Java: save grayscale int array to image

Question

I currently have a simple int[] array of grayscale values from 0 ... 255. I want to save the values to a simple image file. I do the following:

// flatten the 2d array
int[] result = Arrays.stream(imgData)
    .flatMapToInt(Arrays::stream)
    .toArray();

BufferedImage outputImage = new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
outputImage.setRGB(0, 0, w, h, result, 0, w);
ImageIO.write(outputImage, INPUT_FILETYPE, new File(getOutputFileSystemString()));

This actually works fine, but the image is very dark, darker than it should be in my opinion.

Here is the outcoming image in IrfanView. You can actually see details, it's not all black, but it is extremely dark. I set every prixel in the upper left corner to 255, but it still is extremely dark, but you can atleast see the outlines which should in my opinion be white:

Does anyone know why?

@ManoDestra Yes. It contains int values from 0 to 255 and is exactly of size int[1024][1024]. — luuksen
– luuksen, Commented Jun 1, 2016 at 15:39
You create an array called result but then you use source in the function call — 001
– 001, Commented Jun 1, 2016 at 15:41
Ah yes, that's actually a copy error on my part as I was testing to put the original greyscale image into the array, but the result was still the same. very dark...it should be result, i edited that. — luuksen
– luuksen, Commented Jun 1, 2016 at 15:44
If you're on Java 8, then you may wish to take a look at the ColorAdjust class. — ManoDestra
– ManoDestra, Commented Jun 1, 2016 at 16:16

ManoDestra · Accepted Answer · 2016-06-01 16:14:47Z

3

I believe you will have better luck using a WritableRaster:

BufferedImage outputImage = new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
WritableRaster raster = outputImage.getRaster();
raster.setSamples(0, 0, w, h, 0, result);
ImageIO.write(outputImage, INPUT_FILETYPE, new File(getOutputFileSystemString()));

edited Jun 1, 2016 at 16:14

ManoDestra

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answered Jun 1, 2016 at 15:46

001

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FiReTiTi · Accepted Answer · 2016-06-05 06:15:23Z

2

You can use the WritableRaster (and forget about getRGB, it's the worst way to access pixels):

int[] myarray = ...
WritableRaster wr = image.getRaster() ;
for (int y=0, nb=0 ; y < image.getHeight() ; y++)
    for (int x=0 ; x < image.getWidth() ; x++, nb++)
        wr.setSample(x, y, 0, myarray[nb]) ;

It's faster to use the DataBuffer, but then you have to handle the image encoding.

edited Jun 5, 2016 at 6:15

answered Jun 1, 2016 at 15:49

FiReTiTi

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