec2f> lines;
// detect lines
cv::HoughLines(dst1, lines, 1, CV_PI/180, 90, minLineLength,maxLineGap );
for( size_t i = 0; i < lines.size(); i++ ) {
float rho = lines[i][0], theta = lines[i][1];
if( theta>CV_PI/180*70 && theta<CV_PI/180*110) {
cv::Point pt1, pt2;
double a = cos(theta), b = sin(theta);
double x0 = a*rho, y0 = b*rho;
pt1.x = cvRound(x0 + 1000*(-b));
pt1.y = cvRound(y0 + 1000*(a));
pt2.x = cvRound(x0 - 1000*(-b));
pt2.y = cvRound(y0 - 1000*(a));
line( image1, pt1, pt2, cvScalar(10,100,255), 3, CV_AA);
}
}
Some help would be really appreciated :-). Thanks in advance.
Related
I have this code that basically reads each pixel of an image and redraws it with different shapes. All shapes will get faded in using a sin() wave.
Now I want to rotate every "Pixelshape" around its own axis (shapeMode(CENTER)) while they are faded in and the translate function gives me a headache in this complex way.
Here is the code so far:
void setup() {
size(1080, 1350);
shapeMode(CENTER);
img = loadImage("loremipsum.png");
…
}
void draw() {
background(123);
for (int gridX = 0; gridX < img.width; gridX++) {
for (int gridY = 0; gridY < img.height; gridY++) {
// grid position + tile size
float tileWidth = width / (float)img.width;
float tileHeight = height / (float)img.height;
float posX = tileWidth*gridX;
float posY = tileHeight*gridY;
// get current color
color c = img.pixels[gridY*img.width+gridX];
// greyscale conversion
int greyscale = round(red(c)*0.222+green(c)*0.707+blue(c)*0.071);
int gradientToIndex = round(map(greyscale, 0, 255, 0, shapeCount-1));
//FADEIN
float wave = map(sin(radians(frameCount*4)), -1, 1, 0, 2);
//translate(HEADACHE);
rotate(radians(wave));
shape(shapes[gradientToIndex], posX, posY, tileWidth * wave, tileHeight * wave);
}
}
I have tried many calculations but it just lets my sketch explode.
One that worked in another sketch where I tried basically the same but just in loop was (equivalent written):
translate(posX + tileWidth/2, posY + tileHeight/2);
I think I just don't get the matrix right? How can I translate them to its meant place?
Thank you very much #Rabbid76 – at first I just pasted in your idea and it went of crazy – then I added pushMatrix(); and popMatrix(); – turned out your translate(); code was in fact right!
Then I had to change the x and y location where every shape is drawn to 0,0,
And this is it! Now it works!
See the code here:
float wave = map(sin(radians(frameCount*4)), -1, 1, 0, 2);
pushMatrix();
translate(posX + tileWidth/2, posY + tileHeight/2);
rotate(radians(wave*180));
shape(shapes[gradientToIndex], 0, 0, tileWidth*wave , tileHeight*wave );
popMatrix();
PERFECT! Thank you so much!
rotate defines a rotation matrix and multiplies the current matrix by the rotation matrix. rotate therefore causes a rotation by (0, 0).
You have to center the rectangle around (0, 0), rotate it and move the rotated rectangle to the desired position with translate.
Since translate and rotate multiplies the current matrix by a new matrix, you must store and restore the matrix by pushMatrix() respectively popMatrix().
The center of a tile is (posX + tileWidth/2, posY + tileHeight/2):
pushMatrix();
translate(posX + tileWidth/2, posY + tileHeight/2);
rotate(radians(wave));
shape(shapes[gradientToIndex],
-tileWidth*wave/2, -tileHeight*wave/2,
tileWidth * wave, tileHeight * wave);
popMatrix();
I am trying to rotate an image in Matlab about an arbitrary set of points.
So far, I have used imrotate, but it looks like imrotate only rotates about the center.
Is there a nice way of doing this without first padding the image and then using imrotate?
Thank you
The "nice way" is using imwarp
Building the transformation matrix is a little tricky.
I figured out how to build it from a the following question: Matlab image rotation
The transformation supports rotation, translation and zoom.
Parameters:
(x0, y0) is the center point that you rotate around it.
phi is rotation angle.
sx, sy are horizontal and vertical zoom (set to value to 1).
W and H are width and height of input (and output) images.
Building 3x3 transformation matrix:
T = [sx*cos(phi), -sx*sin(phi), 0
sy*sin(phi), sy*cos(phi), 0
(W+1)/2-((sx*x0*cos(phi))+(sy*y0*sin(phi))), (H+1)/2+((sx*x0*sin(phi))-(sy*y0*cos(phi))), 1];
Using imwarp:
tform = affine2d(T);
J = imwarp(I, tform, 'OutputView', imref2d([H, W]), 'Interp', 'cubic');
Here is a complete executable code sample:
I = imresize(imread('peppers.png'), 0.5); %I is the input image
[H, W, ~] = size(I); %Height and Width of I
phi = 120*pi/180; %Rotate 120 degrees
%Zoom coefficients
sx = 1;
sy = 1;
%Center point (the point that the image is rotated around it).
x0 = (W+1)/2 + 50;
y0 = (H+1)/2 + 20;
%Draw white cross at the center of the point of the input image.
I(y0-0.5:y0+0.5, x0-19.5:x0+19.5, :) = 255;
I(y0-19.5:y0+19.5, x0-0.5:x0+0.5, :) = 255;
%Build transformation matrix.
T = [sx*cos(phi), -sx*sin(phi), 0
sy*sin(phi), sy*cos(phi), 0
(W+1)/2-((sx*x0*cos(phi))+(sy*y0*sin(phi))), (H+1)/2+((sx*x0*sin(phi))-(sy*y0*cos(phi))), 1];
tform = affine2d(T);
J = imwarp(I, tform, 'OutputView', imref2d([H, W]), 'Interp', 'cubic');
%Draw black cross at the center of the output image:
J(end/2:end/2+1, end/2-15:end/2+15, :) = 0;
J(end/2-15:end/2+15, end/2:end/2+1, :) = 0;
%Shows that the center of the output image is the point that the image was rotated around it.
figure;imshow(J)
Input image:
Output image:
Note:
Important advantage over other methods (like imrotate after padding), is that the center coordinates don't have to be integer values.
You can rotate around (100.4, 80.7) for example.
I'm using processing, and I'm trying to create a circle from the pixels i have on my display.
I managed to pull the pixels on screen and create a growing circle from them.
However i'm looking for something much more sophisticated, I want to make it seem as if the pixels on the display are moving from their current location and forming a turning circle or something like this.
This is what i have for now:
int c = 0;
int radius = 30;
allPixels = removeBlackP();
void draw {
loadPixels();
for (int alpha = 0; alpha < 360; alpha++)
{
float xf = 350 + radius*cos(alpha);
float yf = 350 + radius*sin(alpha);
int x = (int) xf;
int y = (int) yf;
if (radius > 200) {radius =30;break;}
if (c> allPixels.length) {c= 0;}
pixels[y*700 +x] = allPixels[c];
updatePixels();
}
radius++;
c++;
}
the function removeBlackP return an array with all the pixels except for the black ones.
This code works for me. There is an issue that the circle only has the numbers as int so it seems like some pixels inside the circle won't fill, i can live with that. I'm looking for something a bit more complex like I explained.
Thanks!
Fill all pixels of scanlines belonging to the circle. Using this approach, you will paint all places inside the circle. For every line calculate start coordinate (end one is symmetric). Pseudocode:
for y = center_y - radius; y <= center_y + radius; y++
dx = Sqrt(radius * radius - y * y)
for x = center_x - dx; x <= center_x + dx; x++
fill a[y, x]
When you find places for all pixels, you can make correlation between initial pixels places and calculated ones and move them step-by-step.
For example, if initial coordinates relative to center point for k-th pixel are (x0, y0) and final coordinates are (x1,y1), and you want to make M steps, moving pixel by spiral, calculate intermediate coordinates:
calc values once:
r0 = Sqrt(x0*x0 + y0*y0) //Math.Hypot if available
r1 = Sqrt(x1*x1 + y1*y1)
fi0 = Math.Atan2(y0, x0)
fi1 = Math.Atan2(y1, x1)
if fi1 < fi0 then
fi1 = fi1 + 2 * Pi;
for i = 1; i <=M ; i++
x = (r0 + i / M * (r1 - r0)) * Cos(fi0 + i / M * (fi1 - fi0))
y = (r0 + i / M * (r1 - r0)) * Sin(fi0 + i / M * (fi1 - fi0))
shift by center coordinates
The way you go about drawing circles in Processing looks a little convoluted.
The simplest way is to use the ellipse() function, no pixels involved though:
If you do need to draw an ellipse and use pixels, you can make use of PGraphics which is similar to using a separate buffer/"layer" to draw into using Processing drawing commands but it also has pixels[] you can access.
Let's say you want to draw a low-res pixel circle circle, you can create a small PGraphics, disable smoothing, draw the circle, then render the circle at a higher resolution. The only catch is these drawing commands must be placed within beginDraw()/endDraw() calls:
PGraphics buffer;
void setup(){
//disable sketch's aliasing
noSmooth();
buffer = createGraphics(25,25);
buffer.beginDraw();
//disable buffer's aliasing
buffer.noSmooth();
buffer.noFill();
buffer.stroke(255);
buffer.endDraw();
}
void draw(){
background(255);
//draw small circle
float circleSize = map(sin(frameCount * .01),-1.0,1.0,0.0,20.0);
buffer.beginDraw();
buffer.background(0);
buffer.ellipse(buffer.width / 2,buffer.height / 2, circleSize,circleSize);
buffer.endDraw();
//render small circle at higher resolution (blocky - no aliasing)
image(buffer,0,0,width,height);
}
If you want to manually draw a circle using pixels[] you are on the right using the polar to cartesian conversion formula (x = cos(angle) * radius, y = sin(angle) * radius).Even though it's focusing on drawing a radial gradient, you can find an example of drawing a circle(a lot actually) using pixels in this answer
I'm looking for few days a solution to draw rectangle on image frame. Basically I'm using CvInvoke.cvRectangle method to draw rectangle on image because I need antialiased rect.
But problem is when I need to rotate a given shape for given angle. I can't find any good solution.
I have tryed to draw rectangle on separate frame then rotate hole frame and apply this new image on top of my base frame. But in this solution there is a problem with antialiasing. It's not working.
I'm working on simple application that should allow draw few kinds of shape, resize them and rotation for given angle.
Any idea how to achive this?
The best way I found to draw a minimum enclosing rectangle on the contour is using the Polylines() function which uses vertices that are returned from MinAreaRect() function. There are surely other ways to do it as well. Here is the code walk down:
// Find contours
var contours = new Emgu.CV.Util.VectorOfVectorOfPoint();
Mat hierarchy = new Mat();
CvInvoke.FindContours(image, contours, hierarchy, RetrType.Tree, ChainApproxMethod.ChainApproxSimple);
// According to your metric, get an index of the contour you want to find the min enclosing rectangle for
int index = 2; // Say, 2nd index works for you.
var rectangle = CvInvoke.MinAreaRect(contours[index]);
Point[] vertices = Array.ConvertAll(rectangle.GetVertices(), Point.Round);
CvInvoke.Polylines(image, vertices, true, new MCvScalar(0, 0, 255), 5);
The result can be visualized in the image below, in red is the minimum enclosing rectangle.
I use C# and EMGU.CV(4.1), and I think this code will not be difficult to transfer to any platform.
Add function in the in your helper:
public static Mat DrawRect(Mat input, RotatedRect rect, MCvScalar color = default(MCvScalar),
int thickness = 1, LineType lineType = LineType.EightConnected, int shift = 0)
{
var v = rect.GetVertices();
var prevPoint = v[0];
var firstPoint = prevPoint;
var nextPoint = prevPoint;
var lastPoint = nextPoint;
for (var i = 1; i < v.Length; i++)
{
nextPoint = v[i];
CvInvoke.Line(input, Point.Round(prevPoint), Point.Round(nextPoint), color, thickness, lineType, shift);
prevPoint = nextPoint;
lastPoint = prevPoint;
}
CvInvoke.Line(input, Point.Round(lastPoint), Point.Round(firstPoint), color, thickness, lineType, shift);
return input;
}
This draws roteted rectangle by points. Here used rounding points by method Point.Round becose RotatedRect has points in float coordinates and CvInvoke.Line takes points as integer.
Use:
var mat = Mat.Zeros(200, 200, DepthType.Cv8U, 3);
mat.GetValueRange();
var rRect = new RotatedRect(new PointF(100, 100), new SizeF(100, 50), 30);
DrawRect(mat, rRect,new MCvScalar(255,0,0));
var brect = CvInvoke.BoundingRectangle(new VectorOfPointF(rRect.GetVertices()));
CvInvoke.Rectangle(mat, brect, new MCvScalar(0,255,0), 1, LineType.EightConnected, 0);
Result:
You should read the OpenCV documentation.
There is a RotatedRectangle class that you can use for your task. You can specify the angle by which the rectangle will be rotated.
Here is a sample code (taken from the docs) for drawing a rotated rectangle:
Mat image(200, 200, CV_8UC3, Scalar(0));
RotatedRect rRect = RotatedRect(Point2f(100,100), Size2f(100,50), 30);
Point2f vertices[4];
rRect.points(vertices);
for (int i = 0; i < 4; i++)
line(image, vertices[i], vertices[(i+1)%4], Scalar(0,255,0));
Rect brect = rRect.boundingRect();
rectangle(image, brect, Scalar(255,0,0));
imshow("rectangles", image);
waitKey(0);
Here is the result:
I have tried this code. 540 is the left most x value of the box,3 is left most y value of the box,262 - width ,23 -height of the region which I am going to calculate the ratio of the white/black pixels. What I really wanted to do is detect the number of white/black pixel ratio in a specific region.I have calculate the coordinates for each cell (regions which I am going to specified)and try with this code.But the error in counting.
Can I please have an idea about this issue please..
I am really stuck here with my final year project.
CvSize cvSize = cvSize(img.width(), img.height());
IplImage image = cvCreateImage(cvSize, IPL_DEPTH_8U, 1);
IplImage image2 = cvCreateImage(cvSize, IPL_DEPTH_8U, 3);
cvCvtColor(image2, image, CV_RGB2GRAY);
cvSetImageROI(image2, cvRect(540,3,262,23));
//IplImage image2 = cvCreateImage(cvSize, IPL_DEPTH_8U, 3);
//
//cvCvtColor(arg0, arg1, arg2)
// cvCvtColor(image2, image, CV_RGB2GRAY);
//cvThreshold(image, image, 128, 255, CV_THRESH_BINARY);
CvLineIterator iterator = new CvLineIterator();
double sum = 0, green_sum = 0, red_sum = 0;
CvPoint p2 = new CvPoint(802,3);
CvPoint p1 = new CvPoint(540,26);
int lineCount = cvInitLineIterator(image2, p1, p2, iterator, 8, 0 );
for (int i = 0; i < lineCount; i++) {
sum += iterator.ptr().get() & 0xFF;
}
System.out.println("sum................"+sum);
CV_NEXT_LINE_POINT(iterator);
}
}
it gave the result as sum................0.0
I have really stuck with this..can you please give any solution for this issue please
Move CV_NEXT_LINE_POINT(iterator); line inside the for loop. Then it should work.