Resize from large source to small thumbnail produces deformed top pixel rows

[patrikwlund]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of ImageSharp
• I have verified if the problem exist in both DEBUG and RELEASE mode
• I have searched open and closed issues to ensure it has not already been reported

Description

Downsizing a large image can cause oddly sampled pixels in the top rows of pixels (I only noticed it in the top rows at least).

I tested multiple samplers. All of them displayed similar results.

Steps to Reproduce

using (var image = Image.Load(flowersJpg))
{
    image.Mutate(i => i.Resize(new ResizeOptions
    {
        Size = new Size(300, 300),
        Mode = ResizeMode.Crop
    }));

    image.SaveAsJpeg(outputStream);
}

System Configuration

• ImageSharp version: 1.0.0-beta0007
• Other ImageSharp packages and versions:
• Environment (Operating system, version and so on): Windows 10 (1903)
• .NET Framework version: 4.7.1
• Additional information:

Source Image

Example results

Resized with ImageSharp

Resized with ImageResizer

[scleaver]

I am seeing the same issue in my site which is using ImageSharp but not always when dropping to a small image.

https://www.kast.io/media/concepts/group-ideas.jpg?width=1920&height=832&rmode=crop
https://demo.kast.io/media/groups-demo/family-groups2.jpg?width=408&height=316&rmode=crop

[JimBobSquarePants]

@scleaver Can you include the source images directly in this issue please, Just in case they get removed or updated on your servers. Thanks!

[scleaver]

I think the issue is caused by the size of the source image.

[JimBobSquarePants]

Thanks @scleaver

@antonfirsov one for you I think. Let me know if you need a second pair of eyes.

[netwavebe]

I'm having the same issue. This is the top (zoomed in) of a 1980x5520 jpeg cropped to 480x600:

I can provide the original image if needed.

[JimBobSquarePants]

@netwavebe Please do. Thanks!

[netwavebe]

Original image is 1980 x 5520:

This image cropped to 480 x 600:

The top distortion is probably very visible here because we're cropping a lot in this image...

[JimBobSquarePants]

@netwavebe I'm assuming you're simply passing the new width and height with ResizeMode.Crop yeah?

[netwavebe]

@JimBobSquarePants Yes, exactly!