Artifacts on the image extracted from gif

[KubaZ2]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am using the latest version of Magick.NET
• I have searched open and closed issues to ensure it has not already been reported

Description

I have the gif:

I use MagickImageCollection to storage it.
I want to get the 5th frame of it, I make it using imageCollection[5], expected result:

but the Magick.net gives me this:

(it has transparent holes)

That is strange, because if I make a gif from the imageCollection, it looks good (to be honest, the original gif is a gif processed by Magick.net and there was the same problem with it as this issue).

Steps to Reproduce

using ImageMagick;
using System;
using System.Net.Http;

MagickImageCollection imageCollection = new(await new HttpClient().GetStreamAsync("https://user-images.githubusercontent.com/77853483/122071182-d5f23000-cdf6-11eb-92fa-359fdfdb5de8.gif"), MagickFormat.Gif);
imageCollection.Write($"{AppDomain.CurrentDomain.BaseDirectory}gif.gif", MagickFormat.Gif);
imageCollection[5].Write($"{AppDomain.CurrentDomain.BaseDirectory}gif.png", MagickFormat.Png);

System Configuration

• Magick.NET version: Magick.NET-Q8-x64 7.24.1
• Environment (Operating system, version and so on): Windows 10 Home 64-bit (10.0, Build 19042) (19041.vb_release.191206-1406)
• Additional information:
  CPU: Intel Core i5-4440 3.10GHz
  GPU: GeForce GTX 1060 6GB
  GPU Drivers: 466.77

[dlemstra]

This is happening because each frame of your gif contains only the changes compared to the previous frame. You will need to call imageCollection.Coalesce before writing the image to make sure each frame contains all the pixels.

p.s. You should also need to do using MagickImageCollection imageCollection