Read EXIF and determine if the flash has fired

Question

I have been reading some EXIF data with my PHP script. I want to determine for a certain image if the flash has been used. Here are the values returned by EXIF reader

0x0     = No Flash
0x1     = Fired
0x5     = Fired, Return not detected
0x7     = Fired, Return detected
0x8     = On, Did not fire
0x9     = On, Fired
0xd     = On, Return not detected
0xf     = On, Return detected
0x10    = Off, Did not fire
0x14    = Off, Did not fire, Return not detected
0x18    = Auto, Did not fire
0x19    = Auto, Fired
0x1d    = Auto, Fired, Return not detected
0x1f    = Auto, Fired, Return detected
0x20    = No flash function
0x30    = Off, No flash function
0x41    = Fired, Red-eye reduction
0x45    = Fired, Red-eye reduction, Return not detected
0x47    = Fired, Red-eye reduction, Return detected
0x49    = On, Red-eye reduction
0x4d    = On, Red-eye reduction, Return not detected
0x4f    = On, Red-eye reduction, Return detected
0x50    = Off, Red-eye reduction
0x58    = Auto, Did not fire, Red-eye reduction
0x59    = Auto, Fired, Red-eye reduction
0x5d    = Auto, Fired, Red-eye reduction, Return not detected
0x5f    = Auto, Fired, Red-eye reduction, Return detected

Which of them mean that the flash has been used?

Best regards, Mladjo

Answer 1

I believe if you convert the hex value to binary, the right-most digit then indicates if the flash actually fired or not.

Therefore:

Status	Hex	Binary	Fired
No Flash	0x0	00000000	No
Fired	0x1	00000001	Yes
"Fired, Return not detected"	0x5	00000101	Yes
"Fired, Return detected"	0x7	00000111	Yes
"On, Did not fire"	0x8	00001000	No
"On, Fired"	0x9	00001001	Yes
"On, Return not detected"	0xd	00001011	Yes
"On, Return detected"	0xf	00001111	Yes
"Off, Did not fire"	0x10	00010000	No
"Off, Did not fire, Return not detected"	0x14	00010100	No
"Auto, Did not fire"	0x18	00011000	No
"Auto, Fired"	0x19	00011001	Yes
"Auto, Fired, Return not detected"	0x1d	00011101	Yes
"Auto, Fired, Return detected"	0x1f	00011111	Yes
No flash function	0x20	00100000	No
"Off, No flash function"	0x30	00110000	No
"Fired, Red-eye reduction"	0x41	01000001	Yes
"Fired, Red-eye reduction, Return not detected"	0x45	01000101	Yes
"Fired, Red-eye reduction, Return detected"	0x47	01000111	Yes
"On, Red-eye reduction"	0x49	01001001	Yes
"On, Red-eye reduction, Return not detected"	0x4d	01001101	Yes
"On, Red-eye reduction, Return detected"	0x4f	01001111	Yes
"Off, Red-eye reduction"	0x50	01010000	No
"Auto, Did not fire, Red-eye reduction"	0x58	01011000	No
"Auto, Fired, Red-eye reduction"	0x59	01011001	Yes
"Auto, Fired, Red-eye reduction, Return not detected"	0x5d	01011101	Yes
"Auto, Fired, Red-eye reduction, Return detected"	0x5f	01011111	Yes

Answer 2

Why checking huge listings? With photo files, normally only occurrence is of interest, not the former (possibly inactive) switch position of the camera! The effective flash event can therefore be queried with just a few binary comparisons (see code snippet below). Have fun!

    function effectiveFlash($flagval) {
/*
    This function uses just 4 major bit comparisons
    and responds with an easy-to-understand answer.
    However, the code could be even shorter, e.g.
    by returning simple symbols instead of text.
*/
    $result = 'not fired'; // First we assume nothing!
    // 1st check: Bit-1
    if(($flagval & 1) > 0) {
        $result = 'fired';
        // Prepare opening and closing text part for possible subsequent information:
        $sep = ' (Setting: ';
        $end = "";
        // 2nd check: Bit-16 plus possibly enclosed Bit-8
        if (($flagval & 24) > 0) {
            if (($flagval & 24) == 24) $result .= $sep . 'Auto';
            else $result .= $sep . 'Compulsory';
            $sep = ' + ';
            $end = ')';
        }
        // 3rd check: Bit-64
        if(($flagval & 64) > 0) {
            $result .= $sep . 'Red Eye Reduction';
            $sep = ' + ';
            $end = ')';
        }
        // 4th check: Bit-4 plus possibly enclosed Bit-2
        if(($flagval & 6) > 0) {
            if(($flagval & 6) == 6) $result .= $sep . 'Return Light';
            else $result .= $sep . 'No Return Light';
            $sep = ' + ';
            $end = ')';
        }
        // Now add the closing bracket ... that's it!
        $result .= $end;
    }
    return 'Flash ' . $result;
}

// Examples:
echo effectiveFlash(1)."<br>\n";
echo effectiveFlash(16)."<br>\n";
echo effectiveFlash(31)."<br>\n";
echo effectiveFlash(77)."<br>\n";

The Output would be like this:
  "Flash fired"
  "Flash not fired"
  "Flash fired (Setting: Auto + Return Light)"
  "Flash fired (Setting: Compulsory + Red Eye Reduction + No Return Light)"

Answer 3

To simplify things, you can follow this: odd value means flash fired and even value (including zero) means flash did not fire.

You can get more information and meaning of each value at Tiff Tag Reference.

Answer 4

The flash property is actually a combination of the following flags:

0:  FlashDidNotFire
1:  FlashFired
2:  StrobeReturnLightDetected
4:  StrobeReturnLightNotDetected
8:  CompulsoryFlashMode
16: AutoMode
32: NoFlashFunction
64: RedEyeReductionMode

To check if the flash has fired, bitwise AND the flash property with 1:

$flashfired = ($exifflashproperty & 1) != 0;