Creating image from float array, index out of bounds

Question

Why would this method throw an index out of bounds error? Trying to create an image from data I generate myself and I expected this would work.

private BufferedImage getImageFromFloatArray(float[] data, int w, int h) {
    BufferedImage img = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
    System.out.println("Image pixel array size: "
                    + ((DataBufferInt) img.getRaster().getDataBuffer())
                            .getData().length);
    System.out.println("Datasize: " + data.length);
    WritableRaster raster = img.getRaster();
    raster.setPixels(0, 0, w, h, data);
    return img;
}

Stacktrace

Image pixel array size: 800000
Datasize: 800000
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 800000
    at java.awt.image.SampleModel.setPixels(Unknown Source)
    at java.awt.image.WritableRaster.setPixels(Unknown Source)
    at image.PixelAraryToImageTest.getImageFromFloatArray(PixelAraryToImageTest.java:36)

Arent you using threads ? There cound be possibility then, that you change data array. — Martin Perry
– Martin Perry, Commented Jul 30, 2013 at 19:50
No I am afraid it is singlethreaded, the testcase just generates a random data array and tries to create an image. — arynaq
– arynaq, Commented Jul 30, 2013 at 19:53
Is it an ignorant question to ask why you are storing floats into an INT_ARGB type buffer? — Jongware
– Jongware, Commented Jul 30, 2013 at 19:58
@Jongware Float is 4byte data type, so does ARGB. If you want to "visualise" float data as image, you dotn have any other choice. — Martin Perry
– Martin Perry, Commented Jul 30, 2013 at 20:01
I've solved this in my answer below. Thanks @arynaq for your post, this was interesting. — William Morrison
– William Morrison, Commented Jul 30, 2013 at 20:11

William Morrison · Accepted Answer · 2013-07-30 20:16:00Z

1

Try using the Raster width and height variables instead of the BufferedImage width and height variable. Also use Raster.getMinX() and Raster.getMinY()

Every value in the float array isn't a pixel value. Every value is a color component value. So a 2x1 image would actually need to be of length 4, as you have ARGB color components. To make it a 2x1 image red for example, would require something like...

int numColorComponents = 4;
float[] data = new float[imgWidth*imgHeight*numColorComponents];
raster.setPixels(minX,minY, rasterWidth,rasterHeight, data);

Also, unlike other graphics frameworks, the float buffer here isn't a buffer of normalized values. Its value between [0, 255]. So, to set 2x1 image to opaque red, your buffer would be:

float alpha = 255;
float red = 255;   
float[] buffer = new float[]{alpha,red,0,0,alpha,red,0,0};

edited Jul 30, 2013 at 20:16

answered Jul 30, 2013 at 19:51

William Morrison

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1 Comment

arynaq Over a year ago

Ah yes this makes sense, I will have to decompose each sample into four components, will post update.

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