Detecting if a PNG image file is a Transparent image?

Question

I am looking for a way to quickly determine if a PNG image has transparent features. That is, whether any portion of the image is translucent or displays the background in a

Answer 1

Here is an effective approach: Open the PNG in binary. Seek to byte 26 (25 if counting from zero). Evaluate the byte value of the char: 2 or lower => definitely opaque, 3 or higher => supports transparency. According to my findings, files generated by Photoshop only use 3 or higher when needed making this a reliable way to tell when using these. It appears that almost all of the files have 2 for opaque and 6 for alpha-blended. You may also consider checking the PNG and IHDR strings found in that general area to fool-proof your code.