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Java: change alpha of BufferedImage with a polygon

I have a buffered image which has a set alpha and would like to change the alpha of the buffered image but only in a specific polygon.
For example the buffered image has an alpha of 200 and i want to add 20 to all the pixels on the buffered image within(or colliding with) the polygon.
I couldn't find any which does this exactly in the graphics class or on Google.
I would appreciate any form of help :D
Thanks!

JAI Add Alpha Channel to RenderedImage

I have two RenderedImages. I want to do an Overlay Operation with these two images and therefore they need to match in data type and the number of bands.
The problem I have is that one image has 3 bands (RGB) and the second image has 4 bands (ARGB).
My question is how can I add an Alpha Channel to the first image so I can do the Overlay Operation?
EDIT
Ok, I found a method of adding an Alpha Channel to the first image. Below is the code. I simply created a single banded constant image and merged it with my first image.
ParameterBlock pb = new ParameterBlock();
pb.add(new Float(finalImage.getWidth())).add(new Float(finalImage.getHeight()));
pb.add(new Byte[] {new Byte((byte)0xFF)});
RenderedImage alpha = JAI.create("constant", pb);
finalImage = BandMergeDescriptor.create(finalImage, alpha, null);
The problem I have now is that everytime I add an overlay the image changes colors. All the colors become nuances of red or pink. When I add a second overlay, the image becomes normal again, but the first overlay changes colors. All black areas become white.
Also the background of the overlay is not transparent. It is grey.
Below are examples of the images, so you see how the change colors:
As you can see, the picture and overlays change colors and the background of the overlay isn't transparent.
Can you help me solve this problem, so that the image is always displayed correctly? Thanks!

You can try to create a new BufferedImage with ARGB-model, and just paint the non-transparent background picture into this new BufferedImage. Then you have a BufferedImage with alpha-channel (although all of the pixels are opaque), so the Composition should hopefully work.

im not sure about TYPE_4BYTE_ARGB as I usually work with BufferedImages of TYPE_INT_ARGB but I have often used the method of drawing a RGB BufferedImage to a new ARGB BufferedImage and then drawing that onto other things without problem. the change in color would suggest an unwanted change is being made to the other channels in the overlay process as it doesn't seem to be specific to a specific image. If your overlay operation is similar to drawing one image onto another with alpha I would probably suggest using the Graphics.drawImage()/drawRenderedImage() method for the overlay itself not to mention the background should not even need alpha in this case.
the code:
public RenderedImage overlay(RenderedImage back, RenderedImage front, AffineTransform overlayTransformation)
{
BufferedImage newBack = new BufferedImage(back.getWidth(), back.getHeight(), TYPE_3BYTE_RGB);
newBack.setData(back.getData());
Graphics2D graphics = (Graphics2D)(newBack.getGraphics());
graphics.drawRenderedImage(front, overlayTransformation);
return newBack;
}
you may want to ensure the original back Raster is not modified though.

Create a Dicom image

I am currently working with a DICOM project in java. I am calculating the dicom values such as depth, off-axis ratio, width and height. I want to create a sample image with the calculated width and height. I should be a gray scale image, with varying densities of gray color in appropriate area. I have created a sample image with imagemagick, using concentric circles. Bit am not getting the exact image. It does not look like an actual dicom image. The variation of gray color does not have a linear behavior. Sample image is attached. Please suggest any other method to create dicom image. The density values are available in a list. depending upon the distance from the center, the gray color also changes according to the density value provided.

Pixel Data or image in DICOM data set is always rectangular and image is described using Rows (0028, 0010) and Columns (0028, 0011) attributes. So the best way to implement this is to draw your circular image on a rectangular background. Fill the background with a color that is not present in your image. Use the Pixel Padding Value (0028,0120) to specify the color used to pad grayscale images (those with a Photometric Interpretation of MONOCHROME1 or MONOCHROME2) to rectangular format.
If you do not have any color to spare (with-in the bit stored), you can add Overlay Plane or Display Shutter to the data set to mask the area that is not part of image.

How to inset a image into a background and save it in JAVA?

I want to inset a image into a background and save it, both are png files with transparency, below code work fine but new image become black & white only.
BufferedImage BUFFEREDIMAGE1=ImageIO.read(new File(strPATH+"/IMAGE.png"));
BufferedImage BUFFEREDIMAGE2=ImageIO.read(new File(strPATH+"/WATERMARK.png"));
Graphics2D GRAPHICS1=BUFFEREDIMAGE1.createGraphics();
GRAPHICS1.drawImage(BUFFEREDIMAGE2,intLeft,intTop,intWidth,intHeight,null);
GRAPHICS1.dispose();
ImageIO.write(BUFFEREDIMAGE2,"png",new File(strPATH,"SAVED.png"));

The most likely cause is that at some point the colour space of the image is becoming changed. You may be better off explicitly creating a new destination BufferedImage with the RGB or RGBA format and writing both source Images into it. This removes any possible variation in that area.

create bitmap with alpha from multiple drawables

I am drawing multiple resources onto a bitmap via a canvas. I would like the end result of the composite image to have a certain alpha. Right now I'm setting paint's alpha to the level i want and then drawing each bitmap with that alpha, but i know this would create a composite image of a lot of different alphas. Is there a way to apply an alpha to the entire composite image in performance friendly manner?

You could draw all the drawables fully opaque (alpha = 255) to begin with, then draw over the entire destination Bitmap using Porter-Duff MULTIPLY mode with the right source alpha to change it all at one shot.