I have a Mat containing text with a black background and a Mat containing a background. I want to merge the 2 Mat's so the text sits ontop of the background. Both Mats are BGR (CV_8UC3) and the same size (cols and rows).
Whats the OpenCV way of doing this?
I'm aware of a couple of functions but |= and += are changing the text colour and addWeighted() only works if I want one image to be slightly transparent. I just want to do a complete merge of the two (except not the black pixels in the text image). I'm looking for an OpenCV function rather than pixel editting myself, well a LUT would be good if thats an option.
Try this:
sourceText = yourTextImage;
sourceBackground = yourBackgroundImage;
cv::Mat textTransparent;
cv::inRange(sourceText, cv::Scalar(0,0,0), cv::Scalar(0,0,0), textTransparent);
cv::imshow("transparent pixel", textTransparent); // this should show all the transparent pixel as being white. If that's not the case, adjust the range.
std::cout << "is the transparency mask ok? Press any key with openCV window focus." << std::endl;
cv::Mat result = sourceBackground.clone();
sourceText.copyTo(sourceBackground, 255-textTransparent); // copy pixels, using the created mask.
instead you could copy the transparent pixels from the sourceBackground to the sourceText which is a bit faster because you don't need the 255-textTransparent...
Could not test the code, please tell me if there are bugs.
Related
I have a black area around my image and I want to create a mask using OpenCV C++ that selects just this black area so that I can paint it later. How can i do that without affecting the image itself?
I tried to convert the image to grayscale and then using threshold to convert it to binary, but it affects my image since the result contains black pixels from inside the image.
Another Question : if i want to crop the image instead of paint it, how can i do it??
Thanks in advance,
I would solve the problem like this:
Inverse-binarize the image with a threshold of 1 (i.e. all pixels with the value 0 are set to 1, all others to 0)
use cv::findContours to find white segments
remove segments that don't touch image borders
use cv::drawContours to draw the remaining segments to a mask.
There is probably a more efficient solution in terms of runtime efficiency, but you should be able to prototype my solution quite quickly.
I am using OpenCV 's implementation of GrabCut in order to remove the background from images. But for now the new background is black. Is there any way to make it transparent?
For now this part of the code looks like this:
Mat binMask( image.size(), CV_8UC1 );
binMask = mask & 1;
image.copyTo( result, binMask );
Can I somehow fill the binMask with transparent pixels?
I've read some tutorials for overlaying images, but I don't need a transparent image in front of my picture but behind.
I hope someone could help.
Many thanks!
Since you are using a 8UC1 image type, it's not possible to have transparent pixels.
These are allowed only if you have an alpha channel, with alpha set to 0: you must use a 4-channel image (3 for colors, 1 for alpha channel). The alpha channel is supported in file formats such as PNG, but not in JPG.
In case of masking, you don't need by the way the usage of transparent pixels, since the black ones actually correspond to 0 and they don't influence the result when you're blending two images (addWeighted for example, or also in case of bitwise_or operation).
I've an image (.jpg image), and I want to extract the background from the original image. I've googled a lot but have only found tutorials of extracting foreground image.
I've taken the code from another stackoverflow question. The code is working fine for me, and I've successfully extracted the foreground (as per my requirements). Now I want to completely remove this foreground from the original image. I want it to be something like this:-
Background = Original Image - Foreground
The empty space can be filled with black or white color. How can I achieve this?
I've tried using this technique:-
Mat background = image2 - foreground;
but it gives a complete black image.
Code:-
#include <opencv2/opencv.hpp>
#include <iostream>
using namespace cv;
using namespace std;
int main( )
{
// Open another image
Mat image;
image= cv::imread("images/abc.jpg");
Mat image2 = image.clone();
// define bounding rectangle
cv::Rect rectangle(40,90,image.cols-80,image.rows-170);
cv::Mat result; // segmentation result (4 possible values)
cv::Mat bgModel,fgModel; // the models (internally used)
// GrabCut segmentation
cv::grabCut(image, // input image
result, // segmentation result
rectangle,// rectangle containing foreground
bgModel,fgModel, // models
1, // number of iterations
cv::GC_INIT_WITH_RECT); // use rectangle
cout << "oks pa dito" <<endl;
// Get the pixels marked as likely foreground
cv::compare(result,cv::GC_PR_FGD,result,cv::CMP_EQ);
// Generate output image
cv::Mat foreground(image.size(),CV_8UC3,cv::Scalar(255,255,255));
//cv::Mat background(image.size(),CV_8UC3,cv::Scalar(255,255,255));
image.copyTo(foreground,result); // bg pixels not copied
// draw rectangle on original image
cv::rectangle(image, rectangle, cv::Scalar(255,255,255),1);
imwrite("img_1.jpg",image);
imwrite("Foreground.jpg",foreground);
Mat background = image2 - foreground;
imwrite("Background.jpg",background);
return 0;
}
Note: I'm an opencv beginner and don't have much knowledge of it right now. I shall be very thankful to you if you can either post the complete code (as required by me) or just post the lines of code and tell me where these lines of code be placed. Thanks.
P.S. This is my second question at StackOverflow.com. apologies ... if not following any convention.
Instead of copying all the pixels that are foreground, it copies all pixels which are not foreground. You can do this by using ~, which negates the mask:
image.copyTo(background,~result);
What if you //Get the pixels marked as likely background:
// Get the pixels marked as likely background
cv::compare(result,cv::GC_PR_BGD,result,cv::CMP_EQ);
Edit: The above code is missing GC_BGD pixels. Despite a more efficient answer was given, let's finish what we started:
// Get the pixels marked as background
cv::compare(result,cv::GC_BGD,result_a,cv::CMP_EQ);
// Get the pixels marked as likely background
cv::compare(result,cv::GC_PR_BGD,result_b,cv::CMP_EQ);
// Final results
result=result_a+result_b;
Just a small suggestion，#William's
answer can be written more concisely as：
result = result & 1;
in order to get the binary mask.
Maybe another example helps, in which I assumed that the middle portion of the image is definitely foreground.
So try this link.
Example
I want to create a mask operation...
I have two input images, of the same size (do they have to have the same depth/number of channels ? I'd like to be anything, likely 3 channels, CV_32FC3 or gray...) and I created a mask, of the same size (rows and cols)
cv::Mat mask = cv::Mat(image1.rows, image1.cols, CV_8UC1);
The mask is created with areas of black and white.
I would like to create a new cv::Mat, that will have image1 where mask has 1, and image2 where mask has 0.
I looked into cv::filter2D and copyTo... Also looked at addWeighted, but I don't want to blend them - the areas for each image should be completely separate. A roi would not help - the mask is likely to not contain a rectangle, but one or more polygons.
I can't find something that does what I want.
Is there any OpenCV function that combines my images based on the mask ? Or do I have to create my own, looping through rows and cols ?
Thank you.
Just use the bitwise_and() function and you're set. The references below include a full working example.
References:
How to "zero" everything within a masked part of an image in OpenCV
OpenCV bitwise_and + mask
I am using a LPDIRECT3DTEXTURE9 to hold my image.
This is the function used to display my picture.
int drawcharacter(SPRITE& person, LPDIRECT3DTEXTURE9& image)
{
position.x = (float)person.x;
position.y = (float)person.y;
sprite_handler->Draw(
image,
&srcRect,
NULL,
&position,
D3DCOLOR_XRGB(255,255,255));
return 0;
}
According to the book I have the RGB colour shown as the last parameter will not be displayed on screen, this is how you create transparency.
This works for the most part but leaves a pink line around my image and the edge of the picture. After trial and error I have found that if I go back into photoshop I can eliminate the pink box by drawing over it with the pink colour. This can be see with the ships on the left.
I am starting to think that photoshop is blending the edges of the image so that background is not all the same shade of pink though I have no proof.
Can anyone help fix this by programming or is the error in the image?
If anyone is good at photoshop can they tell me how to fix the image, I use png mostly but am willing to change if necessary.
edit: texture creation code as requested
character_image = LoadTexture("character.bmp", D3DCOLOR_XRGB(255,0,255));
if (character_image == NULL)
return 0;
You are loading a BMP image, which does not support transparency natively - the last parameter D3DCOLOR_XRGB(255,0,255) is being used to add transparency to an image which doesn't have any. The problem is that the color must match exactly, if it is off even by only one it will not be converted to transparent and you will see the near-magenta showing through.
Save your images as 24-bit PNG with transparency, and if you load them correctly there will be no problems. Also don't add the magenta background before you save them.
As you already use PNG, you can just store the alpha value there directly from Photoshop. PNG supports transparency out of the box, and it can give better appearance than what you get with transparent colour.
It's described in http://www.toymaker.info/Games/html/textures.html (for example).
Photoshop is anti-aliasing the edge of the image. If it determines that 30% of a pixel is inside the image and 70% is outside, it sets the alpha value for that pixel to 70%. This gives a much smoother result than using a pixel-based transparency mask. You seem to be throwing these alpha values away, is that right? The pink presumably comes from the way that Photoshop displays partially transparent pixels.