How to tell if PNG file has an Alpha Channel / Transparency

Question

Trying to find the best / easiest way using Objective C on MAC OSX if a PNG file has an Alpha Channel.

score 1 · Accepted Answer · answered Jul 08 '15 at 17:06

1

Here's one way:

NSBitmapImageRep *rep = [NSBitmapImageRep imageRepWithContentsOfFile:@"/path/to/image/test.png"];
BOOL alpha = [rep hasAlpha];

answered Jul 08 '15 at 17:06

Doug Lowder

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Very nicely done. I am an iOS guy and I looked for something like this but could not find. Thanks Again.... – ort11 Jul 09 '15 at 00:00

score 0 · Answer 2 · answered Jul 07 '15 at 17:51

0

If the color-type byte, which is at a known location within the IHDR chunk, is 0, 2, or 3 AND there is no tRNS chunk present before the first IDAT chunk, there is no alpha channel and the image is opaque. If a tRNS chunk is present, or if the color-type is 4 or 6, the image has an alpha channel, which might have transparency in some pixels or it might be opaque.

answered Jul 07 '15 at 17:51

Glenn Randers-Pehrson

11,940
3
37
61

Thanks, was researching this. Was wondering if there was an API like in iOS with CGImage that has an api for YES or NO. – ort11 Jul 07 '15 at 21:33

How to tell if PNG file has an Alpha Channel / Transparency

2 Answers2