How to include metadata in an image file generated from a base64 string using JavaScript

I need to enhance my existing base64 string to image file conversion code by adding metadata such as last modified date, photographer, copyright, and credits. However, the initial attempt below did not yield the desired results. Is there a better way to incorporate this metadata?

In the code snippet provided, the variable `base64Source` represents the dataUri containing the base64 content.

function updateImageMetadata(base64Source, name) {
        var base64Content = base64Source.substr(base64Source.indexOf(',') + 1);

        var byteString = window.atob(base64Content);
        var ia = new Uint8Array(byteString.length);
        for (var i = 0; i < byteString.length; i++) {
            ia[i] = byteString.charCodeAt(i);
        }

        var file = new Blob([ia], {type: 'image/jpeg'});
        return new File([the_file], name);
    };

I have attempted modifying the code as shown below:

function updateImageMetadata(base64Source, name) {
        var base64Content = base64Source.substr(base64Source.indexOf(',') + 1);

        var byteString = window.atob(base64Content);
        var ia = new Uint8Array(byteString.length);
        for (var i = 0; i < byteString.length; i++) {
            ia[i] = byteString.charCodeAt(i);
        }

        var file = new Blob([ia], {type: 'image/jpeg'});
        return new File([the_file], name,{
            lastModified: new Date().getTime(), 
            tooltip : 'test tooltip',
            caption : 'test caption',
            copyright : 'Test',
            credits : 'Test'
        });
    };

Answer №1

Including metadata in the file's data itself is essential for proper organization.

Despite the limitations of the javascript File object in modifying file data, certain options like EOL endings from the Blob constructor can be inherited.

To make changes to your file's data, you'll need to directly modify the bytes within the ia's ArrayBuffer.

The process of adding metadata varies depending on the type of image format being used. Different formats have specific rules for accepting and storing metadata within the file structure.

For example, JPEG files, TIFF, and webp formats commonly store metadata in EXIF data within an Application Segment identified by a 0xFFE1 marker for JPEG. Webp uses a chunkHeader('EXIF') to mark metadata, while also supporting XMP. PNG files allow text-info metadata as well.

Various file formats may support different metadata structures, making it challenging to create a universal encoder for all. Fortunately, libraries are available for popular formats like JPEG's EXIF metadata, which can be easily found through online searches.

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