如何在Android中显示HDR图片？

Question

I'm doing an android app to decompress, decode and display HDR pictures.
These HDR pictures use 2 bytes per component (A,R,G,B) so one pixel is represented by a 8 bytes value that can only fit with the long type.

I'm using android's Bitmap to display picture as they have a constructor allowing to do HDR by using Bitmap.Config.RGBA_F16 :

int width = 1;
int height = 1;
Bitmap image = Bitmap.createBitmap(width, height, Bitmap.Config.RGBA_F16);

Unfortunately I can't find any way to fill a pixel of the Bitmap. I use the recommended formula but it cannot be used in the setPixel(x,y,color) method of Bitmap because color has to be a int:

long color = (A & 0xffff) << 48 | (B & 0xffff) << 32 | (G & 0xffff) << 16 | (R & 0xffff);
image.setPixel(0,0,color); //Argument type error

.
I have also tried with Color ( which has a HDR compatible method ), Paint and Canvas but no Bitmap method accepts them to set only one pixel.

Thanks for any help!

Answer 1

If you need to open an HDR file, such as 16-bit png, and then display it, you can use ImageDecoder.setTargetColorSpace to create bitmap with format Bitmap.Config.RGBA_F16 like so:

File file = new File(...);
ImageDecoder.Source source = ImageDecoder.createSource(file);
Drawable drawable = ImageDecoder.decodeDrawable(source, (decoder, info, src) -> {
    decoder.setTargetColorSpace(ColorSpace.Named.EXTENDED_SRGB);
});

If you need to display HDR image that is stored in memory you can use Bitmap.copyPixelsFromBuffer , as this method allows to set pixels of the bitmap without conversion of color space the way Bitmap.setPixel does. In this case you need to pack 4 channels represented byHalf values into long for each pixel, then write these long values into a Buffer and finally copy pixels from the buffer to the bitmap.

LongBuffer buffer = LongBuffer.allocate(width * height);
for (int y = 0; y < height; y++) {
    for (int x = 0; x < width; x++) {
        // fill pixels values as needed
        float r = (float)y / height;
        float g = (float)y / height;
        float b = (float)y / height;
        float a = 1f;
        long rBits = Half.halfToShortBits(Half.toHalf(r));
        long gBits = Half.halfToShortBits(Half.toHalf(g));
        long bBits = Half.halfToShortBits(Half.toHalf(b));
        long aBits = Half.halfToShortBits(Half.toHalf(a));
        long color = aBits << 48 | bBits << 32 | gBits << 16 | rBits;
        buffer.put(color);
    }
}
buffer.rewind();

bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGBA_F16);
bitmap.copyPixelsFromBuffer(buffer);