The following scenario:
URL img_url = getClass().getResource("/resources/some-image.jpg");
String img_path = img_url.getPath();
if (img_path.startsWith("/")) {
img_path = img_path.substring(1);
}
Mat img = Highgui.imread(img_path);
...works fine running from NetBeans (i.e. unpacked/not built). But once I build a jar and try to run it, things are falling appart. While the call to getResource(), and in consequence to getPath(), both are fine (i.e. the file is found), the OpenCV function Highgui.imread() returns an empty Mat now.
So I highly suspect that said OpenCV function can't handle path's that point into a jar file, which look something like: "file:/C:/.../file.jar!/resources/some-image.jpg"
Any ideas?
:/
EDIT (v2; improved solution):
/**
* A utility class to get rid of annoying boilerplate code while dealing with
* the OpenCV Java API (which is generated automatically for the most part) and
* in consequence with lots of Mat's (I/O, conversions to BufferedImages and
* what not, ...).
*/
public final class OpenCVUtils {
/**
* Don't let anyone instantiate this class.
*/
private OpenCVUtils() {}
/**
* 8bit, 3-channel image.
* @see Highgui.CV_LOAD_IMAGE_COLOR
*/
public static final int LOAD_COLOR = Highgui.CV_LOAD_IMAGE_COLOR;
/**
* 8bit, 1-channel image.
* @see Highgui.CV_LOAD_IMAGE_GRAYSCALE
*/
public static final int LOAD_GRAYSCALE = Highgui.CV_LOAD_IMAGE_GRAYSCALE;
/**
* Loads an image from a file.
* This is a wrapper around Highgui.imread() which fails if the file
* is inside a jar/zip. This function takes care of that case, loads the
* image in Java and manually creates the Mat...
*
* @param name name of the resource
* @param int Flags specifying the color type of a loaded image;
* supported: LOAD_COLOR (8-bit, 3-channels),
* LOAD_GRAYSCALE (8-bit, 1-channel),
* @return Mat of type CV_8UC3 or CV_8UC1 (empty Mat is returned in case of an error)
*/
public static Mat readImage(String name, int flags) {
URL url = name.getClass().getResource(name);
// make sure the file exists
if (url == null) {
System.out.println("ResourceNotFound: " + name);
return new Mat();
}
String path = url.getPath();
// not sure why we (sometimes; while running unpacked from the IDE) end
// up with the authority-part of the path (a single slash) as prefix,
// ...anyways: Highgui.imread can't handle it, so that's why.
if (path.startsWith("/")) {
path = path.substring(1);
}
Mat image = Highgui.imread(path, flags);
// ...and if Highgui.imread() has failed, we simply assume that the file
// is packed in a jar (i.e. Java should be able to read the image)
if (image.empty()) {
BufferedImage buf;
try {
buf = ImageIO.read(url);
} catch (IOException e) {
System.out.println("IOException: " + e.getMessage());
return image;
}
int height = buf.getHeight();
int width = buf.getWidth();
int rgb, type, channels;
switch (flags) {
case LOAD_GRAYSCALE:
type = CvType.CV_8UC1;
channels = 1;
break;
case LOAD_COLOR:
default:
type = CvType.CV_8UC3;
channels = 3;
break;
}
byte[] px = new byte[channels];
image = new Mat(height, width, type);
for (int y=0; y<height; y++) {
for (int x=0; x<width; x++) {
rgb = buf.getRGB(x, y);
px[0] = (byte)(rgb & 0xFF);
if (channels==3) {
px[1] = (byte)((rgb >> 8) & 0xFF);
px[2] = (byte)((rgb >> 16) & 0xFF);
}
image.put(y, x, px);
}
}
}
return image;
}
/**
* Loads an image from a file (8-bit, 3-channels).
* This is a wrapper around Highgui.imread() which fails if the file
* is inside a jar/zip. This function takes care of that case, loads the
* image in Java and manually creates the Mat...
*
* @param name name of the resource
* @return Mat of type CV_8UC3 (empty Mat is returned in case of an error)
*/
public static Mat readImage(String name) {
return readImage(name, LOAD_COLOR);
}
/* ... */
}
...and it works too. :)
Any complaints/something wrong with this? :(
