Skip to content

PngEncoder ignores FilterMethod #2771

@melnikov77

Description

@melnikov77

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

ImageSharp version

3.1.4

Other ImageSharp packages and versions

NA

Environment (Operating system, version and so on)

NA

.NET Framework version

net8

Description

When a new PngEncoder is created with custom FilterMethod it always produces the same file size,
i.e. the FilterMethod is being ignored.

Example:

var encoder = new PngEncoder
{
    FilterMethod = PngFilterMethod.Paeth,
};

I found only one usage of this property here

if (!encoder.FilterMethod.HasValue)
{
// Specification recommends default filter method None for paletted images and Paeth for others.
this.filterMethod = this.colorType is PngColorType.Palette ? PngFilterMethod.None : PngFilterMethod.Paeth;
}

i.e. filterMethod is assigned only if encoder.FilterMethod is null,
otherwise, it is always 0 (PngFilterMethod.None).

Steps to Reproduce

    SixLabors.ImageSharp.Image img = null!;
    
    var paethFilterStream = new MemoryStream();
    img.Save(paethFilterStream, new PngEncoder
    {
        FilterMethod = PngFilterMethod.Paeth,
    });

    var noneFilterStream = new MemoryStream();
    img.Save(noneFilterStream , new PngEncoder
    {
        FilterMethod = PngFilterMethod.None,
    });

    Assert.NotEquals(paethFilterStream.Length, noneFilterStream.Length);

Images

No response

Metadata

Metadata

Assignees

No one assigned

    Type

    No type

    Projects

    No projects

    Milestone

    No milestone

    Relationships

    None yet

    Development

    No branches or pull requests

    Issue actions