Square artifacts in color data on jpeg outputs

[jrdiver]

I was messing with the Resize sample just trying to figure out the library, but I keep getting some weird
block artifacts when the quality is set to less then a jpg quality of 91 on ImageSharp's NuGet package 1.0.3-Alpha.0.35

I reverted it back to the latest stable - 1.0.2 and the issue went away. Code used is basicly the sample besides removing grayscale and changing output to jpg with a quality setting.

`
System.IO.Directory.CreateDirectory("output");

        using (Image image = Image.Load("fb.jpg"))
        {
            image.Mutate(x => x.Resize(image.Width / 2, image.Height / 2));

        image.SaveAsJpeg("output/Photo.jpg", new JpegEncoder { Quality = 75 }); // Automatic encoder selected based on extension.
        }

`

System Configuration

Windows 10/Visual Studio 2019/NetCore3.1

[JimBobSquarePants]

@jrdiver This would have been better raised as a discussion. Please in future use the supplied template. It's very important that you do so.

Please, with all the required information, also supply comparison output images so that we do not have to spend time replicating your process before we can even determine whether there is an issue.

[jrdiver]

First picture is just from the samples, second is my profile picture, here's the original. I did try several other pictures and got similar results, reverting back to the latest stable "solved" the issue, but if there does seem to be something going on with the latest prerelease.

[JimBobSquarePants]

Can you please label the images so I can tell which output image is from which version.

[JimBobSquarePants]

Ok.... I've done some investigating and there's definitely an issue introduced with #1517 Thanks for bringing this to our attention.

[antonfirsov]

I can confirm this by running JpegEncoderTests and checking the output.

This is a serious bug in JpegEncoder, and also a big reliability issue with JpegEncoderTests, will open an issue soon.

@jrdiver thanks for reporting!

[JimBobSquarePants]

@antonfirsov I've opened #1549 if you want to add to that.

[antonfirsov]

Yeah, you were faster 😄

[antonfirsov]

Fixed by #1551 in 1.0.3-alpha.0.37:
https://www.myget.org/feed/sixlabors/package/nuget/SixLabors.ImageSharp

[jrdiver]

The new build seems to be working as expected with Jpg's now. Thanks!