Native Image Format Metadata Queries

This topic provides an overview of the metadata query language queries for reading and writing metadata supported by GIF, PNG, TIFF and Jpeg images.

This topic contains the following sections.

• Prerequisites
• Introduction
• GIF Metadata
• PNG Metadata
• TIFF Metadata
• Jpeg Metadata
• Related topics

Prerequisites

To understand this topic, you should be familiar with the Windows Imaging Component (WIC) metadata system as described in the WIC Metadata Overview. You should also be familiar with the query language used to read and write metadata, as described in Metadata Query Language Overview.

Introduction

The following sections contain tables that list the available metadata queries for each image file type. Each table has the following columns:

• Path - The query path used to retrieve the metadata item.
• Name - The name of the metadata item.
• Type - The type of the metadata item retrieved from the query path.

The query paths are used by the WIC metadata API to access the embedded metadata of an image. The following example code demonstrates using an IWICMetadataQueryReader to query for a JPEG's IFD metadata block.

// Not shown: image decoding 
IWICMetadataQueryReader *pQueryReader = NULL;
IWICMetadataQueryReader *pIFDReader = NULL;

// Get the query reader.
if (SUCCEEDED(hr))
{
    hr = pFrameDecode->GetMetadataQueryReader(&pQueryReader);
}

if (SUCCEEDED(hr))
{
    // Get the nested IFD reader.
    hr = pQueryReader->GetMetadataByName(L"/app1/ifd", &value);
    if (value.vt == VT_UNKNOWN)
    {
        hr = value.punkVal->QueryInterface(IID_IWICMetadataQueryReader, (void **)&pIFDReader);
    }
    PropVariantClear(&value); // Clear value for new query.
}

GIF Metadata

The Graphics Interchange Format (GIF) image format supports both global and frame level metadata. The following two sections provide the metadata query paths available for GIF's global and frame level metadata.

Global Metadata

The following table provides the available metadata query paths that can be used to access global GIF metadata.

Frame Metadata

The following table provides the available metadata query paths that can be used to access frame level GIF metadata.

PNG Metadata

The Portable Network Graphics (PNG) image format supports frame level metadata.

Frame Metadata

The following table provides the available metadata query paths that can be used to access frame level PNG metadata.

For details about PNG

TIFF Metadata

The Tagged Image File Format (TIFF) image format supports frame level metadata.

Frame Metadata

The following table provides the available metadata query paths that can be used to access frame level TIFF metadata.

Jpeg Metadata

The JPEG image format supports frame level metadata.

Frame Metadata

The following table provides the available metadata query paths that can be used to access frame level JPEG metadata.

Related topics

Conceptual

Windows Imaging Component Overview

WIC Metadata Overview

Metadata Query Language Overview

Metadata Extensibility Overview

How-to: Re-encode a JPEG Image with Metadata

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Build date: 3/14/2012