Crop part of image in php and resize it

I have a source image (can be any image with and have different dimensions). I want to be able to tell php an area from the image to crop out and resize. For example:

• The source image is 800x800 pixels.
• PHP selects a 50x50 pixel region of the image with the selection area starting 80 pixels from the top edge of the source image, and 100 pixels from the left edge of the source image
• The selected region is then resized to 37x37 pixels.

I tried using the functions imagecopyresampled() and imagecopyresized() but they both gave me a weird problem: imagecop开发者_StackOverflow中文版yresampled() outputs the selection image but is surrounded by a black area equivalent to the dimensions of the source image. imagecopyresized() also selects the selected region, but it is just overlayed on the source image. The end goal here is to make thumbnails from the source image.

An example of the code I am already using is:

list($width_orig, $height_orig) = getimagesize($filename);
imagecopyresized($image_final, $image, 0, 0, 0, 0, 37, 37, $width_orig, $height_orig);

The above does not do exactly as the task describes, but it demonstrates the problem that I am running into.

Note:

I understand that doing a search on this topic leads to a lot of results but they mostly reference libraries and classes that do a lot more than I actually need. I'd rather have an understanding of the solution and implement something more efficient. Hence, I am not looking to be pointed to an exhaustive script that accomplishes the above task and 50 other tasks. I'd rather understand the above so I can create an optimal, custom solution.

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Your question is in fact a logic question. Can you check that snipped? Scales if it does not fit crops out longer part.

    $w  = imagesx($img);
    $h  = imagesy($img);
    $newImage = imagecreatetruecolor($wNewOrj, $hNewOrj);
    if(($w/$h)<($wNewOrj/$hNewOrj)){
      $hNew = $h * $wNewOrj/$w;
      $wNew = $wNewOrj;
    }else{
      $hNew = $hNewOrj;
      $wNew = $w * $hNewOrj/$h;
    }
    $wDiff  = round(abs($wNewOrj-$wNew)/2);
    $hDiff  = round(abs($hNewOrj-$hNew)/2);
    imagecopyresampled($newImage, $img,
                       0,     0,     $wDiff,    $hDiff,
                       $wNew, $hNew, $w-$wDiff, $h-$hDiff);

    imagejpeg($newImage, $path, 85);