Image Metadata - Revision history

Patapom at 19:46, 4 January 2012

2012-01-04T19:46:12Z

Patapom at 17:19, 4 January 2012

2012-01-04T17:19:36Z

Patapom at 15:33, 4 January 2012

2012-01-04T15:33:34Z

Patapom: Created page with '=MetaData= Metadata are data embedded within image files that give various information about the camera and the image. For example, for pictures taken by a camera, you can find o…'

2012-01-04T14:19:15Z

Created page with '=MetaData= Metadata are data embedded within image files that give various information about the camera and the image. For example, for pictures taken by a camera, you can find o…'

New page

=MetaData=
Metadata are data embedded within image files that give various information about the camera and the image. For example, for pictures taken by a camera, you can find optics aperture, exposition, camera model, time of shot, white balance, etc.

Most importantly, for the purpose of our color correction pipeline, metadata can also embed the color profile of the image. This is mainly these metadata we will be talking about.

Also, we will not focus on how to read the metadata from a particular image file type because [[Nuaj|Nuaj']] is now using [http://en.wikipedia.org/wiki/Windows_Imaging_Component WIC] to read its bitmaps and WIC provides easy access to decoded meta-data.

Sometimes, the color profile information is as simple as the RGB/White chromaticities as can be found with [[Color_Profile#Standard_Profiles|Standard Profiles]] or other simple, custom profiles. Check the [[Color_Transforms#XYZ_Matrices|Color Transforms]] page to know how to compute the RGB &lrarr; XYZ transform matrices.

You can also find gamma information tied to the profile to understand what gamma correction should apply to the input colors.

For more complex color profiling, you can sometimes find the entire ICC profile embedded as metadata. ''All you have to do'' is then decode the ICC profile and apply it to the color data to transform the colors in [[Colorimetry#CIE_XYZ|CIEXYZ]] space.

=Metadata Types=

==EXIF==
(Source: http://en.wikipedia.org/wiki/Exchangeable_image_file_format)

EXchangeable Image File format (EXIF) can be found in TIFF and JPEG but not in PNG or GIF.

When embedded in JPEG,

==XMP==
(Source: http://en.wikipedia.org/wiki/Extensible_Metadata_Platform)

Extensible Metadata Platform (XMP) is a standard, created by Adobe Systems Inc., for processing and storing standardized and proprietary information relating to the contents of a file.

Serialized XMP can be embedded into a significant number of popular file formats, without breaking their readability by non-XMP-aware applications. Embedding metadata avoids many problems that occur when metadata is stored separately.

XMP can be used in several file formats such as PDF, JPEG, JPEG 2000, JPEG XR, GIF, PNG, HTML, TIFF, Adobe Illustrator, PSD, MP3, MP4, Audio Video Interleave, WAV, RF64, Audio Interchange File Format, PostScript, Encapsulated PostScript, and proposed for DjVu. In a typical edited JPEG file, XMP information is typically included alongside Exif and IPTC Information Interchange Model data.

XMP metadata can describe a document as a whole (the "main" metadata), but can also describe parts of a document, such as pages or included images. This architecture makes it possible to retain authorship and rights information about, for example, images included in a published document. Similarly, it permits documents created from several smaller documents to retain the original metadata associated with the parts.

We can find everything we need about decoding the XMP metadata from http://www.adobe.com/products/xmp/index.html where a .

==IPTC==
(Source: http://en.wikipedia.org/wiki/IPTC_Information_Interchange_Model)

'''NOTE:''' IPTC is then mainly used for informal, human-readable text and doesn't involve color management so we will not linger on reading it. You can skip this section altogether.

The Information Interchange Model (IIM) is a file structure and set of metadata attributes that can be applied to text, images and other media types. It was developed in the early 1990s by the [http://en.wikipedia.org/wiki/International_Press_Telecommunications_Council International Press Telecommunications Council] (IPTC) to expedite the international exchange of news among newspapers and news agencies.

IIM metadata embedded in images are often referred to as "IPTC headers", and can be easily encoded and decoded by most popular photo editing software.
The Extensible Metadata Platform (XMP) has largely superseded IIM's file structure, but the IIM image attributes are defined in the IPTC Core schema for XMP and most image manipulation programs keep the XMP and non-XMP IPTC attributes synchronized.

Because of its nearly universal acceptance among photographers — even amateurs — this is by far IPTC's most widely used standard. On the other hand, the use of IIM structure and metadata for text and graphics is mainly limited to European news agencies.

In 2001, Adobe introduced "Extensible Metadata Platform" (XMP), which is an XML schema for the same types of metadata as IPTC, but is based on XML/RDF, and is therefore inherently extensible. The effort spawned a collaboration with the IPTC, eventually producing the "IPTC Core Schema for XMP", which merges the two approaches to embedded metadata. The XMP specification describes techniques for embedding metadata in JPEG, TIFF, JPEG2000, GIF, PNG, HTML, PostScript, PDF, SVG, Adobe Illustrator, and DNG files.

@@ Line 1: / Line 1: @@
 =MetaData=
-Metadata are data embedded within image files that give various information about the camera and the image. For example, for pictures taken by a camera, you can find optics aperture, exposition, camera model, time of shot, white balance, etc.
+Metadata are data embedded within image files that give various information about the camera and the image itself. For example, for pictures taken by a camera, you can find optics aperture, exposition, camera model, white balance, etc.
 Most importantly, for the purpose of our color correction pipeline, metadata can also embed the color profile of the image. This is mainly these metadata we will be talking about.
-Also, we will not focus on how to read the metadata from a particular image file type because [[Nuaj|Nuaj']] is now using [http://en.wikipedia.org/wiki/Windows_Imaging_Component WIC] to read its bitmaps and WIC provides easy access to decoded meta-data.
+Also, we will not focus on how to read the metadata from a particular image file type because [[Nuaj|Nuaj']] is now using [http://en.wikipedia.org/wiki/Windows_Imaging_Component WIC] to read its bitmaps and WIC provides easy access to decoded metadata.
-Sometimes, the color profile information is as simple as the RGB/White chromaticities as can be found with [[Color_Profile#Standard_Profiles|Standard Profiles]] or other simple, custom profiles. Check the [[Color_Transforms#XYZ_Matrices|Color Transforms]] page to know how to compute the [[Colorimetry#RGB|RGB]] &harr; [[Colorimetry#CIE_XYZ|XYZ]] transform matrices.
+Sometimes, the color profile information is as simple as the RGB/White chromaticities as can be found with [[Color_Profile#Standard_Profiles|Standard Profiles]] or other simple, custom profiles. Check the [[Color_Transforms#XYZ_Matrices|Color Transforms]] page to know how to compute the [[Colorimetry#RGB|RGB]] &harr; [[Colorimetry#CIE_XYZ|XYZ]] transform matrices from such chromaticities.
 You can also find gamma information tied to the profile to understand what gamma correction should apply to the input colors.
-For more complex color profiling, you can sometimes find the entire ICC profile embedded as metadata. ''All you have to do'' is then decode the ICC profile and apply it to the color data to transform the colors in [[Colorimetry#CIE_XYZ|CIEXYZ]] space.
+For more complex color profiling, you can sometimes find the entire ICC profile embedded as metadata. ''All you have to do'' is then decode the ICC profile and apply it to the color data to transform the colors in [[Colorimetry#CIE_XYZ|CIEXYZ]] space. We won't be expanding much on this subject as it's too large for our purpose but you can refer to the [[Color_Transforms#Custom_ICC_Profiles|Custom ICC Profiles]] section for more information.
@@ Line 50: / Line 50: @@
 We could also use the ''Light Source'' tag describing the [[Colorimetry#Illuminant|illuminant]] used for taking the snapshot (cf. pp.55-56 for a list of possible illuminants). Anwyay, this would only apply to a direct usage of non-processed photographs, which is very unlikely in a pipeline like 3D rendering.
@@ Line 67: / Line 66: @@
 We can find everything we need about decoding the XMP metadata from http://www.adobe.com/products/xmp/index.html where an open-source SDK can be downloaded.
 =Decoding=

@@ Line 7: / Line 7: @@
-Sometimes, the color profile information is as simple as the RGB/White chromaticities as can be found with [[Color_Profile#Standard_Profiles|Standard Profiles]] or other simple, custom profiles. Check the [[Color_Transforms#XYZ_Matrices|Color Transforms]] page to know how to compute the RGB &lrarr; XYZ transform matrices.
+Sometimes, the color profile information is as simple as the RGB/White chromaticities as can be found with [[Color_Profile#Standard_Profiles|Standard Profiles]] or other simple, custom profiles. Check the [[Color_Transforms#XYZ_Matrices|Color Transforms]] page to know how to compute the [[Colorimetry#RGB|RGB]] &harr; [[Colorimetry#CIE_XYZ|XYZ]] transform matrices.
 You can also find gamma information tied to the profile to understand what gamma correction should apply to the input colors.
@@ Line 67: / Line 67: @@
 We can find everything we need about decoding the XMP metadata from http://www.adobe.com/products/xmp/index.html where an open-source SDK can be downloaded.
 =Decoding=
 So, basically we need to

@@ Line 16: / Line 16: @@
 =Metadata Types=
 ==EXIF==
@@ Line 22: / Line 37: @@
 EXchangeable Image File format (EXIF) can be found in TIFF and JPEG but not in PNG or GIF.
-When embedded in JPEG,
+The EXIF is constantly maintained to keep up to date contrary to XMP that is inherently extensible due to the use of XML.
 ==XMP==
@@ Line 37: / Line 66: @@
-We can find everything we need about decoding the XMP metadata from http://www.adobe.com/products/xmp/index.html where a .
+We can find everything we need about decoding the XMP metadata from http://www.adobe.com/products/xmp/index.html where an open-source SDK can be downloaded.
-In 2001, Adobe introduced "Extensible Metadata Platform" (XMP), which is an XML schema for the same types of metadata as IPTC, but is based on XML/RDF, and is therefore inherently extensible. The effort spawned a collaboration with the IPTC, eventually producing the "IPTC Core Schema for XMP", which merges the two approaches to embedded metadata. The XMP specification describes techniques for embedding metadata in JPEG, TIFF, JPEG2000, GIF, PNG, HTML, PostScript, PDF, SVG, Adobe Illustrator, and DNG files.
+=Decoding=