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How do I fade a BufferedImage when manipulating it's pixel data?

I am trying to do something I have never done before.
My goal is to be able to manipulate the opacity of a BufferedImage. First off, I do not use Graphics. I am developing a simple Game Engine and I only use pixel data from BufferedImages.
What have I tried?
I made my own "Image" class that takes in a BufferedImage.
BufferedImage image = null;
try {
image = ImageIO.read(Image.class.getResourceAsStream(resourcePath));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
width = image.getWidth();
height = image.getHeight();
hasAlpha = image.getColorModel().hasAlpha();
pixels = image.getRGB(0, 0, width, height,null,0,width);
After that I proceeded to my rendering code. I have a function called "drawImage()" that takes the image and it's data and then puts it out on a specific spot on the screen depending on the users wishes. I however want the user to choose it's opacity as well.
I started out by taking the pixel data for that pixel and I instead made a Color.
Color c = new Color(image.getPixels()[value2],true);
The "true" statement, what I know of, says that it should "care" about Alpha.
After that I place the pixel by using this code:
pixels[x + y * pWidth] = new Color(c.getRed(),c.getGreen(),c.getBlue(),alphaValue).getRGB();
This doesn't work. It doesnt output any errors and I can change the alphaValue to a number between 0 and infinity. However one issue I found is that it doesnt affect the image at all when I change the alpha from 255 to something like 50. It stays the same. The affect comes at 0-5. Another thing that I noticed is that when I set alphaValue to something like 2 I get an animation instead of the image with lower opacity. Sounds weird, that's why I provided a .GIF of the issue:
I guarantee you that there is no code that changes the alphaValue. During that "animation" it is set to 2 and nothing else.
So something is weird here and I wonder if you guys know the issue?
It might have something to do with the Image class and that I don't set it to BufferedImage.RGBA but I don't know how I can do so when I load an image?
If you need any more information, please leave a comment and I will provide more info!
Thanks in advance!
EDIT
I clear the screen every 1/60 of a second by manipulating the backgrounds pixels (also a bufferedImage):
public void clear() {
for(int i = 0; i < pixels.length; i++) {
pixels[i] = clearColor.getRGB();
}
}
Possible issue
I did some troubleshooting and I found out that it actually somehow increased in opacity each frame as #Joni said. Somehow the opacity or alpha seems to increase each frame but I am clearing the screen between drawings. I will troubleshoot further.
UPDATE
I made so I could move the image around and found this weird behaviour:
Link to Imgur
It seems that the "alpha" isn't reset. I know that the RGB is being reset but something is really off when it comes to the Alpha.
I changed the clear function to this:
public void clear() {
for(int i = 0; i < pixels.length; i++) {
pixels[i] = new Color(clearColor.getRed(),clearColor.getGreen(),clearColor.getBlue(),255).getRGB();
}
}
And I defined clearColor as:
Color clearColor = new Color(Color.black.getRGB(),true);
That did however not work either. Does anyone have a solution?

Your game engine is drawing the image on top of itself in a loop. After drawing it enough many times the effect is the same as not having used transparency at all. The lower the alpha, the longer it takes though: with 50% alpha you need 7 frames to get 99% opacity, with 5% alpha you need about 90 frames.
For example, suppose you are drawing a pixel value of 100 on a screen that's intially 0 (black) with 50% opacity. After the first frame, the output pixel value is .5*100 + .5*0 = 50. The second frame is drawn on top of the first frame, so the output pixel value is .5*100 + .5*50 = 75. The third frame, drawn on top of the second frame, will show .5*100 + .5*75 = 87.5.
To avoid this, you need to fill a solid background color under the image in every frame.

Exporting an image from screen(viewport) in java OpenGL

I am a newbie in OpenGL programming. I am making a java program with OpenGL. I drew many cubes inside. I now wanted to implement a screenshot function in my program but I just couldn't make it work. The situation is as follow :
I used FPSanimator to refresh my drawable in 60 fps
I drew dozens of cubes inside my Display.
I added a KeyListener to my panel, if I pressed the alt key, the program will run the following method :
public static void exportImage() {
int[] bb = new int[Constants.PanelSize.width*Constants.PanelSize.height*4];
IntBuffer ib = IntBuffer.wrap(bb);
ib.position(0);
Constants.gl.glPixelStorei(GL2.GL_UNPACK_ALIGNMENT, 1);
Constants.gl.glReadPixels(0,0,Constants.PanelSize.width,Constants.PanelSize.height,GL2.GL_RGBA,GL2.GL_UNSIGNED_BYTE,ib);
System.out.println(Constants.gl.glGetError());
ImageExport.savePixelsToPNG(bb,Constants.PanelSize.width,Constants.PanelSize.height, "imageFilename.png");
}
// Constant is a class which I store all my global variables in static type
The output in the console was 0, which means no errors. I printed the contents in the buffer and they were all zeros.
I checked the output file and it was only 1kB.
What should I do? Are there any good suggestions for me to export the screen contents to an image file using OpenGL? I heard that there are several libraries available but I don't know which one is suitable. Any help is appreciated T_T (plz forgive me if I have any grammatical mistakes ... )

You can do something like this, supposing you are drawing to the default framebuffer:
protected void saveImage(GL4 gl4, int width, int height) {
try {
GL4 gl4 = GLContext.getCurrentGL().getGL4();
BufferedImage screenshot = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics graphics = screenshot.getGraphics();
ByteBuffer buffer = GLBuffers.newDirectByteBuffer(width * height * 4);
gl4.glReadBuffer(GL_BACK);
gl4.glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
for (int h = 0; h < height; h++) {
for (int w = 0; w < width; w++) {
graphics.setColor(new Color((buffer.get() & 0xff), (buffer.get() & 0xff),
(buffer.get() & 0xff)));
buffer.get();
graphics.drawRect(w, height - h, 1, 1);
}
}
BufferUtils.destroyDirectBuffer(buffer);
File outputfile = new File("D:\\Downloads\\texture.png");
ImageIO.write(screenshot, "png", outputfile);
} catch (IOException ex) {
Logger.getLogger(EC_DepthPeeling.class.getName()).log(Level.SEVERE, null, ex);
}
}
Essentially you create a bufferedImage and a direct buffer. Then you use Graphics to render the content of the back buffer pixel by pixel to the bufferedImage.
You need an additional buffer.get(); because that represents the alpha value and you need also height - h to flip the image.
Edit: of course you need to read it when there is what you are looking for.
You have several options:
trigger a boolean variable and call it directly from the display method, at the end, when everything you wanted has been rendered
disable the automatic buffer swapping, call from the key listener the display() method, read the back buffer and enable the swapping again
call from the key listener the same code you would call in the display

You could use Robot class to take screenshot:
BufferedImage screenshot = new Robot().createScreenCapture(new Rectangle(Toolkit.getDefaultToolkit().getScreenSize()));
ImageIO.write(screenshot, "png", new File("screenshot.png"));
There are two things to consider:
You take screenshot from screen, you could determine where the cordinates of you viewport are, so you can catch only the part of interest.
Something can reside a top of you viewport(another window), so the viewport could be hided by another window, it is unlikely to occur, but it can.

When you use buffers with LWJGL, they almost always need to be directly allocated. The OpenGL library doesn't really understand how to interface with Java Arrays™, and in order for the underlying memory operations to work, they need to be applied on natively-allocated (or, in this context, directly allocated) memory.
If you're using LWJGL 3.x, that's pretty simple:
//Check the math, because for an image array, given that Ints are 4 bytes, I think you can just allocate without multiplying by 4.
IntBuffer ib = org.lwjgl.BufferUtils.createIntBuffer(Constants.PanelSize.width * Constants.PanelSize.height);
And if that function isn't available, this should suffice:
//Here you actually *do* have to multiply by 4.
IntBuffer ib = java.nio.ByteBuffer.allocateDirect(Constants.PanelSize.width * Constants.PanelSize.height * 4).asIntBuffer();
And then you do your normal code:
Constants.gl.glPixelStorei(GL2.GL_UNPACK_ALIGNMENT, 1);
Constants.gl.glReadPixels(0, 0, Constants.PanelSize.width, Constants.PanelSize.height, GL2.GL_RGBA, GL2.GL_UNSIGNED_BYTE, ib);
System.out.println(Constants.gl.glGetError());
int[] bb = new int[Constants.PanelSize.width * Constants.PanelSize.height];
ib.get(bb); //Stores the contents of the buffer into the int array.
ImageExport.savePixelsToPNG(bb, Constants.PanelSize.width, Constants.PanelSize.height, "imageFilename.png");

2D Dynamic Lighting in Java

I am making a game that has campfire objects. What I want to do is to brighten all pixels in a circle around each campfire. However, looping through every pixel and changing those within the radius is not all that efficient and makes the game run at ~7 fps. Ideas on how to either make this process efficient or simulate light differently?
I haven't written the code for the fires but this is the basic loop to check each pixel/change its brightness based on a number:
public static BufferedImage updateLightLevels(BufferedImage img, float light)
{
BufferedImage brightnessBuffer = new BufferedImage(img.getWidth(), img.getHeight(), BufferedImage.TYPE_4BYTE_ABGR);
brightnessBuffer.getGraphics().drawImage(img, 0, 0, null);
for(int i = 0; i < brightnessBuffer.getWidth(); i++)
{
for(int a = 0; a < brightnessBuffer.getHeight(); a++)
{
//get the color at the pixel
int rgb = brightnessBuffer.getRGB(i, a);
//check to see if it is transparent
int alpha = (rgb >> 24) & 0x000000FF;
if(alpha != 0)
{
//make a new color
Color rgbColor = new Color(rgb);
//turn it into an hsb color
float[] hsbCol = Color.RGBtoHSB(rgbColor.getRed(), rgbColor.getGreen(), rgbColor.getBlue(), null);
//lower it by the certain amount
//if the pixel is already darker then push it all the way to black
if(hsbCol[2] <= light)
hsbCol[2] -= (hsbCol[2]) - .01f;
else
hsbCol[2] -= light;
//turn the hsb color into a rgb color
int rgbNew = Color.HSBtoRGB(hsbCol[0], hsbCol[1], hsbCol[2]);
//set the pixel to the new color
brightnessBuffer.setRGB(i, a, rgbNew);
}
}
}
return brightnessBuffer;
}
I apologize if my code is not clean, I'm self taught.

I can give you lots of approaches.
You're currently rendering on the CPU, and you're checking every single pixel. That's hardcore brute force, and brute force isn't what the CPU is best at. It works, but as you've seen, the performance is abysmal.
I'd point you in two directions that would massively improve your performance:
Method 1 - Culling. Does every single pixel really need to have its lighting calculated? If you could instead calculate a general "ambient light", then you could paint most of the pixels in that ambient light, and then only calculate the really proper lighting for pixels closest to lights; so lights throw a "spot" effect which fades into the ambient. That way you're only ever performing checks on a few of the pixels of the screen at a time (the circle area around each light). The code you posted just looks like it paints every pixel, I'm not seeing where the "circle" dropoff is even applied.
Edit:
Instead, sweep through the lights, and just loop through local offsets of the light position.
for(Light l : Lights){
for(int x = l.getX() -LIGHT_DISTANCE, x< l.getX() + LIGHT_DISTANCE, y++){
for(int y = l.getY() - LIGHT_DISTANCE, y < l.getY() + LIGHT_DISTANCE, y++){
//calculate light
int rgb = brightnessBuffer.getRGB(x, y);
//do stuff
}
}
You may want to add a check with that method so overlapping lights don't cause a bunch of rechecks, unless you DO want that behavior (ideally those pixels would be twice as bright)
Method 2 - Offhand calculation to the GPU. There's a reason we have graphics cards; they're specifically built to be able to number crunch those situations where you really need brute force. If you can offload this process to the GPU as a shader, then it'll run licketysplit, even if you run it on every pixel several times over. This will require you to learn graphics APIs however, but if you're working in java, LibGDX makes it very painless to render using the GPU and pass off a couple shaders to the GPU.

I am uncertain about the way in which you are going about calculating light values, but I do know that using the BufferedImage.getRGB() and BufferedImage.setRGB() methods is very slow.
I would suggest accessing the pixels of the BufferedImage directly from an array (much faster IMO)
to do this:
BufferedImage lightImage = new BufferedImage(width,height,BufferedImage.TYPE_INT_ARGB);
Raster r = lightImage.getRaster();
int[] lightPixels = ((DataBufferInt)r.getDataBuffer()).getData();
Now, changing any pixel in this array will show on your image. Note that the values used in this array are color values in the format of whatever format you defined your image with.
In this case it is TYPE_INT_ARGB meaning you will have to include the alpha value in the number when setting the coloar (RRGGBB*AA*)
Since this array is a 1D array, it is more difficult to access pixels using x and y co-ordinates. The following method is an implementation of accessing pixels from the lightPixels array more easily.
public void setLight(int x, int y,int[] array,int width, int value){
array[width*y+x] = value;
}
*note: width is the width of your level, or the width of the 2D array your level might exist as, if it was a 2D array.
You can also get pixels from the lightPixels array with a similar method, just excluding the value and returning the array[width*y+x].
It is up to you how you use the setLight() and getLight() methods but in the cases that I have encountered, using this method is much faster than using getRGB and setRGB.
Hope this helps

Java's Graphics.drawImage produces an inaccurate image

I'm trying to draw one image onto another using graphics.drawImage() but it's only working accurately for some images, others it messes up. My code's below, I've made sure texture is the right image when it enters the method so that's definitely not it. Any ideas?
private BufferedImage currentSheet;
public void swapRegionWithTexture(Rectangle region, Image texture) {
Graphics sheetGraphics = currentSheet.createGraphics();
for (int ix = region.x; ix < region.x + region.width; ix++) {
for (int iy = region.y; iy < region.y + region.height; iy++) {
currentSheet.setRGB(ix, iy, 0x000000);
}
}
sheetGraphics.drawImage(texture, region.x, region.y, null);
sheetGraphics.dispose();
}
The general idea is:
Grab the graphics to draw to.
Clear out the section of the graphics that will be drawn on.
Draw the image at the given location on the graphics.
Dispose of the graphics.

Your current atomic steps are thus:
create a new buffered image
write to that buffered image some crazy manipulation of the original texture (looks like you're reversing it?)
write the original image to the current sheet.
So what if you change this
sheetGraphics.drawImage(texture, region.x, region.y, null);
to this
sheetGraphics.drawImage(bufferedTexture, region.x, region.y, null);
Otherwise you're spending time reversing the image and putting into buffered texture and then never doing anything with that buffer... so chances are you intended to use that buffered texture somewhere.

Invert bitmap colors

I have the following problem. I have a charting program, and it's design is black, but the charts (that I get from the server as images) are light (it actually uses only 5 colors: red, green, white, black and gray).
To fit with the design inversion does a good job, the only problem is that red and green are inverted also (green -> pink, red -> green).
Is there a way to invert everything except those 2 colors, or a way to repaint those colors after inversion?
And how costly are those operations (since I get the chart updates pretty often)?
Thanks in advance :)
UPDATE
I tried replacing colors with setPixel method in a loop
for(int x = 0 ;x < chart.getWidth();x++) {
for(int y = 0;y < chart.getHeight();y++) {
final int replacement = getColorReplacement(chart.getPixel(x, y));
if(replacement != 0) {
chart.setPixel(x, y, replacement);
}
}
}
Unfortunetely, the method takes too long (~650ms), is there a faster way to do it, and will setPixels() method work faster?

Manipulating a bitmap is much faster if you copy the image data into an int array by calling getPixels only once, and don't call any function inside the loop. Just manipulate the array, then call setPixels at the end.
Something like that:
int length = bitmap.getWidth()*bitmap.getHeight();
int[] array = new int[length];
bitmap.getPixels(array,0,bitmap.getWidth(),0,0,bitmap.getWidth(),bitmap.getHeight());
for (int i=0;i<length;i++){
// If the bitmap is in ARGB_8888 format
if (array[i] == 0xff000000){
array[i] = 0xffffffff;
} else if ...
}
}
bitmap.setPixels(array,0,bitmap.getWidth(),0,0,bitmap.getWidth(),bitmap.getHeight());

If you have it available as BufferedImage, you can access its raster and edit it as you please.
WritableRaster raster = my_image.getRaster();
// Edit all the pixels you wanna change in the raster (green -> red, pink -> green)
// for (x,y) in ...
// raster.setPixel(x, y, ...)
my_image.setData(raster);

OK seen that you're really only using 5 colors it's quite easy.
Regarding performances, I don't know about Android but I can tell you that in Java using setRGB is amazingly slower than getting back the data buffer and writing directly in the int[].
When I write "amazingly slower", to give you an idea, on OS X 10.4 the following code:
for ( int x = 0; x < width; x++ ) {
for ( int y = 0; y < height; y++ ) {
img.setRGB(x,y,0xFFFFFFFF);
}
}
can be 100 times (!) slower than:
for ( int x = 0; x < width; x++ ) {
for ( int y = 0; y < height; y++ ) {
array[y*width+x] = 0xFFFFFFFF;
}
}
You read correctly: one hundred time. Measured on a Core 2 Duo / Mac Mini / OS X 10.4.
(of course you need to first get access to the underlying int[] array but hopefully this shouldn't be difficult)
I cannot stress enough that the problem ain't the two for loops: in both cases it's the same unoptimized for loops. So it's really setRGB that is the issue here.
I don't know it works on Android, but you probably should get rid of setRGB if you want something that performs well.

A quick way would be to use AvoidXfermode to repaint just those colors you want changed - you could then switch between any colors you want. You just need to do something like this:
// will change red to green
Paint change1 = new Paint();
change1.setColor(Color.GREEN);
change1.setXfermode(new AvoidXfermode(Color.RED, 245, AvoidXfermode.Mode.TARGET));
Canvas c = new Canvas();
c.setBitmap(chart);
c.drawRect(0, 0, width, height, change1);
// rinse, repeat for other colors
You may need to play with the tolerance for the AvoidXfermode, but that should do what you want a lot faster than a per-pixel calculation. Also, make sure your chart image is in ARGB8888 mode. By default, Android tends to work with images in RGB565 mode, which tends to mess up color calculations like you want to use - to be sure, you can make sure your image is both in ARGB8888 mode and mutable by calling Bitmap chart = chartFromServer.copy(Config.ARGB_8888, true); before you setup the Xfermode.
Clarification: to change other colors, you wouldn't have to re-load the images all over again, you would just have to create other Paints with the appropriate colors you want changed like so:
// changes green to red
Paint change1 = new Paint();
change1.setColor(Color.GREEN);
change1.setXfermode(new AvoidXfermode(Color.RED, 245, AvoidXfermode.Mode.TARGET));
// changes white to blue
Paint change2 = new Paint();
change2.setColor(Color.BLUE);
change2.setXfermode(new AvoidXfermode(Color.WHITE, 245, AvoidXfermode.Mode.TARGET));
// ... other Paints with other changes you want to apply to this image
Canvas c = new Canvas();
c.setBitmap(chart);
c.drawRect(0, 0, width, height, change1);
c.drawRect(0, 0, width, height, change2);
//...
c.drawRect(0, 0, width, height, changeN);