The first thing is that I am a beginner. Okay?
I've read related answers and questions, but please help me with this problem:
How can I open an JPEG image file in C++, convert it to a grayscale image, get its histogram, resize it to a smaller image, crop a particular area of it, or show a particular area of it?
For these tasks, is C or C++ faster in general?
What libraries are simplest and fastest? The running time is very important.
Thanks.
here is an example using magick library.
program which reads an image, crops it, and writes it to a new file (the exception handling is optional but strongly recommended):
#include <Magick++.h> #include <iostream> using namespace std; using namespace Magick; int main(int argc,char **argv) { // Construct the image object. Seperating image construction from the // the read operation ensures that a failure to read the image file // doesn't render the image object useless. Image image; try { // Read a file into image object image.read( "girl.jpeg" ); // Crop the image to specified size (width, height, xOffset, yOffset) image.crop( Geometry(100,100, 100, 100) ); // Write the image to a file image.write( "x.jpeg" ); } catch( Exception &error_ ) { cout << "Caught exception: " << error_.what() << endl; return 1; } return 0; } well for basic image manipulations you could also try Qt's QImage class (and other). This gives you basic functionality for opening, scaling, resizing, cropping, pixel manipulations and other tasks.
Otherwise you could as already said use ImageMagick or OpenCV. OpenCV provides a lot of examples with it for many image manipulation/image recognition tasks...
Hope it helps...
There are many good libraries for working with images in C and C++, none of which is clearly superior to all others. OpenCVwiki, project page has great support for some of these tasks, while ImageMagickwiki, project page is good at others. The JPEG group has its own implementation of JPEG processing functions as well. These are probably good resources to start from; the API documentation can guide you more specifically on how to use each of these.
As for whether C or C++ libraries are bound to be faster, there's no clear winner between the two. After all, you can always compile a C library in C++. That said, C++ libraries tend to be a bit trickier to pick up because of the language complexity, but much easier to use once you've gotten a good feel for the language. (I am a bit biased toward C++, so be sure to consider the source). I'd recommend going with whatever language you find easier for the task; neither is a bad choice here, especially if performance is important.
Best of luck with your project!
If running time is really important thing then you must consider image processing library which offloads processing job to GPU chip, such as:
libgd is about the easiest, lightest-weight solution.
gdImageCreateFromJpeg gdImageCopyMergeGray gdImageCopyResized Oh, and it's all C.
