iOS Find the alpha value

[iphonejudy]

I saw a document find a alpha value like below,

return pixelData[y * width + x]/255;

But i got error ,Invalid operands to binary /

 

[admanimal]

It is impossible to tell what is going on with the amount of code you gave, but chances are that pixelData is a char array that holds the raw binary image data...and I'm guessing that you're not actually working with the same type of variable in your own objective-c code.

 

[iphonejudy]

I saw a hasalpha mehod to find the alpha value.But it finds the alpha value only for image.

Its a great drawback that iphone doesnot have a method to find the alpha value for a pixel