中文(繁體)
中文(繁體)
在PHP 中， image_type_to_extension(int $image_type, bool $include_dot = true): string|false常用於把（如IMAGETYPE_PNG ）轉換為擴展名（如.png ）。
但在真實項目裡，很多同學會反饋它“返回了錯誤的擴展名”。多數情況下並不是函數錯了，而是調用方式或前置判斷有問題。
下面把常見“誤判”源頭、復現方式與修正方案一次講清。
把“文件名/ MIME 字符串/ 文件路徑”錯當成$image_type
image_type_to_extension()需要的是整型常量（ IMAGETYPE_* ），而不是'image/jpeg' 、 'xxx.jpg'或者文件路徑。
錯誤示例： image_type_to_extension('image/jpeg') → 期望返回.jpg ，實際會得到false或報錯。
$image_type取值來源不對
正確做法：用exif_imagetype($file)或getimagesize($file)[2]拿到整型類型值。
錯誤做法：從$_FILES['type'] （客戶端可偽造）或finfo_file()的MIME 字符串直接傳入。
對返回的.jpeg與.jpg期望不一致
規範上JPEG 的擴展名可以是.jpeg或.jpg 。 image_type_to_extension(IMAGETYPE_JPEG)默認返回.jpeg 。
如果你業務裡統一用.jpg ，需要手動做別名轉換。
第二個參數$include_dot理解反了
默認true會返回帶點的擴展名（如.png ）。
你要不帶點： image_type_to_extension($t, false) → png 。
常見情況：你拼接路徑又手動加了一個點，結果變成..png 。
GD/擴展支持與期望格式不匹配
部分類型（如WebP、AVIF）需要相應GD/Imagick 版本支持。雖然image_type_to_extension()能給出擴展名，但後續保存函數（如imagewebp ）可能不存在或不可用，導致你“以為擴展名錯了”，本質是保存環節不支持。
另一些類型如IMAGETYPE_WBMP返回.wbmp ，不少人誤以為是.bmp 。
內容與擴展名不一致（寫入環節用錯函數）
你檢測到是PNG，卻用imagejpeg()保存，硬生生把位圖寫成了JPEG，然後再拿到.png擴展，文件“名實不符”。
反之亦然：請確保檢測結果與保存函數一致。
來自finfo_file()的MIME 到擴展直接映射失真
finfo返回image/jpeg之類的MIME，你若自己做字符串映射，可能把image/jpeg → .jpg ，而image_type_to_extension()會給.jpeg ；看似“錯”，實為映射不一致。
<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-variable">$file</span></span><span> = </span><span><span class="hljs-string">'/path/to/uploaded/file'</span></span><span>;
</span><span><span class="hljs-comment">// 方法 A：更穩</span></span><span>
</span><span><span class="hljs-variable">$type</span></span><span> = @</span><span><span class="hljs-title function_ invoke__">exif_imagetype</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>); </span><span><span class="hljs-comment">// 返回 IMAGETYPE_* 整數或 false</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$type</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
</span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">RuntimeException</span></span><span>(</span><span><span class="hljs-string">'無法識別圖片類型'</span></span><span>);
}
</span><span><span class="hljs-comment">// 方法 B：getimagesize</span></span><span>
</span><span><span class="hljs-variable">$info</span></span><span> = @</span><span><span class="hljs-title function_ invoke__">getimagesize</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>);
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$info</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
</span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">RuntimeException</span></span><span>(</span><span><span class="hljs-string">'不是有效的圖片'</span></span><span>);
}
</span><span><span class="hljs-variable">$type</span></span><span> = </span><span><span class="hljs-variable">$info</span></span><span>[</span><span><span class="hljs-number">2</span></span><span>]; </span><span><span class="hljs-comment">// 同樣是 IMAGETYPE_* 整數</span></span><span>
</span></span>不要把下面這些直接傳給image_type_to_extension() ：
'image/png' （MIME 字符串）
'xxx.jpg' （文件名）
'/path/to/file' （路徑）
很多團隊希望：
JPEG 一律用.jpg （而不是.jpeg ）
去掉點（用於拼接）
增補少見類型的別名
可以封裝一個小函數：
<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">preferred_extension_from_file</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$file</span></span><span>, </span><span><span class="hljs-keyword">bool</span></span><span> </span><span><span class="hljs-variable">$includeDot</span></span><span> = </span><span><span class="hljs-literal">true</span></span><span>): </span><span><span class="hljs-title">string</span></span><span> {
</span><span><span class="hljs-variable">$type</span></span><span> = @</span><span><span class="hljs-title function_ invoke__">exif_imagetype</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>);
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$type</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
</span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">InvalidArgumentException</span></span><span>(</span><span><span class="hljs-string">'無法識別圖片類型：'</span></span><span> . </span><span><span class="hljs-variable">$file</span></span><span>);
}
</span><span><span class="hljs-variable">$ext</span></span><span> = </span><span><span class="hljs-title function_ invoke__">image_type_to_extension</span></span><span>(</span><span><span class="hljs-variable">$type</span></span><span>, </span><span><span class="hljs-variable">$includeDot</span></span><span>);
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$ext</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
</span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">RuntimeException</span></span><span>(</span><span><span class="hljs-string">'無法從類型映射擴展名'</span></span><span>);
}
</span><span><span class="hljs-comment">// 統一大小寫</span></span><span>
</span><span><span class="hljs-variable">$ext</span></span><span> = </span><span><span class="hljs-title function_ invoke__">strtolower</span></span><span>(</span><span><span class="hljs-variable">$ext</span></span><span>);
</span><span><span class="hljs-comment">// 業務偏好別名</span></span><span>
</span><span><span class="hljs-variable">$map</span></span><span> = [
</span><span><span class="hljs-comment">// 只處理你關心的“風格化”差異</span></span><span>
</span><span><span class="hljs-variable">$includeDot</span></span><span> ? </span><span><span class="hljs-string">'.jpeg'</span></span><span> : </span><span><span class="hljs-string">'jpeg'</span></span><span> => </span><span><span class="hljs-variable">$includeDot</span></span><span> ? </span><span><span class="hljs-string">'.jpg'</span></span><span> : </span><span><span class="hljs-string">'jpg'</span></span><span>,
</span><span><span class="hljs-variable">$includeDot</span></span><span> ? </span><span><span class="hljs-string">'.tiff'</span></span><span> : </span><span><span class="hljs-string">'tiff'</span></span><span> => </span><span><span class="hljs-variable">$includeDot</span></span><span> ? </span><span><span class="hljs-string">'.tif'</span></span><span> : </span><span><span class="hljs-string">'tif'</span></span><span>,
];
</span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-variable">$map</span></span><span>[</span><span><span class="hljs-variable">$ext</span></span><span>] ?? </span><span><span class="hljs-variable">$ext</span></span><span>;
}
</span></span>用法：
<span><span><span class="hljs-variable">$ext</span></span><span> = </span><span><span class="hljs-title function_ invoke__">preferred_extension_from_file</span></span><span>(</span><span><span class="hljs-string">'/uploads/a.tmp'</span></span><span>); </span><span><span class="hljs-comment">// 可能返回 .jpg</span></span><span>
</span><span><span class="hljs-variable">$extNoDot</span></span><span> = </span><span><span class="hljs-title function_ invoke__">preferred_extension_from_file</span></span><span>(</span><span><span class="hljs-string">'/uploads/a.tmp'</span></span><span>, </span><span><span class="hljs-literal">false</span></span><span>); </span><span><span class="hljs-comment">// 可能返回 jpg</span></span><span>
</span></span>檢測類型只是第一步，更關鍵的是用正確的寫入函數：
<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">save_image_as_detected</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$srcPath</span></span><span>, </span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$destDir</span></span><span>): </span><span><span class="hljs-title">string</span></span><span> {
</span><span><span class="hljs-variable">$type</span></span><span> = @</span><span><span class="hljs-title function_ invoke__">exif_imagetype</span></span><span>(</span><span><span class="hljs-variable">$srcPath</span></span><span>);
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$type</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
</span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">InvalidArgumentException</span></span><span>(</span><span><span class="hljs-string">'不是有效的圖片：'</span></span><span> . </span><span><span class="hljs-variable">$srcPath</span></span><span>);
}
</span><span><span class="hljs-variable">$ext</span></span><span> = </span><span><span class="hljs-title function_ invoke__">image_type_to_extension</span></span><span>(</span><span><span class="hljs-variable">$type</span></span><span>); </span><span><span class="hljs-comment">// 如 .png / .jpeg / .webp</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$ext</span></span><span> === </span><span><span class="hljs-literal">false</span></span><span>) {
</span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">RuntimeException</span></span><span>(</span><span><span class="hljs-string">'無法映射擴展名'</span></span><span>);
}
</span><span><span class="hljs-comment">// 按類型選擇對應的保存函數</span></span><span>
</span><span><span class="hljs-keyword">switch</span></span><span> (</span><span><span class="hljs-variable">$type</span></span><span>) {
</span><span><span class="hljs-keyword">case</span></span><span> IMAGETYPE_JPEG:
</span><span><span class="hljs-variable">$im</span></span><span> = </span><span><span class="hljs-title function_ invoke__">imagecreatefromjpeg</span></span><span>(</span><span><span class="hljs-variable">$srcPath</span></span><span>);
</span><span><span class="hljs-variable">$filename</span></span><span> = </span><span><span class="hljs-title function_ invoke__">uniqid</span></span><span>(</span><span><span class="hljs-string">'img_'</span></span><span>, </span><span><span class="hljs-literal">true</span></span><span>) . </span><span><span class="hljs-string">'.jpg'</span></span><span>; </span><span><span class="hljs-comment">// 業務偏好：用 .jpg</span></span><span>
</span><span><span class="hljs-title function_ invoke__">imagejpeg</span></span><span>(</span><span><span class="hljs-variable">$im</span></span><span>, </span><span><span class="hljs-variable">$destDir</span></span><span> . </span><span><span class="hljs-string">'/'</span></span><span> . </span><span><span class="hljs-variable">$filename</span></span><span>, </span><span><span class="hljs-number">90</span></span><span>);
</span><span><span class="hljs-keyword">break</span></span><span>;
</span><span><span class="hljs-keyword">case</span></span><span> IMAGETYPE_PNG:
</span><span><span class="hljs-variable">$im</span></span><span> = </span><span><span class="hljs-title function_ invoke__">imagecreatefrompng</span></span><span>(</span><span><span class="hljs-variable">$srcPath</span></span><span>);
</span><span><span class="hljs-variable">$filename</span></span><span> = </span><span><span class="hljs-title function_ invoke__">uniqid</span></span><span>(</span><span><span class="hljs-string">'img_'</span></span><span>, </span><span><span class="hljs-literal">true</span></span><span>) . </span><span><span class="hljs-string">'.png'</span></span><span>;
</span><span><span class="hljs-comment">// 為了小體積：開啟 Alpha，設置壓縮</span></span><span>
</span><span><span class="hljs-title function_ invoke__">imagesavealpha</span></span><span>(</span><span><span class="hljs-variable">$im</span></span><span>, </span><span><span class="hljs-literal">true</span></span><span>);
</span><span><span class="hljs-title function_ invoke__">imagepng</span></span><span>(</span><span><span class="hljs-variable">$im</span></span><span>, </span><span><span class="hljs-variable">$destDir</span></span><span> . </span><span><span class="hljs-string">'/'</span></span><span> . </span><span><span class="hljs-variable">$filename</span></span><span>, </span><span><span class="hljs-number">6</span></span><span>);
</span><span><span class="hljs-keyword">break</span></span><span>;
</span><span><span class="hljs-keyword">case</span></span><span> IMAGETYPE_GIF:
</span><span><span class="hljs-variable">$im</span></span><span> = </span><span><span class="hljs-title function_ invoke__">imagecreatefromgif</span></span><span>(</span><span><span class="hljs-variable">$srcPath</span></span><span>);
</span><span><span class="hljs-variable">$filename</span></span><span> = </span><span><span class="hljs-title function_ invoke__">uniqid</span></span><span>(</span><span><span class="hljs-string">'img_'</span></span><span>, </span><span><span class="hljs-literal">true</span></span><span>) . </span><span><span class="hljs-string">'.gif'</span></span><span>;
</span><span><span class="hljs-title function_ invoke__">imagegif</span></span><span>(</span><span><span class="hljs-variable">$im</span></span><span>, </span><span><span class="hljs-variable">$destDir</span></span><span> . </span><span><span class="hljs-string">'/'</span></span><span> . </span><span><span class="hljs-variable">$filename</span></span><span>);
</span><span><span class="hljs-keyword">break</span></span><span>;
</span><span><span class="hljs-keyword">case</span></span><span> IMAGETYPE_WEBP:
</span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">function_exists</span></span><span>(</span><span><span class="hljs-string">'imagecreatefromwebp'</span></span><span>) || !</span><span><span class="hljs-title function_ invoke__">function_exists</span></span><span>(</span><span><span class="hljs-string">'imagewebp'</span></span><span>)) {
</span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">RuntimeException</span></span><span>(</span><span><span class="hljs-string">'當前 GD 不支持 WebP'</span></span><span>);
}
</span><span><span class="hljs-variable">$im</span></span><span> = </span><span><span class="hljs-title function_ invoke__">imagecreatefromwebp</span></span><span>(</span><span><span class="hljs-variable">$srcPath</span></span><span>);
</span><span><span class="hljs-variable">$filename</span></span><span> = </span><span><span class="hljs-title function_ invoke__">uniqid</span></span><span>(</span><span><span class="hljs-string">'img_'</span></span><span>, </span><span><span class="hljs-literal">true</span></span><span>) . </span><span><span class="hljs-string">'.webp'</span></span><span>;
</span><span><span class="hljs-title function_ invoke__">imagewebp</span></span><span>(</span><span><span class="hljs-variable">$im</span></span><span>, </span><span><span class="hljs-variable">$destDir</span></span><span> . </span><span><span class="hljs-string">'/'</span></span><span> . </span><span><span class="hljs-variable">$filename</span></span><span>, </span><span><span class="hljs-number">85</span></span><span>);
</span><span><span class="hljs-keyword">break</span></span><span>;
</span><span><span class="hljs-keyword">default</span></span><span>:
</span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">RuntimeException</span></span><span>(</span><span><span class="hljs-string">'暫不支持的圖片類型：'</span></span><span> . </span><span><span class="hljs-variable">$type</span></span><span>);
}
</span><span><span class="hljs-title function_ invoke__">imagedestroy</span></span><span>(</span><span><span class="hljs-variable">$im</span></span><span>);
</span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-variable">$filename</span></span><span>;
}
</span></span>要點：
檢測結果與保存函數匹配（PNG→ imagepng ，JPEG→ imagejpeg ……）。
團隊內若統一.jpg ，在生成文件名的時候做別名轉換即可，和image_type_to_extension()的返回值並不衝突。
如果你更習慣先拿MIME，再到擴展名，可維護一張自己的高質量映射表，而不是把MIME 直接丟給image_type_to_extension() ：
<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">ext_from_mime</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">string</span></span></span><span> </span><span><span class="hljs-variable">$mime</span></span><span>, </span><span><span class="hljs-keyword">bool</span></span><span> </span><span><span class="hljs-variable">$includeDot</span></span><span> = </span><span><span class="hljs-literal">true</span></span><span>): ?</span><span><span class="hljs-title">string</span></span><span> {
</span><span><span class="hljs-built_in">static</span></span><span> </span><span><span class="hljs-variable">$map</span></span><span> = [
</span><span><span class="hljs-string">'image/jpeg'</span></span><span> => </span><span><span class="hljs-string">'jpg'</span></span><span>, </span><span><span class="hljs-comment">// 業務偏好</span></span><span>
</span><span><span class="hljs-string">'image/png'</span></span><span> => </span><span><span class="hljs-string">'png'</span></span><span>,
</span><span><span class="hljs-string">'image/gif'</span></span><span> => </span><span><span class="hljs-string">'gif'</span></span><span>,
</span><span><span class="hljs-string">'image/webp'</span></span><span> => </span><span><span class="hljs-string">'webp'</span></span><span>,
</span><span><span class="hljs-string">'image/bmp'</span></span><span> => </span><span><span class="hljs-string">'bmp'</span></span><span>,
</span><span><span class="hljs-string">'image/x-ms-bmp'</span></span><span> => </span><span><span class="hljs-string">'bmp'</span></span><span>,
</span><span><span class="hljs-string">'image/tiff'</span></span><span> => </span><span><span class="hljs-string">'tif'</span></span><span>,
</span><span><span class="hljs-string">'image/svg+xml'</span></span><span> => </span><span><span class="hljs-string">'svg'</span></span><span>,
</span><span><span class="hljs-string">'image/vnd.microsoft.icon'</span></span><span> => </span><span><span class="hljs-string">'ico'</span></span><span>,
];
</span><span><span class="hljs-variable">$ext</span></span><span> = </span><span><span class="hljs-variable">$map</span></span><span>[</span><span><span class="hljs-title function_ invoke__">strtolower</span></span><span>(</span><span><span class="hljs-variable">$mime</span></span><span>)] ?? </span><span><span class="hljs-literal">null</span></span><span>;
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$ext</span></span><span> === </span><span><span class="hljs-literal">null</span></span><span>) </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">null</span></span><span>;
</span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-variable">$includeDot</span></span><span> ? (</span><span><span class="hljs-string">'.'</span></span><span> . </span><span><span class="hljs-variable">$ext</span></span><span>) : </span><span><span class="hljs-variable">$ext</span></span><span>;
}
</span></span>推薦策略：
用exif_imagetype()或getimagesize() → 獲得IMAGETYPE_* → image_type_to_extension() 。
如需統一風格（ .jpg等），做一層別名映射。
僅在必要時用finfo ，並用自維護表落地擴展名。
$image_type是否來自exif_imagetype() / getimagesize()[2] ？
是否把MIME/文件路徑誤傳進image_type_to_extension() ？
是否理解$include_dot的含義（是否需要帶點）？
團隊是否統一了.jpg / .jpeg的風格？映射是否生效？
寫入函數與檢測類型是否匹配（ imagejpeg vs imagepng等）？
環境是否支持目標格式（WebP/AVIF 等GD 能力）？
是否誤把.wbmp當成.bmp ？
是否避免信任$_FILES['type'] （客戶端可偽造）？
image_type_to_extension()本身很“老實”，所謂“返回錯誤擴展名”，多半是輸入不是IMAGETYPE_* 、團隊期望與規範不一致（ .jpg vs .jpeg ） ，或寫入環節與檢測結果不匹配。
沿著“正確獲取類型→ 合理做別名→ 匹配保存函數”這條路徑梳理，你就能把擴展名問題徹底拿下。
