关于php切图问题引发的疑惑

有时候写代码挺好奇的，触及到了我的知识盲区。
我有一张jpg的图片，切图生成新的图片，新的图片和原图颜色并不是完全一致，我问过chatGPT也并没有很好的解决。但是我换成nodejs重写切图逻辑，新图和原图颜色就是完全一致的。
如果我要搞清楚这是怎么回事，我应该怎么去做呢？

这里提供代码，请大家指点一下。

<?php

$split = function ($sourceImage, $outputPath, $splitType, $overlapRatio = 0.2) {
  list($width, $height, $type, $attr) = getimagesize($sourceImage);
  $symbol = "w";
  if ($splitType == 1) {
          $sliceWidth = ceil($width / 4);
          $overlapWidth = (int)($sliceWidth * $overlapRatio);
          $sliceWidthWithOverlap = $sliceWidth + $overlapWidth;

          for ($i = 0; $i < 4; $i++) {
              if ($type == IMAGETYPE_JPEG) {
              $image = imagecreatefromjpeg($sourceImage);
              $ext = ".jpg";
              $create = "imagejpeg";
          } else {
              $image = imagecreatefrompng($sourceImage);
              $ext = ".png";
              $create = "imagepng";
          }
          if (!$image) {
            throw new Exception("Failed to load the image.");
          }
          $slice = imagecreatetruecolor($sliceWidthWithOverlap, $height);
          $srcX = $i == 0 ? $i * $sliceWidth : $i * $sliceWidth - $overlapWidth;
          imagecopyresampled(
              $slice,
              $image,
              0, 0, // 目标 x, y  $srcX, 0, // 源 x, y  $sliceWidthWithOverlap, $height, // 目标宽度, 目标高度
              $sliceWidthWithOverlap, $height // 源宽度, 源高度
          );
          $create($slice, "{$outputPath}{$symbol}_{$overlapWidth}_{$i}{$ext}");
          imagedestroy($slice);
          imagedestroy($image);
          }
     } else {
      $symbol = "h";
      $sliceHeight = ceil($height / 4);
      $overlapHeight = (int)($sliceHeight * $overlapRatio);
      $sliceHeightWithOverlap = $sliceHeight + $overlapHeight;

      for ($i = 0; $i < 4; $i++) {
          if ($type == IMAGETYPE_JPEG) {
              $image = imagecreatefromjpeg($sourceImage);
              $ext = ".jpg";
              $create = "imagejpeg";
          } else {
              $image = imagecreatefrompng($sourceImage);
              $ext = ".png";
              $create = "imagepng";
          }
          if (!$image) {
              throw new Exception("Failed to load the image.");
          }
          $slice = imagecreatetruecolor($width, $sliceHeightWithOverlap);
          $srcY = $i == 0 ? $i * $sliceHeight : $i * $sliceHeight - $overlapHeight;
          imagecopyresampled(
              $slice,
              $image,
              0, 0, // 目标 x, y  0, $srcY, // 源 x, y  $width, $sliceHeightWithOverlap, // 目标宽度, 目标高度
              $width, $sliceHeightWithOverlap // 源宽度, 源高度
          );
          $create($slice, "{$outputPath}{$symbol}_{$overlapHeight}_{$i}{$ext}");
          imagedestroy($slice);
          imagedestroy($image);
      }
 }};

这是nodejs代码

 //npm install sharp
const  fs  =  require('fs').promises;
const  path  =  require('path');
const  sharp  =  require('sharp');

async function split(sourceImage, outputPath, splitType, overlapRatio  =  0.2) {

     try {
         const  imageBuffer  =  await  fs.readFile(sourceImage);
         const  metadata  =  await  sharp(imageBuffer).metadata();
         let  extension  =  path.extname(sourceImage);
         let  createSharpFunction;

         if (extension  ===  '.jpg'  ||  extension  ===  '.jpeg') {
             extension  =  '.jpg';
             createSharpFunction  =  sharp().toFile;
        } else  if (extension  ===  '.png') {
             extension  =  '.png';
             createSharpFunction  =  sharp().toFile;
        } else {
             throw  new  Error('Unsupported file format.');
        }

         const { width, height } =  metadata;
         let  sliceWidth, sliceHeight, overlapWidth, overlapHeight, sliceWidthWithOverlap, sliceHeightWithOverlap;
         let  symbol  =  'w';
         let  slices  =  4;

         if (splitType  ===  1) {

             sliceWidth  =  Math.ceil(width  /  slices);

             overlapWidth  =  Math.floor(sliceWidth  *  overlapRatio);

             sliceWidthWithOverlap  =  sliceWidth  +  overlapWidth;

        } else {

             symbol  =  'h';

             sliceHeight  =  Math.ceil(height  /  slices);

             overlapHeight  =  Math.floor(sliceHeight  *  overlapRatio);

             sliceHeightWithOverlap  =  sliceHeight  +  overlapHeight;

        }

     for (let  i  =  0; i  <  slices; i++) {

             let  croppedImage  =  sharp(imageBuffer);

             if (splitType  ===  1) {

             let  srcX  =  i  *  sliceWidth  - (i  >  0  ?  overlapWidth  * (i  -  1) :  0);

             let  endX  =  srcX  +  sliceWidthWithOverlap;

             if (endX  >  width) {
                 srcX  -=  endX  -  width;
                 sliceWidthWithOverlap  =  width  -  srcX;
            }

             await  croppedImage.extract({
                     left:  srcX,
                     top:  0,
                     width:  sliceWidthWithOverlap,
                     height:  height
            }).toFile(`${outputPath}${symbol}_${overlapWidth}_${i}${extension}`);

        } else {

             let  srcY  =  i  *  sliceHeight  - (i  >  0  ?  overlapHeight  * (i  -  1) :  0);

             let  endY  =  srcY  +  sliceHeightWithOverlap;

             if (endY  >  height) {

                 srcY  -=  endY  -  height;

                 sliceHeightWithOverlap  =  height  -  srcY;

            }

         await  croppedImage.extract({
                 left:  0,
                 top:  srcY,
                 width:  width,
                 height:  sliceHeightWithOverlap

            }).toFile(`${outputPath}${symbol}_${overlapHeight}_${i}${extension}`);
        }

    }
} catch (error) {

     console.error(`Error processing the image: ${error.message}`);

  }

}

split('img/height.jpg','img/',2).then(log=>{
     console.log(log);
})

这里提供一张图片，大家可以复制代码下载图片在直接本地测试使用。

最后，非常感谢你花时间阅读，如果你有什么想法，欢迎讨论交流。