Going from 565 to ARGB 8888 is not what you want. Whenever an image with no alpha channel is decoded, Android (currently) converts it to 565 because this is how it will be rendered on screen. Doing the conversion at drawing time would be a waste of CPU.
What you need is to decode the image directly in ARGB 8888. When you call one of the BitmapFactory.decode*() methods, you can specify a set of BitmapFactory.Options. Simply pass a set of options in which inDither == false. This will tell BitmapFactory to not attempt to dither the original 24 bits image to 16 bits. On Sun, Mar 15, 2009 at 7:26 PM, Gavin Aiken <[email protected]> wrote: > 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 > > > > > > > > > -- Romain Guy Android framework engineer [email protected] Note: please don't send private questions to me, as I don't have time to provide private support. All such questions should be posted on public forums, where I and others can see and answer them --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -~----------~----~----~----~------~----~------~--~---
