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Updating an image in Java Swing shows strange behaviour

I want to update an image in Java Swing and tried two different methods of rendering these images.
Define a JLabel and set the icon of it
Override the paintComponent(Graphics g) function in a custom JPanel and call g.drawImage(img, 0, 0, null)
Rendering the first image works as expected in both ways, but if I'm trying to update the image, it doesn't replace but renders one layer above which is a problem, because the images I want to render are semi-transparent, so you can see the others through.
I'm already using the repaint() method.
Method 1
public void setImage(Image img) {
this.backgroundLabel.setIcon(new ImageIcon(img));
this.repaint();
}
Method 2
public void setImage(Image img) {
this.img = img;
this.repaint();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(img, 0, 0, null);
}
I'm thankful for any tips! <3

The first thing line in paintComponent(Graphics g) should be
super.paintComponent(g);
This clears the panel, does any background painting if necessary, and any other support functions from the overridden paintComponent method. Otherwise, you will keep drawing images over the previous ones without first clearing them.

For anyone in the future with the same problem, here is the answer I came up with.
I didn't repainted the full frame, but only the JPanel.
I had to add
frame.repaint();
in setImage().

Background image for a jPanel not working

I am new to making GUIs so I decided to try the the windows builder for eclipse, and while great I do have some doubts. I have been searching but I cannot seen to find a good way to add a background image to my "menu". For example I tried this:
public Menu() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(50, 50, 300, 250); //Dimensiones
contentPane = new JPanel() { //Imagen de Fondo
public void paintComponent(Graphics g) {
Image img = Toolkit.getDefaultToolkit().getImage(
Menu.class.getResource("/imgs/rotom.jpg"));
g.drawImage(img, 0, 0, this.getWidth(), this.getHeight(), this);
}
};
And adding the following classes:
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
But to no avail the window remains with its dull grey color, so far my code is just the standard one WindowsBuilder cooks for you plus 4 buttons but I doubt they're of importance here. Shouldn't the code I added override the paintComponent() method of the jPanel and draw the image in it?
The class for the menu is in a package within my project and the image is within a imgs package is within the same project as well.
Thanks a lot in advance.

A simple method, if you're not interested in resizing the background image or applying any effects is to use a JLabel...
BufferedImage bg = ImageIO.read(Menu.class.getResource("/imgs/rotom.jpg"));
JLabel label = new JLabel(new ImageIcon(bg));
setContentPane(label);
setLayout(...);
There are limitations to this approach (beyond scaling), in that the preferred size of the label will always be that of the image and never take into account it's content. This is both good and bad.
The other approach, which you seem to be using, is to use a specialised component
public class BackgroundPane extends JPanel {
private BufferedImage img;
public BackgroundPane(BufferedImage img) {
this.img = img;
}
#Override
public Dimension getPreferredSize() {
return img == null ? super.getPreferredSize() : new Dimension(img.getWidth(), img.getHeight());
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(img, 0, 0, this);
}
}
You should avoid trying to perform any task in the paintComponent method which may take time to complete as paintComponent may be called often and usually in quick succession....
Getting the image to scale when the component is resized is an entire question into of it self, for some ideas, you could take a look at...
Java: maintaining aspect ratio of JPanel background image
Java: JPanel background not scaling
Quality of Image after resize very low -- Java
Reading/Loading images
Oh, and, you should avoid extending directly from top level containers, like JFrame, they reduce the reusability for your components and lock you into a single container

Zoom an Image after ActionListener

I try to create an Image View Program and have a problem in Java Image's zoom in and zoom out :D
I create a JPanel and using BufferedImage to display an image in my computer. After clicking a button, it should be zoom .
But the problem in here that, I overload the method paintComponent() in the JPanel to display a image as I want. After searching in the Google, I think I should use Graphic2D to deal with this problem. Follow on this post, the line
Graphics2D g = resizedImage.createGraphics();
g.drawImage(originalImage, 0, 0, newImageWidth , newImageHeight , null);
should be put in the overloaded method paintComponent(). Howerver, in my case, I want to zoom the image after clicking a button, so, how can i access to the paintComponent() to do the zoom ??
public class MiddlePanel extends JPanel {
private BufferedImage img;
private JButton jbtZoom = new JButton("Zoom");
public MiddlePanel(int width){
img = ImageIO.read(new FileInputStream(new File("C:\\Picture\\pic1.jpg")));
this.setPreferredSize(new Dimension(800,460));
}
public void paintComponent(Graphics g) {
g.drawImage(img......);
}
public void addComponentActionListener(){
jbtZoom.addActionListener(new ActionListener{
public void actionPerformed(){
//What should I do in here to zoom the image....
}
});
}
Thank for your help!

You need to change your design like so:
Store in a variable your zoom state and then your
overridden paintComponent method should look at that variable to
decide if/how much to zoom.
Your ActionListener will update the variable then call repaint() on
the panel.

How to put or draw stable image background in java

I'm having problems with putting a stable image background.
I successfully create/draw an image background but when I consecutively run it many times, the image is not showing. The background image seems to be not stable. When I drag the frame to a side of my laptop screen, the image is being erased. How do I create/draw a stable background image that doesn't flicker or erased when dragged?
This code below is what I used for my background image:
public void paint( Graphics g ) {
super.paint(g);
g.drawImage(img, -30, 0, null); //draw image to background
}

Use the JLabel.setIcon(Icon icon) method.
The benefit of this is you don't need to overwrite any method to put a background.
Indeed you can also use JLabel in alternative to JPanel, if you want a container that has an image background. Below can explain this trick in code:
public class JPanelWithBackground extends JLabel {
public JPanelWithBackground() {
add(new JButton("I can attached to JLabel? Isn't cool? "));
setBackgroundImage("path_to_image.png");
}
public void setBackgroundImage(String imagePath) {
setIcon(new ImageIcon(imagePath));
}
}

Using Graphics2D to Manipulate an Image Multiple Times

I am trying to figure out how to take an image and use Graphics2D to manipulate it, all while being able to do multiple operations on the same image (so darkening it twice would make it darker than doing it once). Every single example I have found, is meant to manipulate an image once and display it. I need to be able to display the image multiple times. For example, let's say I have a menu with options 1, 2, 3, etc., and 1 darkens it, 2 lightens it and 3 displays the image.
How would I achieve this? I can get the image, darken it, rotate it and display it, but not with a menu or some other way of the user choosing when and what. If someone could link me to a webpage that does just that, or write a short (shorter is better), one class program to do what I described, I should be able to get going.
Basically, I need to be able to do something like this:
initialize image;
display(image);
lighten(image);
What I don't understand, is how I manipulate the image with the Graphics2D, and have it apply to my image.
This is what I have so far(mostly from here):
import java.awt.*;
import javax.swing.*;
#SuppressWarnings("serial")
public class ShowImage extends JPanel {
Image img;
public ShowImage() {
super();
img = Toolkit.getDefaultToolkit().getImage("image.png");
}
public void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.translate(170, 0);
g2d.rotate(1);
g2d.drawImage(img, 0, 0, this);
}
public static void main(String arg[]) {
JFrame frame = new JFrame("Image Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(600, 400);
ShowImage panel = new ShowImage();
frame.setContentPane(panel);
frame.setVisible(true);
}
}
Currently, I am doing all the manipulation in paintComponent(), so it's not at all easy to manipulate. Is there a way to get the Graphics2D variable set up in the main, then get it into the paintComponent() somehow? I am completely lost as to how I would go about doing this.
I tried to post the links to all the webpages I viewed, but it won't let me post more than two links, because I am new.

If you need to manipulate an image in memory, create a BufferedImage and then call BufferedImage.createGraphics() to get access to a graphics object for drawing into the image's buffer.
When you want to render that image onto a component in the UI, use the paintComponent() method of that component as you have done. Note that this involves two separate graphics objects, used for two different purposes.