PHP GD Resizing Causes Artifacts - php

Question

I have a function that I'm using to accept user-uploaded images, proportionally scale it to a have a maximum width/height of 4,000px, and also generate 400px and 800px thumbnails. It needs to be capable of handling transparent PNGs and applying a white background.
My current code does all of this, however, it adds undesirable artifacts not typical of JPEGs. They're vertical striations and look like a very washed out barcode when viewed close up (400% Zoomed Screenshot attached). This even occurs on the original image when uploaded at the size it's being scaled to. It seems to be even more prevalent with transparent PNGs, but happens in white regions of JPEGs as well. JPEGs are being saved with Quality 80.
function resize_image($file, $w, $h, $strict = false, $crop = false, $path = null, $thumbnail = false)
{
// Check for Valid Image + Calculate Ratio
list($width, $height) = getimagesize($file);
if (empty($width) || empty($height))
{
echo json_encode(['result' => 'error', 'error' => 'file_format_invalid']);
http_response_code(405);
exit;
}
$r = $width / $height;
if (!$strict)
{
$w = min($w, $width);
$h = min($h, $height);
}
$wTa = min($w, 400);
$hTa = min($h, 400);
$wTb = min($w, 800);
$hTb = min($h, 800);
// Apply Crop Constraint
if ($crop)
{
if ($width > $height)
{
$width = ceil($width - ($width * abs($r - $w / $h)));
$widthTa = ceil($width - ($width * abs($r - $wTa / $hTa)));
$widthTb = ceil($width - ($width * abs($r - $wTb / $hTb)));
}
else
{
$height = ceil($height - ($height * abs($r - $w / $h)));
$heightTa = ceil($height - ($height * abs($r - $wTa / $hTa)));
$heightTb = ceil($height - ($height * abs($r - $wTa / $hTb)));
}
$newWidth = $w;
$newHeight = $h;
}
else
{
if ($w / $h > $r || $r < 1)
{
$newWidth = $h * $r;
$newWidthTa = $hTa * $r;
$newWidthTb = $hTb * $r;
$newHeight = $h;
$newHeightTa = $hTa;
$newHeightTb = $hTb;
}
else
{
$newHeight = $w / $r;
$newHeightTa = $wTa / $r;
$newHeightTb = $wTb / $r;
$newWidth = $w;
$newWidthTa = $wTa;
$newWidthTb = $wTb;
}
}
// Create, Resample + Return Image
$src = imagecreatefromstring(file_get_contents($file));
$dst = imagecreatetruecolor($newWidth, $newHeight);
$fff = imagecolorallocate($dst, 255, 255, 255);
imagefill($dst, 0, 0, $fff);
imagecopyresampled($dst, $src, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);
if (!is_null($path))
{
imagejpeg($dst, $path, 80);
if ($thumbnail)
{
$dstThumbA = imagecreatetruecolor($newWidthTa, $newHeightTa);
$dstThumbB = imagecreatetruecolor($newWidthTb, $newHeightTb);
$fffThumbA = imagecolorallocate($dstThumbA, 255, 255, 255);
$fffThumbB = imagecolorallocate($dstThumbB, 255, 255, 255);
imagefill($dstThumbA, 0, 0, $fffThumbA);
imagefill($dstThumbB, 0, 0, $fffThumbB);
imagecopyresampled($dstThumbA, $src, 0, 0, 0, 0, $newWidthTa, $newHeightTa, $width, $height);
imagecopyresampled($dstThumbB, $src, 0, 0, 0, 0, $newWidthTb, $newHeightTb, $width, $height);
imagejpeg($dstThumbA, str_replace('.jpg', '-thumb.jpg', $path), 80);
imagejpeg($dstThumbB, str_replace('.jpg', '-thumb#2x.jpg', $path), 80);
}
}
return $dst;
}

Answer 1

I concluded that the issue is specific to the environment (occurs on PHP 7.1.3 under Ubuntu, but not under PHP 7.0.1 on Windows). Reinstalling php7.1 and php7.1-gd had no effect.
Ultimately I decided to bite the bullet and rewrite with ImageMagick, resulting in a much more concise block of code:
$magickSource = new Imagick();
$magickSource->readImageBlob(file_get_contents($file));
$magickSource = $magickSource->flattenImages();
$magickFull = clone $magickSource;
$magickFull->resizeImage(min($originalWidth, $newWidth), min($originalHeight, $newHeight), Imagick::FILTER_LANCZOS, 1, true);
$magickFull->setImageCompression(Imagick::COMPRESSION_JPEG);
$magickFull->setImageCompressionQuality(75);
$magickFull->stripImage();
$magickFull->writeImage($path);
$magickFull->destroy();
if ($thumbnail)
{
$magickThumb = clone $magickSource;
$magickThumb->resizeImage(min($originalWidth, 400), min($originalHeight, 400), Imagick::FILTER_LANCZOS, 1, true);
$magickThumb->setImageCompression(Imagick::COMPRESSION_JPEG);
$magickThumb->setImageCompressionQuality(75);
$magickThumb->stripImage();
$magickThumb->writeImage(str_replace('.jpg', '-thumb.jpg', $path));
$magickThumb->destroy();
}
The calls to setImageCompression(), setImageCompressionQuality, and stripImage() yielded a 53% reduction in combined filesizes. (Source)