I tried to set the capture format on a webcam from OpenCV’s cv2.VideoCapture and ran into a problem: it’s using the wrong IOCTL command.
So I used python-v4l2capture to get images from the device, which allows more control.
Here is the gist:
Enjoy!
Roy
Category: programming
I wasn’t able to find online a complete example on how to persist OpenCV matrices in Python (so really NumPy arrays) to YAML like what cv::FileStorage will give you.
So here’s a short snippet:
import numpy as np
import yaml
# A yaml constructor is for loading from a yaml node.
# This is taken from: http://stackoverflow.com/a/15942429
def opencv_matrix_constructor(loader, node):
mapping = loader.construct_mapping(node, deep=True)
mat = np.array(mapping["data"])
mat.resize(mapping["rows"], mapping["cols"])
return mat
yaml.add_constructor(u"tag:yaml.org,2002:opencv-matrix", opencv_matrix_constructor)
# A yaml representer is for dumping structs into a yaml node.
# So for an opencv_matrix type (to be compatible with c++'s FileStorage) we save the rows, cols, type and flattened-data
def opencv_matrix_representer(dumper, mat):
mapping = {'rows': mat.shape[0], 'cols': mat.shape[1], 'dt': 'd', 'data': mat.reshape(-1).tolist()}
return dumper.represent_mapping(u"tag:yaml.org,2002:opencv-matrix", mapping)
yaml.add_representer(np.ndarray, opencv_matrix_representer)
#example
with open('output.yaml', 'w') as f:
f.write("%YAML:1.0")
yaml.dump({"a matrix": np.zeros((10,10)), "another_one": np.zeros((2,4))}, f)
# a matrix: !!opencv-matrix
# cols: 10
# data: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
# 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
# 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
# 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
# 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
# 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
# 0.0, 0.0, 0.0, 0.0, 0.0]
# dt: d
# rows: 10
# another_one: !!opencv-matrix
# cols: 4
# data: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
# dt: d
# rows: 2
with open('output.yaml', 'r') as f:
print yaml.load(f)
# {'a matrix': array([[ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
# [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
# [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
# [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
# [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
# [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
# [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
# [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
# [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
# [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.]]), 'another_one': array([[ 0., 0., 0., 0.],
# [ 0., 0., 0., 0.]])}
There you go
Sharing a small snippet on creating a loading spinner in a Tapestry 5.3+ Mixin, using spin.js.
It creates a convenient way to add spinners to your long-loading-times ajax zone updates, with all the code hidden away from the template .tml and page class object.
Sorry I can’t show a working example, that would entail running a Tapestry application server.
But it’s very straightforward, just grab the spin.min.js and the rest falls into place (it also depends on jQuery).
I was looking for a way to get a fluid container live side-by-side with a custom width sidebar.
A custom width sidebar can’t be achieved with a Bootstrap column, and is a total mess to get right with floats if you then need a fluid container to get a grid system for the main section.
So, here’s one solution:
JSFiddle: https://jsfiddle.net/6sfog80k/
Sharing a small libjpeg snippet.
Some SO questions about it have only partial snippets:
- http://stackoverflow.com/questions/16390783/how-to-save-yuyv-raw-data-to-jpeg-using-libjpeg
- http://stackoverflow.com/questions/17029136/weird-image-while-trying-to-compress-yuv-image-to-jpeg-using-libjpeg
- http://stackoverflow.com/questions/19282402/how-to-compress-a-yuyv-image-into-a-jpeg
Enjoy!
Roy
Using Poppler, of course!
Poppler is a very useful tool for handling PDF, so I’ve discovered lately. Having tried both muPDF and ImageMagick’s Magick++ and failed, Poppler stepped up to the challenge and paid off.
So here’s a small example of how work the API (with OpenCV, naturally):
#include <iostream>
#include <fstream>
#include <sstream>
#include <opencv2/opencv.hpp>
#include <poppler-document.h>
#include <poppler-page.h>
#include <poppler-page-renderer.h>
#include <poppler-image.h>
using namespace cv;
using namespace std;
using namespace poppler;
Mat readPDFtoCV(const string& filename,int DPI) {
document* mypdf = document::load_from_file(filename);
if(mypdf == NULL) {
cerr << "couldn't read pdf\n";
return Mat();
}
cout << "pdf has " << mypdf->pages() << " pages\n";
page* mypage = mypdf->create_page(0);
page_renderer renderer;
renderer.set_render_hint(page_renderer::text_antialiasing);
image myimage = renderer.render_page(mypage,DPI,DPI);
cout << "created image of " << myimage.width() << "x"<< myimage.height() << "\n";
Mat cvimg;
if(myimage.format() == image::format_rgb24) {
Mat(myimage.height(),myimage.width(),CV_8UC3,myimage.data()).copyTo(cvimg);
} else if(myimage.format() == image::format_argb32) {
Mat(myimage.height(),myimage.width(),CV_8UC4,myimage.data()).copyTo(cvimg);
} else {
cerr << "PDF format no good\n";
return Mat();
}
return cvimg;
}
All you have to do is give it the DPI (say you want to render in 100 DPI) and a filename.
Keep in mind it only renders the first page, but getting the other pages is just as easy.
That’s it, enjoy!
Roy.
Years ago I wanted to implement PTAM. I was young and naïve 🙂
Well I got a few moments to spare on a recent sleepless night, and I set out to implement the basic bootstrapping step of initializing a map with a planar object – no known markers needed, and then tracking it for augmented reality purposes.
Just sharing a code snippet about how to implement a jQuery+Bootstrap progress bar for a background operation in Tapestry 5. There’s not a lot to it, but it took me a while and serious digging through the internet to find how to make it work. Essentially it’s based on a couple of examples and references I found:
- http://permalink.gmane.org/gmane.comp.java.tapestry.user/85776
- https://github.com/uklance/tapestry-stitch
But I simplified things because I don’t like the over-design Java can easily make you do…
You already know I love libQGLViewer. So here a snippet on how to do AR in a QGLViewer widget. It only requires a couple of tweaks/overloads to the plain vanilla widget setup (using the matrices properly, disable the mouse binding) and it works.
The major problems I recognize with getting a working AR from OpenCV’s intrinsic and extrinsic camera parameters are their translation to OpenGL. I saw a whole lot of solutions online, and I contributed from my own experience a while back, so I want to reiterate here again in the context of libQGLViewer, with a couple extra tips.