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concat image file not able to create

I try to join two images. But not able to create it.
I am not able to understand what is the problem in the below code.
It is not able to create the concat.jpg file.
BufferedImage image = ImageIO.read(mainFile);
BufferedImage image1 = ImageIO.read(fileToMerge);
int width = Math.max(image.getWidth() , image1.getWidth());
int height = Math.max(image.getHeight() , image1.getHeight());
log.info("width {}", width);
log.info("height {}", height);
BufferedImage concatImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
Graphics2D graphics2D = concatImage.createGraphics();
graphics2D.drawImage(image, 0, image.getHeight(), null);
graphics2D.drawImage(image1, 0 , image1.getHeight(), null);
ImageIO.write(concatImage, "jpg", new File(Constants.LOCAL_FOLDER + "/concat.jpg"));

You want the height of concatImage to be the combined height of image and image1.
You want to draw image at coordinates (0,0) and you want to draw image1 at x = 0 and y = height of image
Try the following.
BufferedImage image = ImageIO.read(mainFile);
BufferedImage image1 = ImageIO.read(fileToMerge);
int width = Math.max(image.getWidth() , image1.getWidth());
int height = image.getHeight() + image1.getHeight();
log.info("width {}", width);
log.info("height {}", height);
BufferedImage concatImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
Graphics2D graphics2D = concatImage.createGraphics();
graphics2D.drawImage(image, 0, 0, null);
graphics2D.drawImage(image1, 0, image.getHeight(), null);
ImageIO.write(concatImage, "jpg", new File(Constants.LOCAL_FOLDER + "/concat.jpg"));
Note that you should call graphics2D.dispose() when you no longer need to use it.

Rotate BufferedImage with transparent background

I have an image with transparent background. I'd like to rotate this image to a specific angle and keep the transparent background for the resulting image. For this purpose I use the following method:
public static BufferedImage rotateImage(BufferedImage image, double angle, Color backgroundColor) {
System.out.println(image.getType());
double theta = Math.toRadians(angle);
double sin = Math.abs(Math.sin(theta));
double cos = Math.abs(Math.cos(theta));
int w = image.getWidth();
int h = image.getHeight();
int newW = (int) Math.floor(w * cos + h * sin);
int newH = (int) Math.floor(h * cos + w * sin);
BufferedImage tmp = new BufferedImage(newW, newH, image.getType());
Graphics2D g2d = tmp.createGraphics();
if (backgroundColor != null) {
g2d.setColor(backgroundColor);
g2d.fillRect(0, 0, newW, newH);
}
g2d.fillRect(0, 0, newW, newH);
g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);
g2d.translate((newW - w) / 2, (newH - h) / 2);
g2d.rotate(theta, w / 2, h / 2);
g2d.drawImage(image, 0, 0, null);
g2d.dispose();
return tmp;
}
I invoke it with background=null:
BufferedImage image = ImageIO.read(file);
rotateImage(image, 4, null);
ImageIO.write(bi, "PNG", new File("image.png"));
but the background of the resulting image.png is WHITE. What am I doing wrong and how to properly keep the transparent background for image.png?

I'm a bit puzzled about the behavior of Graphics.drawImage(). Maybe somebody else can comment about it.
However, Graphics2D.drawRenderedImage() works a treat. It takes an AffineTransform to control the rotation. The below example nicely works. You probably have additional requirement about the final image size and the location of the rotated image.
import javax.imageio.ImageIO;
import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.File;
public class ImageRotation {
public static void main(String[] args) {
ImageRotation rotation = new ImageRotation();
rotation.rotate("input.png", 45, "output.png");
}
public void rotate(String inputImageFilename, double angle, String outputImageFilename) {
try {
BufferedImage inputImage = ImageIO.read(new File(inputImageFilename));
BufferedImage outputImage = rotateImage(inputImage, angle);
ImageIO.write(outputImage, "PNG", new File(outputImageFilename));
} catch (Exception e) {
throw new RuntimeException(e);
}
}
private BufferedImage rotateImage(BufferedImage sourceImage, double angle) {
int width = sourceImage.getWidth();
int height = sourceImage.getHeight();
BufferedImage destImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
Graphics2D g2d = destImage.createGraphics();
AffineTransform transform = new AffineTransform();
transform.rotate(angle / 180 * Math.PI, width / 2 , height / 2);
g2d.drawRenderedImage(sourceImage, transform);
g2d.dispose();
return destImage;
}
}
Update
While the above code works for most PNGs, it does not work for the image that alexanoid is using. I've analyzed the image:
It's a grayscale image without a color palette (PNG color type 0) .
It uses simple transparency with a 2 byte long tRNS chunk.
As far as I can tell that's perfectly legal. However, ImageIO does not implement this combination. If the image has no palette, it simply ignores the tRNS chunk and therefore ignores the transparency information. That's most likely a bug.
You basically have two options now:
Look for an alternative library to read PNG files.
Fix the transparency after you have read the PNG file. This only works if know that the image used the particular problematic format.
Input and output for working PNG files
Input image:
Ouptput Image:

Reshape a bufferedImage and store the double values in txt

I want to load an image to resize it to 100x100 to reshape it in 1x100000 and save it in an txt file. So I read it in bufferedImage, I resize it to 100x100. The next steps for reshaping it and save the double values of it is what I am looking for:
File img = new File(train_path + fileNames.get(i) + "/" + imageNames.get(i).get(j));
BufferedImage in = ImageIO.read(img);
BufferedImage newImage = new BufferedImage(in.getWidth(), in.getHeight(), BufferedImage.TYPE_BYTE_GRAY);
Graphics2D g = newImage.createGraphics();
g.drawImage(in, 0, 0, null);
g.dispose();
BufferedImage newImg = new BufferedImage(100, 100, BufferedImage.TYPE_BYTE_GRAY);
Graphics gr = newImg.createGraphics();
gr.drawImage(newImage, 0, 0, 100, 100, null);
gr.dispose();
System.out.println(newImage.getHeight()+ " "+ newImage.getWidth());
System.out.println(newImg.getHeight()+ " "+ newImg.getWidth());

You can get an array of int from the initial image:
int[] pixels = newImage.getRGB(0, 0, 100, 100, null, 0, 100);
which means get RGB values from (0,0) to (100,100) in a new array, starting from index 0, offsetting index for each line of 100.
Then for each int in pixels, the grayscale value is given by:
int gray = pixels[i] & 0xFF;

Black Padding with images in java?

I have this problem. I am using this code to rotate an image but the rotated image has black padding in its corners due to rotation.
How could I remove it?
public static BufferedImage rotate(BufferedImage img, int angle) {
rotate_checked = false;
int w = img.getWidth();
int h = img.getHeight();
BufferedImage dimg =new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
Graphics2D g = dimg.createGraphics();
g.rotate(Math.toRadians(angle), w/2, h/2);
g.drawImage(img, null, 0, 0);
return dimg;
}

You need to create a transparent image:
BufferedImage buffer = gc.createCompatibleImage(height, width, Transparency.TRANSLUCENT);
where 'gc' is a Graphics2D object. You can also create one directly with new BufferedImage() of course, but this will give you the most efficient-to-use image for your particular graphics context.

Java BufferedImage padding

Is there any faster way to achieve padding of pixels to a BufferedImage than drawing it centered on larger BufferedImage?

BufferedImage has a constructor where you get to specify a WriteableRaster.
Picking at the a default buffered image, storing each pixel in an int, it uses an IntegerInterleavedRaster.
The ColorModel you can use ColorModel.getRGBDefault().
int imageWidth = 638, imageHeight = 480;
int dataImageWidth = 640;
SampleModel sm = new SinglePixelPackedSampleModel(TYPE_INT, imageWidth, imageHeight, dataImageWidth, new int[] { 0xff0000, 0xff00, 0xff });
DataBuffer db = new DataBufferInt(dataImageWidth * imageHeight);
WritableRaster r = Raster.createWritableRaster(sm, db, new Point());
BufferedImage image = new BufferedImage(ColorModel.getRGBDefault(), r, false, null);
Notice the scanlineStride in SinglePixelPackedSampleModel (second last parameter).
Another much simpler approach is to use BufferedImage's getSubimage method.
BufferedImage fullImage = new BufferedImage(dataImageWidth, imageHeight);
BufferedImage subImage = fullImage.getSubimage(0, 0, imageWidth, imageHeight);

Create an ImageIcon using the BufferedImage and add the Icon to a JLabel. Then you can just add a Border to the label to get your desired padding.

To defer centering until rendering, I like this approach due to finnw, where this is a suitable component:
private BufferedImage image;
....
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.translate(this.getWidth() / 2, this.getHeight() / 2);
g2d.translate(-image.getWidth() / 2, -image.getHeight() / 2);
g2d.drawImage(image, 0, 0, null);
}