默认关闭背景

tests/pma-color-rendering.html

@@ -10,7 +10,7 @@
  // Produce a PNG whose low-alpha RGB values can be represented exactly by
  // Canvas's 8-bit storage; PMA consumers must preserve those encoded values.
  const encoded=canvas(),pixels=encoded.createImageData(32,32);
- for(let i=0;i<pixels.data.length;i+=4)pixels.data.set([64,32,16,8],i);
+ for(let i=0;i<pixels.data.length;i+=4)pixels.data.set([16,8,0,32],i);
  encoded.putImageData(pixels,0,0);
  const blob=await new Promise(resolve=>encoded.canvas.toBlob(resolve));
  const image=new Image();image.src=URL.createObjectURL(blob);await image.decode();