ISO IEC 19794-9:2011 pdf – Information technology一Biometric data interchange formats一 Part 9: Vascular image data.
6.1 Byte and bit ordering
The quantities in all records and vascular biometric image elements (p.xel data), ii represented as multibyte quantities, are represented in big-endian format. That is. the more significant bytes of any inultibyte quantity are stored at lower addresses in memory than are the less significant bytes. The order for transmission shall also be the most significant byte first and the least significant byte last. Within a byte, the order of transmission shall be the most significant bit first and the least significant bit last. All numeric values are unsigned integer quantities of fixed-length.
6.2 Scan sequence
A raw vascular image data conforming to this part of ISO/IEC 19794 is a two dimensional bit-mapped data that scans an object from the upper left corner to the lower right corner within a region of interest of a human body. This standard defines the scan direction of an imaging sensor as being along the positive x and y-axis which is defined in clause 7.9 for each vascular biometric tedndogy, assuming the target human body (finger, back of the hand, or palm, etc.) is positioned In standard pose. The standard pose is defined n dause 7.8. If an image is scanned in a standard pose, the x and y-axis of the object coordinate system is in parallel with the x and y.axis of the image coordinate system. The x-direction of the image coordinate system is defined as the scan line from left to right and the y-dlrection as being from the top to the bottom of the image. Additionally. in a standard pose, the object z-axis is assumed to be in a direction parallel with the z.axis of the imaging device.
The scan sequence shall be raster scan order that Is. image pixels are acquired along the x-axis from lop to bottom in the y-direction. In order to map the object coordinate system to the image coordinate system without further translahon, each vascular biometric image data may define the x and y.axis origin which is not the pixel location of the upper-left corner of the image. If the origin is not specifically defined, it shall be the pixel location of the upper-left corner of the image.
7 Image capture requirements
7.1 Spatial sampling rate
Image capture requirements are dependent on various factors such as the type of application, the available amount of raw pixel information to be retained or exchanged, and the targeted performance. Another factor to consider as a requirement for vascular biometric imaging is that the physical size of the target body area where an application captures an image for the extraction of vascular pattern data vanes substantially (unlike other biometric modalities). For example, a finger vein biometric device may require higher spatial sampling rate than a palm vein device due to difference size of the observed biometric characteristic. Therefore, this standard does not specify the requirement of minimum spatial sampling rate. However, the spatial sampling rate of the captured image shall be represented in terms of pixels per centimetre.
7.2 Bit.depth
The image shall have a dynamic range spanning at least 128 gray scale levels, allocating at least one byte (8 bits) per intensity value and providing at least 7 bits of useful intensity information. The image may utilize two or more bytes per gray scale value instead of one.
7.3 Illumination
For the capture of vascular biometric images, the skin is typically illuminated using near.infrared wavelengths in the range of approximately 700 to 1200 nm. The angle from the light source to the tangent plane of the skin’s surface is not defined in VIR because technologies that use a reflectance image may use diffuse illumination instead of direct illumination for the purpose of avoiding specular reflectance.