Multi picture object
Multi Picture Object (MPO) or Multi Picture Format (MPF) is an image format for three-dimensional photography.
Classic image formats such as JPEG or PNG, which are established in two-dimensional photography, are not suitable for storing stereoscopic images - there is only space for one photograph in each file, but at least two photographs are required, one for the right and one for the left eye.
In the Multi Picture Object format , all the data required for display are saved in a single file with the .MPO extension in order to make it easier for the user to handle the stereoscopic image material. It would be possible to save both photographs in separate files in one of the formats mentioned, but it can be problematic if one of the two files is accidentally deleted or incorrectly saved in a different location and can no longer be found by the viewing software .
Origin and structure of the format
The MPO format was standardized by the CIPA ( Camera & Imaging Products Association ) in 2009 and is now the standard output and input format for three-dimensional photographs in the devices of several manufacturers. The MPO standard is based on the JFIF standard , which in turn describes a container format for JPEG files.
Not only the structure of an MPO file is based on the well-known: The JPEG process is used for the compressed storage of the images within an MPO file Additional information necessary for the three-dimensional representation.
MPO as an extension of JFIF
The expandability that the JFIF standard provides via the APPx markers is used by the MPO format to enable the organized storage of multiple images within a single file. In order to avoid conflicts with the frequently used Exif and IPTC markers APP1 and APP13, the data of the MPO extension is saved in the APP2 marker.
An MPO file consists of a simple concatenation of two or more JPEG files in JFIF containers. The images are linked together and stored in a single file. The only difference between a single image in this concatenation and a conventional JPEG file is the lack of the APP0 marker with the JFIF version information and the presence of the APP2 marker and the information it contains to represent the concatenated images. Usually, the images in an MPO file also contain the APP1 marker with Exif metadata and a thumbnail of the image.
The APP2 marker contains a few bytes to identify the marker as an MPO extension, version information on the MPO specification used, a number of parameters that describe the viewing angle and the exact position of the recording, as well as a type assignment for the respective image. The type describes, to a certain extent, the content of the particular image and determines how it should be displayed. Valid types are:
- (A) Baseline MP Primary Image (primary image), ...
- (B) Large Thumbnail (version in different resolution), ...
- (C) Multi-Frame Image (different view of the scene) and ...
- (D) Undefined (undefined type).
In the APP2 marker, the first image in the chain also contains an index of all images contained in the MPO file, each with individual identifiers, image dimensions (height times width), the exact position in the file and the size of the respective image within the file in Byte. This index is used to be able to individually access all images within the file.
Possibilities of the format
While the storage and display of stereoscopic images is a common use for the MPO format, MPO can do more. It is possible to save more than just two individual images within the file and these images do not necessarily have to represent different views of the same scene at the same point in time.
Baseline MPO mode
The structure of the MPO extensions in the APP2 marker makes it possible to display a scene from different perspectives at a given point in time, but in fact one of the original uses of the format was to save two variants of the same image: a variant in the original resolution , a variant in a resolution optimized for display on HD TVs. This form of use is also called the Baseline MPO mode, it is the only valid type that allows A (primary image) and B (version in a different resolution).
Extended MPO mode
The Extended MPO mode is used far more frequently than the Baseline MPO mode in practice . This allows all types and, thanks to the undefined type, leaves the creator practically all freedom when composing the linked images. Although a complete slide show (think of a set of vacation pictures) would be practically possible within a single file, this use is rather rare. In conventional usage, an MPO file contains several views of the same scene, i.e. images of type C (different view of the scene). For type C, three sub-types are defined in the MPO standard: Panorama , Disparity and Multi-Angle .
Panorama mode
The panorama sub-type is largely self-explanatory and easy to distinguish from the other sub-types: all images of this sub-type within an MPO file together result in a comprehensive view of a scene (e.g. interior view of a historical building) from a specific location. The images were photographed in such a way that they can be put together seamlessly at the edges, thus creating the illusion of an actual all-round view for the viewer .
Disparity mode
The distinction between the sub-types disparity and multi-angle is less easy . Both types are used for images that show a certain scene from different locations and possibly slightly or very different angles. The difference between the types lies in the intended display mode: In the case of images of the disparity type , the locations of the individual images differ only slightly from one another, as small as the typical distance between two human eyes. The disparity type is used for images that are intended for simultaneous, three-dimensional viewing on 3D-enabled devices. It is possible to store more than just two images of the type disparity in the chain, and thus to store several three-dimensional views of a scene in a single file.
Multi-angle mode
On the other hand, images of the 'multi-angle' type are usually not suitable for simultaneous, three-dimensional viewing. The individual pictures of this type show different, sometimes very different views of a scene and are intended for individual viewing. With pictures of this type, a view of a historical building from the north, east, south, west or even from a bird's eye view is conceivable.
JPS as an alternative to MPO
JPEG Stereoscopic (JPS) is another image format that is suitable for storing and displaying stereoscopic images. Like the MPO format, it is based on the JPEG method and the JFIF container, but offers far fewer options than MPO and is less common in practice.
In contrast to an MPO file, a JPS file consists of a single JPEG / JFIF file. The extensions for the three-dimensional display as well as the identification as JPS file are saved in the previously unused APP3 marker. The two views of the image for stereoscopic display are stored side by side within a single image. JPS files, like normal JPG files, usually contain the APP0 marker with the JFIF version information, unlike the linked images within an MPO file.
The special type of storage within a JPS file has a major advantage over storage within an MPO file: The only difference to a conventional JPEG file is the APP3 marker, which is ignored by display programs that are not compatible with JPS. Therefore, both views can be displayed within any conventional JPEG-capable viewer. MPO also offers such an option for display on incompatible platforms, but only for the first image in the chain.
Individual evidence
- ↑ Multi-Picture Format Specification of the CIPA ( Memento of the original from April 5, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF 1.2 MB)
- ↑ http://www.burosch.de/technik/355-multi-picture-object-mpo-3d-bildformat.html
