Develop Reference

How to align ROI bounding rectangle to main image coordinate

I'am decoding a QR code from an image, since the image is large and have other unwanted graphics I'm drawing an roi around the code and decoding it. Everything works, but when i try to draw a bounding box around the QR code, it is drawn somewhere else. How can I align the rectangle in the same area of the main image?
This is what im getting - The red rectangle is the roi, the green one is the bounding box.
Here is the code :
Image<Gray, byte> Gray_Image = My_Image.Convert<Gray, byte>();
Gray_Image.ROI = Coderect;
Gray_Image._Not();
CvInvoke.cvThreshold(Gray_Image,Gray_Image,50,255.0,Emgu.CV.CvEnum.THRESH.CV_THRESH_BINARY);
Gray_Image.Dilate(5);
StructuringElementEx element = new StructuringElementEx(3, 3, 1, 1, Emgu.CV.CvEnum.CV_ELEMENT_SHAPE.CV_SHAPE_RECT);
CvInvoke.cvMorphologyEx(Gray_Image, Gray_Image, IntPtr.Zero, element, Emgu.CV.CvEnum.CV_MORPH_OP.CV_MOP_CLOSE, 18);
var contour = Gray_Image.FindContours(Emgu.CV.CvEnum.CHAIN_APPROX_METHOD.CV_CHAIN_APPROX_SIMPLE, Emgu.CV.CvEnum.RETR_TYPE.CV_RETR_EXTERNAL);
CvInvoke.cvRectangle(My_Image, new Point(contour.BoundingRectangle.X, contour.BoundingRectangle.Y), new Point(contour.BoundingRectangle.X + contour.BoundingRectangle.Width, contour.BoundingRectangle.Y + contour.BoundingRectangle.Height), new MCvScalar(0, 255, 0), 4, Emgu.CV.CvEnum.LINE_TYPE.EIGHT_CONNECTED, 0);
pictureBox1.Image = My_Image.Bitmap;

I found the solution.
Since I know the (roiX,roiY) of the roi and i also know the (bbX,bbY,bbW,bbH) of the bounding box.
By adding the X of roi and X of bounding box i got the X of the location, similarly for Y.
I simply had to do the following :
cvInvoke.cvRectangle(My_Image, new Point(roiX+bbX, roiY+bbY), new Point((roiX+bbX)+bbW,(roiY+bbY)+bbH), new McvScalar(0,255,0), Line_Type.Eight_Connected,0);

Shift Emgu.CV.Image to the right using WarpAffine()

my goal is, to shift an Image an x-amount of pixels to the right. I guess this can be achieved by using WarpAffine. This is at least what my reseach tells me. I used quite a variety of different approaches, like:
CvInvoke.WarpAffine(realImage, transformedImage, transformationMatrix, new Size(realImage.Size);
//or while m is the Mat used to create realImage
transImage.WarpAffine(m,Emgu.CV.CvEnum.Inter.Area,Emgu.CV.CvEnum.Warp.Default,Emgu.CV.CvEnum.BorderType.Default,new Gray());
I get the Exeption:
Exception thrown: 'Emgu.CV.Util.CvException' in Emgu.CV.Platform.NetStandard.dll
[ WARN:0] global E:\bb\cv_x86\build\opencv\modules\videoio\src\cap_msmf.cpp (436) `anonymous-namespace'::SourceReaderCB::~SourceReaderCB terminating async callback
I guess I am using it the wrong way, but there is no suiting example online for me to learn from.
Does anyone has a clean way to explain it to me?
Thank you in advance!

If you are shifting the pixels x amount to the right, I assume that there would be black empty pixels on the left side? If so, you could create an ROI and cut off some pixels on the right, since you are shifting all pixels to the right, and copy the image onto another image.
//The image that you want to shift pixels with
Image<Bgr, byte> inputImage = new Image<Bgr, byte>(1000, 1000);
//The output image
Image<Bgr, byte> image = new Image<Bgr, byte>(990, 1000);
//Create the roi, with 10 pixels cut off from the right side because of the shift
inputImage.ROI = new Rectangle(0, 0, inputImage.Width - 10, inputImage.Height);
inputImage.CopyTo(image);
CvInvoke.ImShow("The Output", image);
CvInvoke.WaitKey(0);
EDIT
Now lets say you want to keep that black stripe on the left side of the image as well. Doing this is very similar to the code above, but only with a few modifications.
//The image that you want to shift pixels with
Image<Bgr, byte> inputImage = new Image<Bgr, byte>(1000, 1000);
//The output image
Image<Bgr, byte> image = new Image<Bgr, byte>(1000, 1000);
//Create the roi, with 10 pixels cut off from the right side because of the shift
inputImage.ROI = new Rectangle(0, 0, inputImage.Width - 10, inputImage.Height);
//The image we want to shift, the same one we created a ROI with,
//has the dimensions 990 X 1000 and the output image has
//dimensions of 1000 x 1000. Unfortunately, in order to paste
//an image onto another image, they need to be the same dimensions.
//How do we do this? We must create an ROI with the output image
//that has the same dimensions as the input image.
image.ROI = new Rectangle(10, 0, image.Width, image.Height);
//Now we can past the image onto the output because the dimensions match
inputImage.CopyTo(image);
//Inorder to make our output seem normal, we must empty the ROI of the output image
image.ROI = Rectangle.Empty;
CvInvoke.ImShow("The Output", image);
CvInvoke.WaitKey(0);

Emgucv turn the black background transparent

I'm very new to Emgucv, so need a little help?
The code below is mainly taken from various places from Google. It will take a jpg file (which has a green background) and allow, from a separate form to change the values of h1 and h2 settings so as to create (reveal) a mask.
Now what I want to be able to do with this mask is to turn it transparent.
At the moment it will just display a black background around a person (for example), and then saves to file.
I need to know how to turn the black background transparent, if this is the correct way to approach this?
Thanks in advance.
What I have so far is in C# :
imgInput = new Image<Bgr, byte>(FileName);
Image<Hsv, Byte> hsvimg = imgInput.Convert<Hsv, Byte>();
//extract the hue and value channels
Image<Gray, Byte>[] channels = hsvimg.Split(); // split into components
Image<Gray, Byte> imghue = channels[0]; // hsv, so channels[0] is hue.
Image<Gray, Byte> imgval = channels[2]; // hsv, so channels[2] is value.
//filter out all but "the color you want"...seems to be 0 to 128 (64, 72) ?
Image<Gray, Byte> huefilter = imghue.InRange(new Gray(h1), new Gray(h2));
// TURN IT TRANSPARENT somewhere around here?
pictureBox2.Image = imgInput.Copy(mask).Bitmap;
imgInput.Copy(mask).Save("changedImage.png");

I am not sure I really understand what you are trying to do. But a mask is a binary object. A mask is usually black for what you do not want and white for what you do. As far as I know, there is no transparent mask, as to me that makes no sense. Masks are used to extract parts of an image by masking out the rest.
Maybe you could elaborate on what it is you want to do?
Doug

I think I may have the solution I was looking for. I found some code on stackoverflow which I've tweaked a little :
public Image<Bgra, Byte> MakeTransparent(Image<Bgr, Byte> image, double r1, double r2)
{
Mat imageMat = image.Mat;
Mat finalMat = new Mat(imageMat.Rows, imageMat.Cols, DepthType.Cv8U, 4);
Mat tmp = new Mat(imageMat.Rows, imageMat.Cols, DepthType.Cv8U, 1);
Mat alpha = new Mat(imageMat.Rows, imageMat.Cols, DepthType.Cv8U, 1);
CvInvoke.CvtColor(imageMat, tmp, ColorConversion.Bgr2Gray);
CvInvoke.Threshold(tmp, alpha, (int)r1, (int)r2, ThresholdType.Binary);
VectorOfMat rgb = new VectorOfMat(3);
CvInvoke.Split(imageMat, rgb);
Mat[] rgba = { rgb[0], rgb[1], rgb[2], alpha };
VectorOfMat vector = new VectorOfMat(rgba);
CvInvoke.Merge(vector, finalMat);
return finalMat.ToImage<Bgra, Byte>();
}
I'm now looking at adding SmoothGaussian to the mask to create a kind on blend, where the two images are layered, rather than a sharp cut-out.

Remove the black background color of a bitmap

I need to remove the black background color of a bitmap in C# VS2013.
It is just like that I draw some points on a canvas. The canvas is black and I just need to change the canvas to be transparent meanwhile keeping colorful points on it without any changes.
I got the solution at:
How to remove white background color from Bitmap
Bitmap capcha = new Bitmap(#"C:/image.png");
capcha.MakeTransparent(Color.Black);
But, the background still have a gray color like a fog covering the points on the image.
How to remove it ?
UPDATE
I used the code:
ImageAttribute imageAttribute = new ImageAttribute();
imageAttribute.SetGamma(0.5f, ColorAdjustType.Bitmap);
gr.DrawImage(img, new Rectangle(0, 0, img.Width, img.Height),
0, 0, img.Width, img.Height, GraphicsUnit.Pixel, imageAttribute );
I got same thing.
More update of C# code to draw an image :
System.Drawing.Bitmap canvasImage = new System.Drawing.Bitmap(xSize, ySize, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
canvasImage.MakeTransparent(Color.Black);
Graphics g = Graphics.FromImage(canvasImage);
System.Drawing.Bitmap tempImage = myDrawImageFunction(myPoints);
g.Clear(Color.Transparent); // this only give me an empty image without any points on it. But, if I uncomment it, I will have an image with black background.
// my understanding about g.DrawImage() is to draw points on tempImage
// after clearing the background. But, the image still have a foggy covering on the image.
g.DrawImage(tempImage, new System.Drawing.PointF(x_position, y_position));
I want to have a transparent background for "tempImage" before any points are drawn on it.
The example image has a back ground that needs to be removed but the colorful points on the image need to be kept without any changes.

This will do the job:
public Color MakeTransparent(Color c, int threshold)
{ // calculate the weighed brightness:
byte val = (byte)((c.R * 0.299f + c.G * 0.587f + c.B * 0.114f));
return val < threshold ? Color.FromArgb(0, c.R, c.G, c.B) : c;
}
You could use it in a double loop over the pixels, but for fast results you should call it from the code in this post (second part!) which uses LockBits.
Change this
ModifyHue hueChanger = new ModifyHue(MaxChannel);
to the new function:
ModifyHue hueChanger = new ModifyHue(MakeTransparent);
and call it with a suitable threshold, maybe 10 or 20..:
c = hueChanger(c, 20);
The function skips the call to the system's MakeTransparent function and directly sets the alpha channel of each pixel to 0.
If you want to create a uniform color instead of a transparent one it should be easy to modify (e.g. by returning Color.FromArgb(255, 0, 0, 0) for solid black)
Do note that, while the code in the linked post takes both 24 and 32 bbp formats you should definitely not save as JPG, as this will re-introduce artifacts and the result will not work well with e.g. a TransparencyKey color..
Instead do save it as PNG, as Hans suggests!
I hope you can modify the button code to a function :-)

Cropping a cross rectangle from image using c#

What I want to do is basically cropping a rectangle from an image. However, it should satisfy some special cases:
I want to crop an angled rectangle on image.
I don't want to rotate the image and crop a rectangle :)
If cropping exceeds the image size, I don't want to crop an empty background color.
I want to crop from back of the starting point, that will end at starting point when rectangle size completed. I know I couldn't explain well so if I show what I want visually:
The blue dot is the starting point there, and the arrow shows cropping direction. When cropping exceeds image borders, it will go back to the back of the starting point as much as, when the rectangle width and height finished the end of the rectangle will be at starting point.
Besides this is the previous question I asked:
How to crop a cross rectangle from an image using c#?
In this question, I couldn't predict that a problem can occur about image dimensions so I didn't ask for it. But now there is case 3. Except case three, this is exactly same question. How can I do this, any suggestions?

What needs to be done is to add offsets to the matrix alignment. In this case I am taking one extra length of the rectangle from each side (total 9 rectangles) and offsetting the matrix each time.
Notice that it is necessary to place offset 0 (the original crop) last, otherwise you will get the wrong result.
Also note that if you specify a rectangle that is bigger than the rotated picture you will still get empty areas.
public static Bitmap CropRotatedRect(Bitmap source, Rectangle rect, float angle, bool HighQuality)
{
int[] offsets = { -1, 1, 0 }; //place 0 last!
Bitmap result = new Bitmap(rect.Width, rect.Height);
using (Graphics g = Graphics.FromImage(result))
{
g.InterpolationMode = HighQuality ? InterpolationMode.HighQualityBicubic : InterpolationMode.Default;
foreach (int x in offsets)
{
foreach (int y in offsets)
{
using (Matrix mat = new Matrix())
{
//create the appropriate filler offset according to x,y
//resulting in offsets (-1,-1), (-1, 0), (-1,1) ... (0,0)
mat.Translate(-rect.Location.X - rect.Width * x, -rect.Location.Y - rect.Height * y);
mat.RotateAt(angle, rect.Location);
g.Transform = mat;
g.DrawImage(source, new Point(0, 0));
}
}
}
}
return result;
}
To recreate your example:
Bitmap source = new Bitmap("C:\\mjexample.jpg");
Bitmap dest = CropRotatedRect(source, new Rectangle(86, 182, 87, 228), -45, true);