CODEWITHSUNDEEP
javabufferedimagejavax.imageiobmp
Harald K
Harald K

Reputation: 27074

Writing a BMP with transparency using ImageIO

Does anyone have a way of storing a BufferedImage with transparency as BMP in Java? Preferably using the ImageIO API.

For some reason I can't write a BMP in ARGB (BGRA) format, even though the BMP has supported alpha channel since, at least, Win95. I can, however, easily write the same image as a PNG. It also works fine storing an image without alpha, like TYPE_INT_RGB or TYPE_3BYTE_BGR.

Consider the following code snippet:

public static void main(String[] args) throws IOException {
    if (!ImageIO.write(new BufferedImage(300, 200, BufferedImage.TYPE_INT_ARGB), "BMP", new File("foo.bmp"))) {
        System.err.println("Couldn't write BMP!");
    }
    if (!ImageIO.write(new BufferedImage(300, 200, BufferedImage.TYPE_INT_ARGB), "PNG", new File("foo.png"))) {
        System.err.println("Couldn't write PNG!");
    }
}

Output:

Couldn't write BMP!

Upvotes: 1

Views: 680

Answers (1)

Mark Jeronimus
Mark Jeronimus

Reputation: 9543

In BMPImageWriterSpi:

public boolean canEncodeImage(ImageTypeSpecifier type) {
    ...
    if (!(numBands == 1 || numBands == 3))
        return false;

I'm afraid Java doesn't support 32 bit BMPs. You'd have to write your own or find an existing library (ImageJ comes to mind although I don't know if it supports BMP). Wikipedia is very elaborate on the file format and it looks quite easy, even giving a complete field-by-field example of a 32-bit BMP.

Upvotes: 2

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