ImageIO.write(img,"jpg",pathtosave) JAVA 不将图像文件保存到选定的文件路径

Question

I'm using JVM 14.0.2 in VSCode IDE. The purpose of the code is to change the original input image to grayscale image and save the new gray image to the desired location.

The code runs with no exceptions and i tried to print some progress lines(System.out.println("Saving completed...");), those lines printed throughout the program where i plugged in. However, when i go to the selected filepath to search for the saved GrayScale image, i do not see the new image in the directory.

I then tried the BlueJ IDE, and the gray image was saved. Can you check if it's VSCode developing environment issue or my code issue? or I need a different class/method to edit images in VSCode? Thanks for your help.Let me know if you need more details.

public class GrayImage {
public static void main(String args[]) throws IOException {
    BufferedImage img = null;
    // read image
    try {
        File f = new File("C:\\original.jpg");
        img = ImageIO.read(f);

        // get image width and height
        int width = img.getWidth();
        int height = img.getHeight();
        BufferedImage grayimg = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
        // convert to grayscale
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                Color color = new Color(img.getRGB(x, y));
                int r = (int) color.getRed();
                int g = (int) color.getBlue();
                int b = (int) color.getGreen();
                // calculate average
                int avg = (r + g + b) / 3;
                // replace RGB value with avg
                Color newColor = new Color(avg, avg, avg, color.getAlpha());

                grayimg.setRGB(x, y, newColor.getRGB());
            }
        }
        // write image
        System.out.println("Trying to write the new image...");
        File newf = new File("H:\\gray.jpg");
        ImageIO.write(grayimg, "jpg", newf);
        System.out.println("Finished writing the new image...");
    } catch (IOException e) {
        System.out.println(e);
    }
}// main() ends here

}

Answer 1

If I understand this problem correctly, the important lesson here is that ImageIO.write(...) returns a boolean , indicating whether it succeeded or not. You should handle situations where the value is false , even if there is no exception. For reference, see the API doc .

Something like:

if (!ImageIO.write(grayimg, "JPEG", newf)) {
    System.err.println("Could not store image as JPEG: " + grayimg);
}

Now, for the reason your code does indeed work in one JRE and not in another, is probably related to the image being of type TYPE_INT_ARGB (ie. contains alpha channel). This used to work in Oracle JDK/JREs but support was removed :

Previously, the Oracle JDK used proprietary extensions to the widely used IJG JPEG library in providing optional color space support. This was used to support PhotoYCC and images with an alpha component on both reading and writing. This optional support has been removed in Oracle JDK 11.

The fix is easy; as your source is a JPEG file, it probably does not contain an alpha component anyway, so you could change to a different type with no alpha. As you want a gray image, I believe the best match would be:

BufferedImage grayimg = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_GRAY);

But TYPE_INT_RGB or TYPE_3BYTE_BGR should work too, should you later run into the same problem with color images.