pixels and RGB of a .png file

[Mano Wilk]

hello everyone,

i started learning java last night. i had a previous little knowledge with c++, somewhere in the past.

i am doing an exercise where i load a black picture, change its RGB values and then i could see the hidden image. i have read much about filechooser and so...and finally i made it to get a little window asking me to choose a file.
now my ideas are too "loose" yet, and i am confused and dont know what to do.
I have seen many examples that do what i want.
It seems the right way is to count every pixel of the .png file? and using something similar to getRed, getBlue, getGreen for every i (means width) and j (height)?
so the idea is, e.g i have a 4x4 image, i.e 16 pixels (?) then i would use the getRed getBlue getGreen stuff to grab the RGB of each pixel? That means 16 data values?
so i would edit these 16 values, like *0,5 if i want to decrease the RGB level and so?
i cant understand how my code would ordenate all the pixels again at the end...
isnt there a way to get a data like "this is the RGB value of the image" instead of "those are the RGB values of every pixel"?
sorry if this is a too abstract question, but i dont know how to express my problem, as i said, i am rather confused.
and i apologize i dont have a code to post, but this part of the code i dont have yet. All the other parts are: creating object for the picture, loading a picture, showing a picture [here i should add the code to edit the RGB values] and then save this new picture somewhere. and i dont think they would help in this part...

[Rajdeep Biswas]

Welcome to the Ranch. Can you give some pseudocode or dumb text how you have done so far and what are the results?

[Mano Wilk]

Rajdeep Biswas wrote:Welcome to the Ranch. Thats all for now!

hello!

kind regards

[Mano Wilk]

Rajdeep Biswas wrote:Welcome to the Ranch. Can you give some pseudocode or dumb text how you have done so far and what are the results?

yes, i will try

public class ImagePuzzle {
 
    
    public void solveBlackPuzzle() {
   
	Picture input = new Picture(FileChooser.pickAFile());
	
	Picture output = null;
    
	if (input != null) {

	    input.show();	    
         ///////////////////////////////////////////////////// 
         //  HERE ARE THE THINGS DONE. i think.
        //////////////////////////////////////////////////////
            output.show();
	    String directory = "/home/wilker/";  
	    output.write(directory + "black-puzzle-solution.png");
	}
    }

so, i believe where "here are the things done" i should tell the program to the following:

method to decrease red
get the pixels;
define an integer that will work as a counter
for (int= 0; i < my pixels number; i++)
{
p = pixels[i];
value = p.getRed(); (is getRed a method from color?)
p.setRed(something....value*0,2) (is setRed a method from color?)

now it should show the picture, with the red value changed...

}

thank you

[Darryl Burke]

Mano Wilk, please BeForthrightWhenCrossPostingToOtherSites <- link
http://www.java-forums.org/new-java/67360-pixels-rgb-png-file.html#post317071
https://forums.oracle.com/forums/thread.jspa?messageID=10777646�

[Ulf Dittmer]

I'm not sure what the "Picture" class does, but I would use the javax.imageio.ImageIO class to read and write the image; it provides you with a BufferedImage object that you can use to get and set individual pixel values.

Note that the R, G, B and alpha values of a particular pixel are encoded in a single int value, so you need to do some bitwise arithmetic to extract (and later reassemble) them from the int.

[Mano Wilk]

Ulf Dittmer wrote:I'm not sure what the "Picture" class does, but I would use the javax.imageio.ImageIO class to read and write the image; it provides you with a BufferedImage object that you can use to get and set individual pixel values.

thank you for the reply!
these are the methods of Pictures:

show()
repaint()
explore() – opens a Picture explorer
Pixel [] getPixels()
Pixel getPixel(x,y)
int getWidth()
int getHeight()
writePictureTo(filename)

other class i think i should use is Pixels:

int getGreen(), getRed(), getBlue()
setGreen(value), setRed(value), setBlue(value)
Color getColor()
setColor(color)
int getX(), getY()

I am thinking in creating a pixel[i] and while i is smaller than my pixel numbers:

Pixel[] pixels = mypicture.getPixels();
x = pixels[i]
value = x.pixels[i]
x.setRed(use the value here)

Note that the R, G, B and alpha values of a particular pixel are encoded in a single int value, so you need to do some bitwise arithmetic to extract (and later reassemble) them from the int.

I see. That means my "value" could not be used as i wrote and i should interpret it using arithmetic?

thanks for your time and
kind regards