編集2： 成功！mocakesさん、ありがとうございました！
透過性を維持しながら PNG を GIF に変換する正しい方法は次のとおりです。
$input = "data:image/png;base64,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";
$image = imagecreatefrompng($input);
imagesavealpha($image, true);
imagecolortransparent($image, 127<<24);
imagegif($image, 'img/test.gif');
GOSH！このような単純な数行のコードに 2 日 >__<
提案を投稿してくれたすべての人に感謝します。
古い投稿:
わかりました、私は今頭がいっぱいです。(なぜ PHP の GD ライブラリーはそれほど混乱しているのですか??) 私はこれに数時間2 日間取り組んできました..そして、PHP で透明な背景を持つ PNG から GIF を作成することができません。
これに関する StackOverflow に関する投稿がいくつかありますが、提供されたソリューションはどれも実際にはまったく役に立ちませんでした。私は常に黒の背景画像になるか、背景を除いて画像内のすべての黒が透明になります（またはすべてが黒のままです）。
と何度も入力imagecolorallocateしimagecolortransparentたため、これらのコマンドの意味が失われてしまいました.. >___<
私のコードは次のようになります。
$input = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAXwAAAEYCAYAAABfgk2GAAAemklEQVR4Xu2dzYsm13WHe7rHxGATtw1Zu8UMY0wIkv6AoF44ZOEspFWyUytkkRASJG0sgS2NPkCKF5qxMSSboNbOu4xJcAxZaJRNlhqRVYaZpPUPSC2wiYmm38k5rS75delW1b1V9+Pcuk9BMR/vrXvPfc6p33veU7eqLu2wQQACEIBAEwQuNTFLJgkBCEAAAjsIPkEAAQhAoBECCH4jjmaaEIAABBB8YgACEIBAIwQQ/EYczTQhAAEIIPjEAAQgAIFGCCD4jTiaaUIAAhBA8IkBCEAAAo0QQPAbcTTThAAEIIDgEwMQgAAEGiGA4DfiaKYJAQhAAMGvJwYeE1OfkP3JC5P3L/48vfjzlvz5nux36pkSlkIAAjkJIPg5ac8b60gOe1n2A8/DT6Tdddnf8WxPMwhAoBECCL5dRx+KaW8HCH1/Jir8T5Hx23UwlkEgNwEEPzdxv/E0q1exj7E9I50cx+iIPiAAgboJIPj2/Kfi/HRks7RPFX62dRLg+s46/Rp9Vgh+dKSLOoyZ2fcNIdNf5BqTB2u8cH3HpGtsGoXg2/HLoZjybmJzHpf+WcWTGHKG7jVWuL6TAfTahkDw7Xj0REz5ZmJzdIxHEo9B92kJxPwVyK++tL4y1zuCb8MlMU/iqRn9nTR4YaoRn5skcCxWcX3HpGvqMArBt+GnHNl9N9ON/GXPxrSxIoBAyqSATD/AETU3RfDLe09XWLyf2Qxq+ZmBLxzuUI7n+s5CiBy+w0vMDQTBs2LDjcx2PCfj3cw8JsPNJ5DjF6COwfWd+T6q4kgy/PJuui0m6DNycm76zB3NGtnsEzgSE2PdhDc1W0o7U4Qq/xzBL+9ABL+8DyxbkCO77+ZPlm85EiLYhuBHgLiwC10X/+jCPkIP1zG1js9mmwDXd2z7pzrrEPzyLish+B/ItFVM2GwT4PqObf9UZx2CX95llHTK+8CqBcSGVc9UaheCX95xnNTlfWDVAmLDqmcqtQvBL+84fraX94FVC0qU+7i+YzUaItiF4EeAuLALLswtBLjiw0sIPtd3VhxQCL4N556IGakfnNbN9EP5y4GNaWPFBAFKOoRIVAIIflScszs7kiO5uWY2vtUeiOCv1rVlJobgl+HuGjVHlk92b8ffPpZwfceHEm28CSD43qiSNzyUEXhAVnLMVQ3A9Z2q3GXfWATflo9SlnZ4TootX/tak+OXX2cLvwB9vVJpOwTfnuOOxaTYL7l4Rfq8bm+qWORBIGUS0B+epMDDITU3QfBtei/mSc5JbNPHIVblyPLJ7kM8UmlbBN+u4w7FNM325y7X1BP4Sdl5abldH/taprHA9R1fWrQbJIDg2w8Ozfa1HOMr/Cr02l6/LNjWQ0DjINXSXX4FridORmeC4NfjaF2xoZmeZu267V/8eXrx5y3587bsZPT1+DTUUv0S5/pOKDXaf04AwScYIFAXgZiZPpl9Xb5fbC2CvxghHUAgOwH9pafZvm+Zr28g13eyu8zGgAi+DT9gBQTmENBs/3qA8HN9Zw7lFR3TkuBv36b+UHz4vOw3V+RLptIuAa7vtOv7oJm3JPgq8tub/ns3iBaNIQABCFRMoBXBf0N89ILDT63Mv+IQxXQIQCAWgTUL3tSTBp+jpBMrjOgHAhCogcCaBb9fwtn2xw/kH6/X4CBshAAEIBCLQIuC/6bAezEWQPqBAAQgUAuB1gSfzL6WyMROCEAgOoG1Cf5Y3X5tc40eDHQIAQism8DaRHCsbr+2ua47MpkdBCAQncCaRHBqVc6a5ho9EOgQAhBYP4E1iOCU0KsXWYK5/lhmhhCAwASBNQj+WBmnm/4a5kkwQwACEFhEoHYh/L7M/rUJAmT3i0KEgyFgigDPxFrgjtoFfyi7R+QXBAWHQsAwAdc5X7uOZcNdO6i+838u5L6bjR4DQQACuQm4BJ8Ez9MLNQu+q5zDEzA9HU8zCFRKYOhXfc1als0VNULSd7nekP1ogFKNc8rmcAaCQOUEfin2f8UxB857D8fWBkmz+ldlH7Kbn3YeTqcJBComcCi2/6vsX+7NoTYtK+KC2iBxJ22RMGFQCJgj0NeC2rSsCNDaIG0Gsnsy+yLhw6AQKEbA9QY7Xls64Y7aBP/fZD7f4adcsZOMgSFghQAXb2d4oibBH7rJqqY5zHARh0AAAg4CQ3rAI9BHwqUGsdQ7694aKOXo1GqYA2csBCAQnwBJYCDTGsRy7EIttftAh9McAisj4BJ9svwBJ9cs+DXYvrJzi+lAwCQBHrfg6Rbrojn0k43M3tPBNINAAwTI8j2dbF3w+eb2dCTNINA4AbTCIwAsC77rW5uHo3k4lSYQaJAAWb6H0y0Lvusbm4ejeTiVJhBolABZ/oTjaxN8nY5lmxs9z5g2BEwQIMuvWPCH3lWL4Js4tzACAiYJkOWPuMW6eOI8k+cURkHALAGy/BUJPjdUmD3PMAwCZgiQKA64wnKG7/qmZv29mXMKQyBgloBLOyxrXTaQliGwSidbGDAQBFZHgOflO1xam+DrFPRi7nuy31ldiDIhCEAgFgEEvzLBH1ql001DHfpD2V+IFSH0AwEIrIYAgl+Z4HfmDr3lSj/Xz/ZWE6JMZC6B7hHaevxLsr8+tyOOWw0BBL9SwX9T7P7eSBhaLkut5uwxPpH+yc1qLuMOy2AeMVGp4HdmPyZ/eb/yOWSI8yaHcL3f9BtC4rRJGkxaCbA0cwViiRM5mV0EhlZ0Ud5pN15cSzO/3noSUFs5pH9i3xMH/pHsJ+3GdfMzH3pnQgdGS4IvNk+pTQCuX37PC4qbbeKo70Fkrgu4rNZpNXo/m/fYKzA7MtT024yRodioLdGN5r3aJj50AZfVOtFCoqqOXEt3/1Nm8Ae9WfBY7arcGs1YXnLeQ1mb4Kv5B7Ify/7ECuYSLbIb7Wjoms4bwqN/fwaP5WgzSPZl2h+jFZ8RqFHwO9/1T/bb8sEzsp+0GdfNzXoqe3PVb3ebo8SElQBr8i/ioGbBp57f7sns83J7V/bPBdw2Y4Y1+SsQ/KF6vjqXNdjrPbHHHrmxncAMteMC7npjY2hmLOdegeDrFA5kP5a9X89XBze9/Gql5/SY2Ltq9K5fAlzAXWlwjEyLxyWvRPCH6vld3Y5Mf10n95xldq4LuJR21hUXPrOhji+Uaq7hbzt5qKb7jjQ68okG2pgn4FO3D/lJr20p75h3ezQDEfwVCb5GhS6/utUr77A+P9r5Uqyj7kmYruTEd6nl2N24ZPvFXJt14L7g+8ZOViNTD7aWDL/j5FpzSxaXOorS9T/1ToSQ+HWVdjrLEf10PrTSM8t0V5bhd4HlqvM+Ih+eWIk87PAmMPbYhDkZ2limT2Lg7ZYqG7JSZ6WCP3RS35b5HsuudX022wTUh68OxGcMYXZl+6zesR0TS61z/VoM+YW4dHwTx691wmOZIUs2TYTeoBFalvtoQOznZPVDA7lEP8aXiW26bVvX/IXbtQr+VO1Xw56T2+bJ/1Mx608HTIsdr9R1bcZACqtYi7/Sks52sBzJP3Tv35jVtdFn7xyniC76DCYwthpHO4uZ3XfGuUSARCDYdVUcQA2/AcHvIvFA/vI/A2GJ6Ns4X4fKcKnfUsQzd2z4P7UVPE+nIcHXYJoq85DZpT7l3P2nvkA7NauhLxqWak6Rq+dzyjkXvopdE60hBLTE8/aAoZzk+Tw4VcLJ9QU8lggQD/niIeVIlHMaFnyd+pjo/6N8/hcpo6/xvnUVzo0LHwyhyCX22+MP3ZiF6NcfsJRzGhd8nf7YTTi35XNephL3RB8r3WyPVELsu/ER/bg+t9Jb88sxO0e0WNLpB+HQSa5B8hPZ/9ZK1FZoh6/I69RKCr1Ppq9tUqwUqtCt1ZmM4JPh/1bQ/lj+9TcDYazrwl+U/aS6MC9r8Niza/qWWRPSsSSA1ySWjas5oyP4CP4X4uZA/udY9qE1+/qZPpbh9pyIa+yYsXJZh0JZ6gXTU6NshkSfX8VGHeYwa2hhQLM+bHbiIzGrF23/fOTzO/LZzQvxryf001vqW76xUrrxIcJyPh9KdtvMeWGO3dlEsAzBd0P0yVA1mF6S/fUIfqi9i6nyTc0rXfqiUfNcao+zUPtdgl9TwhE638n2CP44oqOLssOjEyRbDKKpdfTbyGqOs6Es0dp1h8mTvcEGLMfsOb3mEzFn/B7KYCr+TwcOeiztVRis1ql9puNbqhnqq3ZhHPq1x+OUfaKnXBvXr87m9a55AIHxeCDt9Sf90NMcx7qrRfyXCvwaSx5DJasWf9kFnjJFmg99STevd80DmBmOPjX+GsR/qbj357hmAXT5nCx/5gmU+DBq9wOAEfxlkbdU+ENH/4Uc8A+y/8zjwNhiPjZk7WUbD5znTcbKO8/L57p6i608AS60I/hZo1CfF6Mnf2jNP6uRgYOtOXsPQTF0EZdsP4RiurYspR1hS4afLvC6nmsVfwTeHRu8CD39OTN3BG6WmyCH4M8NrXnHWRV/xD3Mn4h+GK/UrfW8+nvZ/4xKxjhqBD91KMbr/0np6i9l/+PALhHzQGABzV3lHUo7AQAXNvW5TtXK9SUvlAi+FyYaQcBJYOzlKQhNuqDxEfo1Lg9eTBTBX4yQDiCwQ6afJwh87+7mVy21rTwRyShNEhiq6SM8ccNhaIVUN4r1J7DGpTGjNzL8GdA4BAIOAtyYlTYsxspnfLF6skfwPUHRDAIeBMj0PSDNaDIk9gh9IEwEPxAYzSEwQWCo7MBFxLDQ8bkwi36FMd0BWCAwmkNggsDU4zbISscB+l6YZRXUjFMRwZ8BjUMgsFD0yfZ/G6CvyHdHIfYzT0EEfyY4DoOAB4GpN4FpF62L19jFWBfi1nl5hN1wEwR/ET4OhsAkgakSj3bQWpnHpz7fgW2NzWRALWmA4C+hx7EQ8Cfgk+2vOeMPEXlKN/5xFdQSwQ/CRWMILCLgk+2vMeP3/bJb8xfeosCJdTCCH4sk/UDAn4Bv3brGevWcTJ6M3j92FrVE8Bfh42AILCKwloxfH098Q3Z94U+IplCfXxQ+4QeHOCe8d46AAAR8CPhm/KUFckn23nFgSapPRCRqg+AnAku3EJhBwDfj73e99IsghpD7THepnT5j0GaEAIJPeEDAFgHfbN+W1V+0BnE36CEE36BTMAkCFwTmZvylAPJ44lLkPcdF8D1B0QwCBQlYE36y94LBsGRoBH8JPY6FQFkCsb8IEPKy/kw+OoKfHDEDQAACELBBAMG34QesgAAEIJCcAIKfHDEDQAACELBBAMG34QesgAAEIJCcAIKfHDEDQAACELBBAMG34QesgAAEIJCcAIKfHDEDQAACELBBAMG34QesgAAEIJCcAIKfHDEDQAACELBBAMG34QesgAAEIJCcAIKfHDEDQAACELBBAMG34QesgAAEIJCcAIKfHDEDQAACELBBAMG34QesgAAEIJCcAIKfHDEDQAACELBBAMG34QesgAAEIJCcAIKfHDEDQAACELBBAMG34QesgMBaCRzKxP5Z9q/K/lD252W/udbJWp8Xgm/dQ9gHgboJnIr5X+tNAd0p5FPAFwLPsBBohACCb8jRCL4hZ2AKBFZIQEs675Lh2/Asgm/DD1gBgbUS+L5M7DUE34Z7EXwbfsAKCKyVwEYm1teZ5+T/uHBbwOMIfgHoDAmBhgjoyhzXhvYUCAKgF4DOkBBoiICrpKPT/4HsrzfEwcRUEXwTbsAICKyawL7M7mPHDNGfzG4HeGbgDAeBRglw8daA4xF8A07ABAisnMCzMr+3ZO/rDfqT2fEAzwyc4SDQIAEu3BpxOoJvxBGYAYEVE0DwjTgXwTfiCMyAwIoJaEnnBhdty3sYwS/vAyyAQAsEXFk+SzMzex7Bzwyc4SDQKAHXKh39EthtlEeRaSP4RbAzKASaJECWX9jtCH5hBzA8BBoi4BJ8svyMAYDgZ4TNUBBonACrdQoHAIJf2AEMD4GGCLBap7CzEfzCDmB4CDRGwJXlo0OZggDQmUAzDAQgcE4AwS8YCAh+QfgMDYEGCbiWZ7IeP1MgIPiZQDMMBCDwOYF+ls9KnUzBgeBnAs0wEFhA4Cdy7F/3jleRfF72Gl8VSFlnQTAsORTBX0KPYyGQh8DQckYdvcZz2DUf3nObIZZqDJYMWBgCAqYItCD4tX55mQqUKWMQ/ClCfA6B8gRcJZ3OqhrPYW7AKhRTNQZLIVQMC4HiBPorXGotg3ADVqFQQvALgWdYCDROgAepFQgABL8AdIaEAAScN2BRx08cGAh+YsB0DwEIOAkM1fFrLVNV4WYEvwo3YSQEVkdgbSuPqnAQgl+FmzASAqsjgOAXcCmCXwA6QxYnoKtE3rqwIuXdqrnGKQ50hgFjgk9ZZwZQn0MQfB9KtFkbgW2xSfkcl76oIWS/iaQxwefibaIzDsFPBJZuTRPoi83XxdrTBBbzkLBhqAh+goCb6hLBnyLE52sksJFJbcf+O/LvowQT5SFhCH6CsJrfJYI/nx1H1kvgWEx/umd+inILgo/gmzpLEHxT7sCYTAT2ZZyPe2OlqOW7HiEQ+2UftV4YpqSTKdi3h0HwC0BnSBMEXILzjFim2X/MLXUdP9cF6JhMtK+h5+l046BNsYlLf0BNAJUuqyAwJDg/F+u/G3EGrlf6xTzv+l8oMfuOiMHZFWvxUxPu9V9TcGRGw3ANEHCJsU479nmRUpRT9p06BBD81IQR/MyEGc46gRwXVvtjxKrjvylwv1fxOT0m+LEYWY+/rPbFzmSyGs9gEIhAwCU6j0i/JxH67rpIVcfPYXtEDF/oigu3Kek6+kbwMwNnOHME+mvy1UAVoh/K/kIka1PV8XPYHgnBF7qZumirB6BPkekDNDJQo909JnY9IfuTF/bpskTdurtLb8nf35P9jlH7U5rlKovoeCqmexEH7mez6oufLew/l+0LzZwl9npQqjugY8+nmv4Q/CiuuiuCuieCurkQ1N0LQd1cCOquCOqZCOq13IJ6JNN7WfYDz2meSLvrsuudpy1tyudYdv1S3N5iCc5YNrv0hq/UtqeIg6lSzvaYS/mksL/aPqsQ/Lv7B4/tbTZPbC596VxQNzuXzgV1d+fhuaDuPvz01tnu7nvXTk8yC+pdEdS9QEH9PxHUb6cW1EPB8rbsKgZzthM56CnZM/OcY2rUY/pCpPF1U/YfyR76rB0t47wq+9Q5FuuXhOs6QcongS4B7xJ8FfYbjk5T3BC3xPaqj50KxqKTu7t/5Wj34YOXd/a+5CdcZ5+efPrg8vVv/+p+YkF9XwT1dxcK6pkIapKMX76EzsU+xpbiRqQYdqXqYyjz1P/3FU9fod+eQ4wVKS7brYrl0Moo17UOq3NIFYNJ+zUp+P+xf/Xw9x5++ra30PcRifBvLl16Kk3Gf57VRxLUMxHUa8cRPax9PR2xP+1K+1Thb2EbWpffzX2svNA94mDOORVD1HLdUxAjDijpxKA4o485wTljGP9DzrP63UtRBHWzefjMtdP7EQX1nvR1KbKgPpQ+r8YQVPkiipbZ9x3WUqav5UIVb92/1gMxJMw+K062vzS+Kv94rdd3jHNRbe8/I+in8n9/JXtoScr/pA1vGcIrBpdwC1d6hCmY975xIOJ3ObKgbo6vfvTfEQQ1Zmbfj6bFmf6h9Phu4hh9XPpvqabvEk9F3D9npsRrqFzTz3JjnYtDpR3fklTiMPq8e98sPxaXXPMyPY4ZmDEz+z7x5Zn+ec0+saCeiaDOrumfyJy/mTjSdAy9IamlzSXm/XNmSLim6vKpBH+sLGVpxcvUF6XGmSV7VxH3JgT/vGa/mzZD3WwePD6/pn8/k6BemSOoRxKJUUpgHhHdUmmnwzEmzGOiNXVupRJ8tfsN2YduGoux/t8jVGhikcBUUGax+d7+wcnO7uW0GapcyL36yYczBDVlKaePd1ZpJ8eXUWdoi1l+X5g169QXoI+dOz6ZqatfXQIaaxsqSWn/IauOYtlDPwYIFBf8lKWcPt95pZ0s2f2WoAZl+XLD1877meOotVq+b625c4PvOdXvN8ZKnX4ojP0CibX+P3P4MdwSAr7BuWSM0WOzZPedBcFZ/vkdtJkFNaiW71MHje07n+w19pgl+wsR/BA2Q2vRY891Sdkpti30V5hAUcHXO2h3dy9nFdSwWv79QoJ6xfen/W2Jnycyx9B7Mt5h5jFLDRfi/xCx1/m4+p660LuEg9bu/6nXQdHzf8lkOHYegaIOv79/8OzD3cuu26nnzcbjqEubB89dOT3xFNS7Iqj6jJyc2/kzd3wFFcFP65qp7D5U5PvW5ijrbI/ZH48LuGnjx1zvRQX/7v7V27u7eTPUzWZHnrlzz1NQzQu+rot/NHNU6Zhax29hGxP8pWKv/P5d9j/sgUx5jaSWNfotxFaROSL4o9jvFxLUK76CWsK+DwSZXixuYUtdZx/6QtH/j/k8/s5Xrufn62dcwG0hmmWORQX/v/av3tnbzZuhnp3t3PnWJ/c8BbWI4IugXvEVVEo6aU9UnxuvllgwJMCpRJgLuEu8tYJj2xP8zc4H3zq95ymo5ks6CH76kzDlDVJDLzDpZrXkefyH0sm/yP4V2bfX3Q+JflEtSO9GRlACRZ1MDd8VhEEXbUNWkcSK+Bi161i25OgnpeCr/WPXCX4tnx/L/qLsp4GT1fb9h78NdZFydVCg2TRPSQDBH6VrflkmN16lPDs+67uk4HezUxtekv31gOmGCH5RHQiYE00XEijq6AqWZVq/8UrdfyJ72sdS/CbIPpS/HiyMudoOtyD4yiz0wuqhHPML2X9nAnjJX2xTv1B5BETks6Wo4Nu/8UppZ320ggjqlVBBPRIjeXha5BNjqzsrgj/n0Qtjz9PRKZYUex1/6j6Hzg1zfuGki4iKey4q+Mot66MVNg8+vHp6Eiio5h+ephhPZE+d5beY3btEKfY5M5Tl/q8Mflf27j6LuXX27f7n9pFK4nwFvxvf4stcUrFJ0m/s4A020v7D07Jl+XOy+473ofzl3WD4YQekvCEozJK8rfuilEI0Xc+w/0SmqRn6mrdQwe++gK29zKUaHxUX/GxZ/qzsvvOj+RegqKFHsqcq7TwjfR9XE9VxDc31+INt0f+VTOFPZL8ddyrmevulWKTLRnXTOeurH6fq+t0kqO/PcKcJwbf/AhQlm7K0M+s5+C53qyg/PSMOxg55RT68HrnPmrpzZd8mzpuaIA7Yeij/f+viM32uT/cF55v5z7musQJs86dgJnBTlnbmPQffBTXFS8x/LYL6+zEF9Ugsj5Xpt5zZdwGA4M/Xl7lH+gq+9m9Gw+ZONudxpmCleIm5/E585dGP7kUU1JiZfrTMvh8zmjlptj/3Qq5eoNWMS5/V0/rmevyBxtOPZA+9Gap1lr7zDxH80iuNfOdkop0pwVciMTP9eJl931fnNf2Fgnomgjr7peW+wXMkDVWcfIVfhV7b69zYPiMwJD4q9k/JfhtQ0Qn41vG7gc3pWHQikTo0Ceq8pr/z4Hj2e27lAq2kZU/Of2m5L93zbD9QUM+k/bXcgqp35B7Krlm7bt3qjy5D1TqqChcZ/Rdd7yrpdK2Unz7vhi0+gZAs36SOxUeyvEfToM6z/R0RSN8XnJ8L/d71a6f3Mwvq+asQRVA1a9dt70JQzy4EdU8E9UwENXlGvzwi6MFFQP2pWafu28+nafXehBxRguAnoGxa8Lv56h25e5Khnu1cPhdUiYRzQRXjzwV1b+fBrTPJUNNn9Ak8QJc1EdgWfrV7e2VJTfOowdaQsk4VOmYBOqAseAEbIACBIQI+mT465hk/gPIERTMIQKAIgalMn1U6AW5B8ANg0RQCEIBAzQQQ/Jq9h+0QgAAEAggg+AGwaAoBCECgZgIIfs3ew3YIQAACAQQQ/ABYNIUABCBQMwEEv2bvYTsEIACBAAIIfgAsmkIAAhComQCCX7P3sB0CEIBAAAEEPwAWTSEAAQjUTADBr9l72A4BCEAggACCHwCLphCAAARqJoDg1+w9bIcABCAQQADBD4BFUwhAAAI1E0Dwa/YetkMAAhAIIIDgB8CiKQQgAIGaCSD4NXsP2yEAAQgEEEDwA2DRFAIQgEDNBBD8mr2H7RCAAAQCCCD4AbBoCgEIQKBmAgh+zd7DdghAAAIBBBD8AFg0hQAEIFAzAQS/Zu9hOwQgAIEAAgh+ACyaQgACEKiZAIJfs/ewHQIQgEAAAQQ/ABZNIQABCNRMAMGv2XvYDgEIQCCAAIIfAIumEIAABGomgODX7D1shwAEIBBAAMEPgEVTCEAAAjUTQPBr9h62QwACEAgggOAHwKIpBCAAgZoJIPg1ew/bIQABCAQQQPADYNEUAhCAQM0EEPyavYftEIAABAIIIPgBsGgKAQhAoGYCCH7N3sN2CEAAAgEEEPwAWDSFAAQgUDMBBL9m72E7BCAAgQACCH4ALJpCAAIQqJkAgl+z97AdAhCAQAABBD8AFk0hAAEI1Ezg/wFm7lJkZahzkgAAAABJRU5ErkJggg==";
list($ignore, $imgData) = explode(',', $input);
$image = imagecreatefromstring(base64_decode($imgData));
imagealphablending($image, true); // setting alpha blending on
imagesavealpha($image, true); // save alphablending setting
//my code works up until this point (I can output a transparent PNG successfully)
//this is where I would make a new image with-
//the transparent background and put my transparent PNG on it-
//to prep it for imagegif();
//i kinda had some success with:
//$fill = imagecolorallocate($image, 255, 250, 214);
//imagefill($image, 0, 0, $fill);
//just to test if I could actually change the background..
//but anything like a circle with a transparent center would not--
//get filled with transparency and would remain black.
//so this obviously isn't the way to do it.
imagegif($img, 'test.gif');
最終結果は、PNG の透明な背景を保持する GIF でなければなりません。
私は本当に立ち往生しています ¬____¬ 助けてください。
あなたが提供できるアドバイスを事前に感謝します。
編集: chrislondon の 2 番目の例が機能しない理由の例を示すために、この画像に半円と完全な円を描画し、chrislondon のコードを使用して回転させました (結果として、.GIF 画像が必要になります):
(ゴツゴツした) 黒い円は私が塗りつぶしたものではありません。中央の透明度が透けて見えないだけです。右側の (ゴツゴツした) 円は、隙間を残して完全に完成していないため、透明部分が塗りつぶされています。
これにより、私が達成しようとしていることに対する残りの誤解が解消されることを願っています。