java - ImageIO.write bmp does not work

Question

I'm trying to save an image in bmp format, but it doesn't create any file. If I use "png" instead, everything works fine. Any ideas?

//This works fine:
ImageIO.write(bi, "png", new File("D:\MyImage.png"));

//This does not work:
ImageIO.write(bi, "bmp", new File("D:\MyImage.bmp"));

ImageIO.getWriterFormatNames() gives me "jpg", "bmp", "jpeg" and some others..

Thanks in advance.

Jakob

Answer 1

I just finished debugging a similar problem and I thought I will present my reasoning here, although Jakob has gone ahead with the PNG format.

First, always check the return value of ImageIO.write(...). It will return false if no appropriate writer can be found and that's what should have happened when Jakob tried writing it as a bitmap. This happens when the actual image format of the file does not match what is given in the 'format name' argument. No exception is thrown in this case. Check out the docs at http://docs.oracle.com/javase/7/docs/api/javax/imageio/ImageIO.html#write(java.awt.image.RenderedImage, java.lang.String, java.io.File)

Second, check the image type of the BufferedImage object by using the BufferedImage#getType() method. Check out the possible return values at http://docs.oracle.com/javase/7/docs/api/java/awt/image/BufferedImage.html#getType(). For example, If you get the type as TYPE_INT_ARGB from your BufferedImage object (which represents a PNG with a alpha component) you wont have success using ImageIO.write(bi, "BMP", new File("D:\test.bmp")) and the method would return false, even though you can see BMP/bmp in the list of entries obtained using ImageIO.getWriterFormatNames(). You might have to work on the encoding and transform your image to the desired format.

Third, when facing such problems which can be a pain sometimes, it always helps to use an image editor such as GIMP to check out your image properties in detail.

@Green arrow, a minor note... you can use either "bmp" or "BMP" as the image format value. The same applies for other formats as well. It does not matter.