I am looking for a way to quickly determine if a PNG image has transparent features. Does anyone one know a simple way to detect this?
UPDATE: OK, is there a less complicated way then to pull out the PNG specification and hacking code?
+3
A:
Why not just loop through all of the pixels in the image and check their alpha values?
bool ContainsTransparent(Bitmap image)
{
for (int y = 0; y < image.Height; ++y)
{
for (int x = 0; x < image.Width; ++x)
{
if (image.GetPixel(x, y).A != 255)
{
return true;
}
}
}
return false;
}
APShredder
2010-04-03 02:02:54
Keep in mind that using GetPixel is atrociously slow. You should use the Bitmap.LockBits method to get a pointer to the image data, and use unsafe code to process the image. The GetPixel method will lock the image bits, get the pixel data, build a Color struct, then unlock the image bits every time it is called, requiring orders of magnitude more processing time.
jrista
2010-04-03 02:34:40
I was hoping for something a little quicker than checking every pixel. But it is certainly easier than RTM. I'll have to decide if I have the time for that brute force check. Thanks.
kenny
2010-04-03 10:45:59
It would be more efficient to return true from within the loop, therefore exiting immediately if the first pixel is transparent.
apathetic
2010-07-02 10:09:25
Good idea, I've edited my post accordingly.
APShredder
2010-07-02 14:18:09
+1
A:
Well, i still don't understand the question completely, but if you just want to check, whether a given image may use transparency features, you can use this code:
Image img = Image.FromFile ( "...", true );
if ( (img.Flags & 0x2) != 0)
{
}
Though it won't help you to determine whether a given png file actually uses transparent features, it will indicate, that it has color type 4 or 6 (both support transparency) according to png file specification.
n535
2010-04-03 07:38:02
Thanks, but this isn't helpful for me, since I need to know if the image contained is actually translucent not if it could be. The other answer above works, but I was hoping for something quicker, which this clearly is....
kenny
2010-04-03 10:49:47
This is quite useful. I have used it in combination with the code above so I only inspect the pixels of images that support transparency.
apathetic
2010-07-02 12:25:10