Sprite color distortion --- how do I disable Premultiplied?

[UltimateWalrus]

Hello,

 

I am experiencing what I think is a quirk of WebGL's premultiplied rendering.  My *.PNG sprites are getting rendered with slightly different RGB values than in the source file.  However, a *.BMP sprite renders with perfect color, which supports my hypothesis that WebGL's premultiplied alpha is to blame.

Basically, I just want to know how to disable premultiplied alpha for a texture in PIXI.

Here is a screenshot (pull it up in Photoshop and sample the colors if you don't believe me):

 

:

Here is my source:

    var renderer = PIXI.autoDetectRenderer(800, 600,{backgroundColor : 0x1099bb});    document.body.appendChild(renderer.view);    // create the root of the scene graph    var stage = new PIXI.Container();    //Create a BMP sprite so we know what the colors are supposed to look like    var bmp_spr = PIXI.Sprite.fromImage( 'test.bmp' );    stage.addChild(bmp_spr);    //Create a PNG sprite to demonstrate the distorted colors    var png_spr = PIXI.Sprite.fromImage( 'test.png' );    png_spr.position.x = 64;    stage.addChild(png_spr);    //Try to create a non-premultiplied PNG sprite to fix the problem    var base_tex = PIXI.BaseTexture.fromImage( 'test2.png' );    base_tex.premultipliedAlpha = false;    var tex = new PIXI.Texture( base_tex );    var nomult_spr = new PIXI.Sprite( tex );    nomult_spr.x = 128;    stage.addChild( nomult_spr );    // start animating    animate();    function animate()    {        requestAnimationFrame(animate);        // render the container        renderer.render(stage);    }

Test images are attached.

 

Normally I'd be all for the speed boost that comes from premultiplying alpha, but it's ruining a shader I'm trying to write, where the tiny color differences butterfly effect out into huge glitches. 

 

I tried to disable premultiplied alpha in the source above but it didn't correct the colors, all it did was disable transparency.

Thanks for any help!
---Sebastian
 

test.bmp