Image quality issue if converted Png to Jpg

[ray-kudos]

Magick.NET version

Q8-AnyAPU 13.5.0

Environment (Operating system, version and so on)

Windows 10 Pro 20H2

Description

Hi,

I am trying to convert a png format image(11554_original.png) to jpg format(11554.jpg) and found out the jpg image is broken.
11554.png was OK, but 11554.jpg wasn't properly converted. I was wondering what I missed here.

Steps to Reproduce

1. Save as png
   string fullFileName = "c:\temp\11554.png";
   using (var image = new MagickImage(bits))
   {
   image.Format = MagickFormat.Png;
   File.WriteAllBytes(fullFileName, image.ToByteArray());
   }

2. Save as jpg
   string fullFileName = "c:\temp\11554.jpg";
   using (var image = new MagickImage(bits))
   {
   image.Format = MagickFormat.Jpg;
   File.WriteAllBytes(fullFileName, image.ToByteArray());
   }

[dlemstra]

A jpeg image has no transparency and when your png file is written the alpha channel is disabled and the pixels behind it are shown. I would advise you to specify the background color with the following method:

using var image = new MagickImage(@"c:\temp\11554.png");
image.ColorAlpha(MagickColors.White);
image.Write(@"c:\temp\11554.jpg");