Hi all!
I am trying to perform a transformation on an image, specifically a PNG
although any lossless format supported by Android would suit me, when
running my test suite I keep getting errors that the new pixel values I'm
creating are slightly wrong.
To narrow the problem I ran my tests with a single pixel PNG image and got
some bizarre results. I started by opening the file with gimp and using the
pippet to grab the argb value (Not very scientific I know) the pixel has the
following properties;
Red: 250
Green: 114
Blue: 142
Hex: 0xFA728E
Binary: 0b11111010 01110010 10001110
To me this suggests the file is stored in 32 bit depth and not the RGB_565
later reported, do images in res/raw get reduced to 16 bit when packaged
with an application?
In my test case I check that the values agree in the preconditions
@SmallTest
public void testPreconditions() {
super.testPreconditions();
assertEquals(String.format("Get Pixel doesn't map to test data
%n%s%n%s%n",MiffedTest.getBitPattern(b.getPixel(0,0)),
MiffedTest.getBitPattern(*0xfffa728e*)),b.getPixel(0,0), 0xfffa728e);
}
I eventually get the following report;
Failure in testPreconditions:
junit.framework.AssertionFailedError: Get Pixel doesn't map to test data
11111111 11110111 01110001 10001100
11111111 11111010 01110010 10001110
expected:<-560756> but was:<-363890>
I decode the single pixel PNG using the following command;
b =
BitmapFactory.decodeResource(getContext().getResources(),R.raw.test);
The config for b is RGB_565 , this worries me, I was using the format in the
hope that it was lossless but 16 bit colour is not a great sign, I feel like
the crux of this issue lies in the conversion from RGB_565 -> ARGB_8888
which much take place in the getPixel method.
Does anyone know why these values are out? They're such minor amounts but
the issues grow the more work I do to an image.
How is the conversion from the RGB_565 format to the 32 bit integer returned
by getPixel done? Some low end bits seem to be set so it's not the method
I'm used to.
Is there any other way to get at the raw pixel data if the methods are
inaccurate?
Is there any way for me to store or convert a PNG in ARGB_8888 on the
platform? I just need to be able to get the exact 32 bit value of any pixel
from the image.
Any information would be greatly appreciated.
Kind regards,
Gav
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