读取 EXIF 并确定闪光灯是否已闪光

Question

我一直在用 PHP 脚本读取一些 EXIF 数据。我想确定某个图像是否使用了闪光灯。以下是 EXIF 读取器返回的值，

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

其中哪些值表示 Flash 已被使用？

此致， 姆拉乔

Answer 1

flash 属性实际上是以下标志的组合：

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

要检查 flash 是否已闪光，请将 flash 属性与 1 按位与：

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

Answer 2

我相信，如果将十六进制值转换为二进制，最右边的数字将指示闪光灯是否实际闪光。

因此：

状态	十六	进制二进制	已触发
无闪烁	0x0	00000000	无
触发	0x1	00000001	是
“已触发，未检测到返回”	0x5	00000101	是
“已触发，检测到返回”	0x7	00000111	是
“开启，未触发”	0x8	00001000	否
“已启动，已触发”	0x9	00001001	是
“开，未检测到返回”	0xd	00001011	是
“开，检测到返回”	0xf	00001111	否
“关，未触发”	0x10	00010000	是
“关，未触发，未检测到返回”	0x14	00010100	否
“自动，未检测到火”	0x18	00011000	否
“自动、触发”	0x19	00011001	是
“未检测到自动、触发、返回”	0x1d	00011101	是
“检测到自动、触发、返回”	0x1f	00011111	否
无闪光功能	0x20	00100000	是
“关闭、无闪光功能”	0x30	00110000	否
“已触发，红眼消除”	0x41	01000001	是
“已触发，红眼消除，未检测到返回”	0x45	01000101	是
“已触发，红眼消除，检测到返回”	0x47	01000111	是
“开启，红眼消除”	0x49	01001001	是
“开，红眼减少，未检测到返回”	0x4d	01001101	是
“开启，红眼消除，检测到返回”	0x4f	01001111	是
“关闭，红眼消除”	0x50	01010000	否
“自动，未触发，红眼消除”	0x58	01011000	否
“自动、触发、红眼消除”	0x59	01011001	是
“自动、触发、红眼消除、未检测到返回”	0x5d	01011101	是
“自动、触发、红眼消除、检测到返回”	0x5f	01011111	是

Answer 3

为了简化问题，您可以遵循以下原则：奇数值表示闪光灯已闪光，偶数值（包括零）表示闪光灯未闪光。

您可以在 Tiff 标签参考中获取更多信息和每个值的含义。

Answer 4

为什么要检查大量列表？对于照片文件，通常只对发生的事件感兴趣，而不是相机的前一个（可能不活动）开关位置！因此，只需进行一些二进制比较即可查询有效的闪光事件（请参见下面的代码片段）。玩得开心！

    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)"