Bug: imagewebp(): Palette image not supported by webp

[stevy80]

PHP Version

8.2

CodeIgniter4 Version

4.4.2

CodeIgniter4 Installation Method

Composer (as dependency to an existing project)

Which operating systems have you tested for this bug?

Linux

Which server did you use?

apache

Database

MySQL 8

What happened?

When converting some .png images to .webp with the using of the image library (gd), the following error occurs: imagewebp(): Palette image not supported by webp

Steps to Reproduce

$image = \Config\Services::image(); 
$image->withfile($filePath); // $filePath to the png file
$image->convert(IMAGETYPE_WEBP);
$image->save();

Expected Output

valid webp file

Anything else?

currently the code in the GDHandler.php (save function):

// for png and webp we can actually preserve transparency
if (in_array($this->image()->imageType, $this->supportTransparency, true)) {
   imagealphablending($this->resource, false);
   imagesavealpha($this->resource, true);
}

if I use imagepalettetotruecolor there, the problem solved for me, like:

// for png and webp we can actually preserve transparency
if (in_array($this->image()->imageType, $this->supportTransparency, true)) {
   imagepalettetotruecolor($this->resource);
   imagealphablending($this->resource, false);
   imagesavealpha($this->resource, true);
}

[vini123]

虚幻之物对应着冥冥之路！：《羽》

[kenjis]

Cannot reproduce. The following test passes without errors. Does it depend on the source PNG file?

--- a/tests/system/Images/GDHandlerTest.php
+++ b/tests/system/Images/GDHandlerTest.php
@@ -412,6 +412,14 @@ final class GDHandlerTest extends CIUnitTestCase
         $this->assertSame(exif_imagetype($this->start . 'work/ci-logo.png'), IMAGETYPE_PNG);
     }

+    public function testImageConvertPngToWebp(): void
+    {
+        $this->handler->withFile($this->origin . 'ci-logo.png');
+        $this->handler->convert(IMAGETYPE_WEBP);
+        $this->handler->save($this->start . 'work/ci-logo.webp');
+        $this->assertSame(exif_imagetype($this->start . 'work/ci-logo.webp'), IMAGETYPE_WEBP);
+    }
+
     public function testImageReorientLandscape(): void
     {
         for ($i = 0; $i <= 8; $i++) {

[stevy80]

Yes, it depends from the png. Some works (like ci-good.png), some not (ci-bad.png).

[kenjis]

@stevy80 Thank you! I sent a PR #8210