Adding New IptcProfile to PNG file

[markolbert]

This code successfully adds keywords to an existing IptcProfile in a jpg file, but fails to add keywords to a PNG file which doesn't already contain an IptcProfile.

using var image = await Image.LoadAsync( filePath, ctx );

image.Metadata.IptcProfile ??= new IptcProfile();

// ensure we're case-insensitive
var toAdd = new HashSet<string>( keywords, StringComparer.OrdinalIgnoreCase );

// add the existing keywords to what we're going to add if we're
// appending, and then remove all the existing keywords from the
// profile so we don't create duplicates
if( appendKeywords )
{
    toAdd.UnionWith( image.Metadata.IptcProfile.Values.Where( v => v.Tag == IptcTag.Keywords )
                          .Select( v => v.Value ) );
}

image.Metadata.IptcProfile.RemoveValue( IptcTag.Keywords );

foreach( var keyword in toAdd )
{
    image.Metadata.IptcProfile.SetValue( IptcTag.Keywords, keyword );
}

await image.SaveAsync(filePath, ctx);

Is there some additional initialization that needs to be done on a new IptcProfile?

[JimBobSquarePants]

I’ll have a look. The process code should be the same.

[markolbert]

I've been wandering through a cloned version of ImageSharp in my solution and think I may have learned some things that bear on this question.

The IptcProfile property of the ImageMetadata class appears to only be set for JPG files (the logic is part of the JpegDecoderCore class). I've seen this in action when dealing with JPG files in my app...and if it never gets initialized for other image types, that would explain part of what I'm seeing.

I also noticed the Encode() method in PngEncoderCore does not have a call to store Iptc data:

this.WriteHeaderChunk(stream);
this.WriteGammaChunk(stream);
this.WriteCicpChunk(stream, metadata);
this.WriteColorProfileChunk(stream, metadata);
this.WritePaletteChunk(stream, quantized);
this.WriteTransparencyChunk(stream, pngMetadata);
this.WritePhysicalChunk(stream, metadata);
this.WriteExifChunk(stream, metadata);
this.WriteXmpChunk(stream, metadata);
this.WriteTextChunks(stream, pngMetadata);

but it does reference WriteTextChunks(). Is it possible to store the Iptc subject data in the pngMetadata and have that show up as Iptc metadata?

[JimBobSquarePants]

Yes. PNG doesn't support it.... yet. However, I am writing support for decoding and encoding the information right now.

In my research I discovered this snippet

https://dev.exiv2.org/projects/exiv2/wiki/The_Metadata_in_PNG_files

There are no standard for Exif, IPTC data. In Exiv2, when Exif, IPTC are added, they are stored in zTXt text chunks and save as ASCII.

I think ImageSharp will probably do the same. I'm fairly certain Magick.NET does also.

Btw do you have any PNG files containing IPTC data I could test the decoder with?

[markolbert]

Here's a png file with Xmp and Iptc metadata (courtesy of MagickNET :)).

[markolbert]

Thanx for adding the new encoder/decoder!

[JimBobSquarePants]

No worries! See #3048 for the details.