High resolution portable biometric reader for neonates

Abstract

The invention patent describes a high-resolution portable biometric reader for newborns, according to its characteristics, a biometric reader (1) for newborns is provided, which is a curved portable electronic structure with a frame body and a comfortable handle that allows the operator to hold the reader with one hand and has an inclined capture surface that can be arranged according to the position of the newborn, thus enabling the digital capture of the newborn's fingerprints and the mother's fingerprints using the technique of frustrated total internal reflection with a prism as an optical system (4) that has a resolution greater than 29 LP / mm (1450 ppi) on the entire capture area greater than 18x36 mm, in order to fully optimize the capture process for the imaging of the newborn's fingerprints, palm prints and footprints, and the mother's fingerprints, that is, to register the fingerprints of the baby and the mother at the same time, and subsequently include them in a medical registration system to improve record tracking.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to biometric readers, and more particularly to a high resolution portable biometric reader for newborns, which, according to its characteristics and due to its basic principles, provides a biometric reader for newborns, which is specific, independent and curved portable electronic structure, and based on a frame and a comfortable handle, the operator is able to grasp the reader with one hand and arrange the capture surface area according to the position of the newborn, enabling the digital capture of the newborn's fingerprint and the mother's fingerprint using the technique of frustrated total internal reflection with a prism as an optical system, which has a resolution greater than 29 lp / mm (1450 ppi) on the entire capture area greater than 18 x 36 mm, so as to provide a global optimization in the imaging of the newborn's fingerprints, palm prints and footprints and the corresponding mother's fingerprints in the capture process in a very practical, safe and precise way, i.e., registering the fingerprints of the baby and the mother simultaneously and subsequently including these fingerprints in a medical registration system, to improve record tracking. BACKGROUND

[0002] With specific design and form and easy access for applicability and user safety, the high resolution portable biometric reader is very profitable in terms of convenient features and functionality in terms of operation, and due to its generic characteristics and dimensions, it is easily adaptable to various newborn babies, various places and general users, regardless of the characteristics they can present.

[0003] Citizen identification is the first step in citizenship, since as a citizen, a person is recognized in society with rights and responsibilities. However, registration in national identification systems is currently the weakest link. Birth certificates do not guarantee the uniqueness of the citizen, since they lack a provision that binds the file to its holder.

[0004] According to data from the United Nations, after the trade in drugs and weapons, the trade in people is the most profitable branch of organized crime, especially the trade in children and adolescents and newborn babies. Official investigations from different governments show the trafficking route.

[0005] It has now been proven that there is illegal organ trafficking in several regions of Brazil, as well as people who disguise themselves as social saviors to try to convince poor pregnant women to give their babies to them after they are born; identification requests for children found with suspicious women are very common, as well as for those whose mother's name is different in the birth certificate.

[0006] Although a system of identification of newborns is provided in the Brazilian legislation (Law No. 8069 / 90 "Children and Adolescents"), the current system of identification of newborns is outdated, thus making identification impossible and leading to the proliferation of child trafficking, organ trafficking, baby trade and ideological false crimes, since the relevant legislation does not contain provisions for proper identification of children and creation of a link of children to the information contained in the birth certificate or to the legal guardian.

[0007] The mechanism currently used to collect footprints from newborns using ink and paper is inefficient and cannot be used to collect palm prints and fingerprints, since the newborns can put their hands, which are dirty with ink, into their mouths. The quality of such collection cannot be guaranteed, since it depends on human force and proper attention to the problem cannot always be guaranteed. In addition, the resolution of the images obtained with the ink and paper collection method cannot provide sufficient detail for proper visualization of the newborn's fingerprints.

[0008] The use of the otoscopic image is more interesting than other types of biometric identification, since the otoscopic image is not invasive, making it easy and accepted, in addition to having the advantage of greater invariance, which allows its use in future identification. However, since the papillary ridge in infants is, on average, 2.5-3 times smaller than in adults and is more susceptible to deformation, the collection of this image in newborns is a difficult process.

[0009] Nowadays, commercially available biometric identification systems can only be used to identify adults. Even considering the rapid and growing development of biometric technology, there are almost no methods developed for the identification of newborns. This means that approximately 131 million newborns are born every year around the world are ignored. If we consider the world's child population between zero and five years of age (approximately 500 million), the problem is even greater.

[0010] The reality is that, despite the maturity of the technology based on fingerprints, there is no biometric identification system in the world capable of identifying newborns, i.e., the lack of such technology is a failure. The technology gap is no longer a problem; the excuse for subjecting children to vulnerability and insecurity regarding identification is no longer acceptable.

[0011] The use of biometric readers has flourished in the last few years, with several applications related to the identification of users. The readers capture fingerprint images and are coupled to software programs that identify these fingerprints and identify the individual who owns them. Examples of such readers can be found in cash machines, banks, electronic clock systems and patient registration systems.

[0012] It should be noted that, in order for the fingerprint recognition and registration system to be effective and stable, the captured images need to meet determined resolution and sharpness criteria. For example, the FBI in its legislation provides that the biometric readers certified for identification must have a minimum resolution of 500 ppi and 1000 ppi for fingerprint registration. Although sufficient to capture good images and resolve the details of an adult fingerprint, these resolution values are not accurate for a newborn, whose fingerprints and other details are significantly smaller than those of an adult.

[0013] It should also be noted that the shape of the device for capturing the fingerprints and footprints of babies is also important, since the user needs to hold the device with one hand and position it in the appropriate place, while arranging the baby's fingers, hand or foot on the contact surface in the appropriate direction and pressure for high-quality image capture. One of the most important aspects of the shape of the device is the way the user takes it, so that it is held in an appropriate and safe way, making it easier to operate and reducing the risk of falling. An optimized handle reduces the likelihood of injuries during work, such as repetitive strain injuries and work-related osteoarticular diseases.

[0014] In this act, for families and government agencies, the invention has become important to establish a link between the newborn and its mother during birth and within the delivery environment, since it would represent a big step to prevent the loss of children and help to find and identify them. In addition, this device would allow medical registration and effective treatment tracking, including vaccination programs, making better care and health for newborns.

[0015] In a broad literature review, with regard to the state of the art of biometric readers, and more specifically, with regard to the common biometric readers for newborns (object of the present invention), there is no description of the literature related to the specific object claimed in the present invention, i.e., there is no portable biometric reader that can be held with one hand and has a minimum required resolution of 1450 ppi on a minimum area of 18 x 36 mm and can be used for fingerprint imaging of newborns; however, the brief description of some of the documents in the literature and patents is a perfect explanation of the intended technical field.

[0016] Within the text of the article by Yukita, Higuchi and Jain (Progress in capturing children's fingerprints: a high-resolution CMOS image sensor with SLDR method, BIOSIG 2016, page 329), the authors describe a device capable of producing images with a resolution of 1270 ppi and show that the device is able to distinguish the peaks and valleys of a newborn's fingerprint, as in the article Figure 6The images shown are not suitable for the purpose of identification, as they are not unique. In fact, in this figure, as well as in the figures of the prior art article (Gian et al., Fingerprint recognition of infants, IEEE Transactions on Information Forensics and Security, vol. 12, p. 1501, 2017), images with porosities already appear in the third month of life, thus making it difficult to uniquely identify the child.

[0017] In the text of the patents, in the field of fingerprint biometric readers there are a large number of fingerprint biometric readers, but most of them claim the image generation method (FTIR or scattering), the optical architecture, the special components used to reduce distortion and the films used to improve the image quality. However, in all the found patent literature there is no reference to the application and the requirements for generating a proper image of an infant's fingerprint, i.e. resolution greater than 1450 ppi on an area greater than 18x36 mm (minimum area for palm print imaging and footprint area with more information), portability and usability.

[0018] In addition to the fact that none of these patents claims a handle, there is no claim to a device with a compact structure, clean and easy to assemble, designed for optimal production process, with an ideal handle for ergonomic aspects and focused on optimal user experience (biometric collector and collected agent), i.e. designed with high on-board technology that allows easy adaptation to various hospitals and pregnant families.

[0019] In the specific case of the US patent document US20050169506, a portable and lightweight device for large-format fingerprints has been described, which involves capturing four or more fingers of an adult in the case of a capture surface greater than 3x3", which is much larger than the capture surface required for an infant's fingerprint, and there is no discussion of resolution. SUMMARY

[0020] The purpose of the present invention, i.e. the overall design of the high-resolution portable biometric reader for newborns of the present invention, is based entirely on its simple and robust structure, with the minimum number of components required and very simple, safe and optimized operation, combined with quite practical manufacturing and maintenance procedures, in order to produce, through a frame and an optical system, a practical and effective biometric reader for newborns for the imaging of the fingerprints of newborns, which can be gripped with one hand, which has a transparent surface for capturing images of the fingers, hands or feet of newborns, which has a minimum required resolution of 29 lp / mm (1450 ppi) on the entire minimum capture area of 18x36 mm organized in the core of the frame.

[0021] More specifically, the biometric reader for newborns allows to simultaneously enroll the fingerprints of the baby and the fingerprints of the mother, in order to ensure the link between the newborn and the mother still in the delivery room from the first minute of its birth, through the biometric identification of the ten fingers, palm prints and footprints of the baby and the biometric identification of the ten fingers of the mother. Therefore, said biometric identification and link ensure the generation of the identification documents of the baby, such as birth certificates, civil registry, passports, etc., and control the physical visitation rights of the mother, thus ensuring that the baby is not kidnapped or trafficked, and helping to find and identify missing babies and children.

[0022] It should be noted that the biometric reader for newborns is designed with a curved shape to better adapt to the human body, presenting ideal dimensions in order to be handled roughly and continuously by doctors and nurses alike, thus avoiding work-related musculoskeletal disorders (DORT). In addition, due to the inclined capture surface, the biometric data is easier to read, which allows the device to be placed directly in the ideal position by the doctors and nurses, depending on the baby's position.

[0023] The patent of the present invention is based on several requirements of the nature of the application components and processes that meet the needs of its use, namely, the imaging of the fingerprints, palm prints and footprints of the newborn (baby). Due to the excellent quality of the synthesis of the technology, this concept ensures that the biometric reader for newborns has high efficiency, functionality, strength, durability, security, versatility, accuracy, economy, which offers advantages and improvements in the imaging of the fingerprints, palm prints and footprints of the newborn (baby) and the corresponding mother's fingerprints, and whose overall features are different from other shapes and models widely known in the current technology in the field.

[0024] The patent of the present invention comprises the use of a modern, efficient, safe and functional high-resolution portable biometric reader for newborns, formed by a set of properly combined electronic and biometric solutions, thus forming a complete and distinguished biometric reader for newborns with a unique design, refined details and specific features, which combines its own specific and proper electronic structure with high durability and strength, ergonomic shape and includes: a frame as a structural element and a comfortable handle that can be grasped with one hand, properly integrated and symmetrically arranged between each other; and a core as a storage element of the optical and optoelectronic components for fingerprint imaging, so that a single, complete and secure assembly can be formed, the shape of which, as well as the internal and external arrangement, enables to be seamless and suitable for several different types of operators, newborns and mothers, and is specifically designed for these purposes.

[0025] The biometric reader for neonates of the present invention is based on the application of components and methods of different design, however, without high complexity and sophistication, thus making it possible to solve some of the main drawbacks of other shapes and models known in the state of the art and employed in the procedures of imaging of the fingerprints, palmprints and footprints of neonates (infants), which have limitations in use and application in the range of operation, low efficiency and low performance, frequent accidents of different severity are very common, which are based on simple suitability, thus generating the drawbacks of high insecurity, great wear and fragility, low durability and strength, low versatility, high inaccuracy, laborious application, non-ergonomic, low efficiency and low performance or which have a large size, thus resulting in high cost, generally bulky and heavy, little flexibility, high maintenance, waste of a large amount of time and complex manufacturing processes. BRIEF DESCRIPTION OF DRAWINGS

[0026] The objects, advantages and other important features of the present invention can be more readily understood when considered in connection with the following drawings in which:

[0027] Figure 1A is a perspective view of a high resolution portable biometric reader for neonates.

[0028] Figure 1B is a top view of a high resolution portable biometric reader for neonates.

[0029] Figure 1C is a bottom view of a high resolution portable biometric reader for neonates.

[0030] Figure 1D is a right view of a high resolution portable biometric reader for neonates.

[0031] Figure 1E is a left view of a high resolution portable biometric reader for neonates.

[0032] Figure 1F is a front view of a high resolution portable biometric reader for neonates.

[0033] Figure 1G is a rear view of a high resolution portable biometric reader for neonates.

[0034] Figure 2A is a side view cross-section of a high resolution portable biometric reader for neonates.

[0035] Figure 2B is a top view cross-section of a high resolution portable biometric reader for neonates.

[0036] Figure 3is a schematic of a high resolution portable biometric reader for neonates showing the finger application on the prism.

[0037] Figure 4 is a perspective view of a fingerprint in a high resolution portable biometric reader for neonates.

[0038] Figure 5A is a chart of the size of the capture area of a high resolution portable biometric reader for neonates testing the relationship of the length of the field of view versus the magnification of the surface (on which the finger is placed) as a function of the total magnification in the compression direction produced by the prism in the image.

[0039] Figure 5B is a chart of the system resolution in the capture area of a high resolution portable biometric reader for neonates testing the relationship of the system resolution versus the magnification as a function of the total magnification in the compression direction produced by the prism in the image.

[0040] Figure 6 is an image of the NBS 1963A test target at the edge of the prism with a total magnification in the compression direction of 0.17: A - top left corner, B - top right corner, C - bottom left corner, D - bottom right corner. DETAILED DESCRIPTION

[0041] As shown in the figures that show and integrate the present descriptive report of the patent "High resolution portable biometric reader for neonates", figure (1A) shows a biometric reader that in general comprises a complete and with specific characteristics biometric reader for neonates (1) that incorporates itself appropriate and specific portable electronic structure with high durability and strength, internal and external shape in ergonomic shape and arrangement suitable for various types of operators, neonates and mothers, and that comprises a frame and a comfortable handle (2) appropriately integrated and arranged symmetrically between each other and a core (3) for optical and optoelectronic components to be used for the imaging of the fingerprints, palm prints and footprints of the neonates and the imaging of the fingerprints of the mothers with a method of frustrated total internal reflection through an optical system (4) with a prism with a resolution greater than 29 lp / mm (1450 ppi) on the entire capture area and greater than 18 x 36 mm, the device being connected to a palm computer for the processing, storage and transmission of the images.

[0042] The frame and handle (2) comprises: a V-shaped upper recess (2A) disposed along the entire length of the upper surface of the frame (2); a horizontal U-shaped upper recess (2B) horizontally parallel and symmetrically centered in the upper rear portion of the frame (2); a straight front edge (2C) obliquely and symmetrically disposed along the entire length of the front surface of the frame (2); a convex rear curve (2D) symmetrically disposed around the lower rear portion of the frame (2); two concave side recesses (2E) vertically and parallelly disposed along the entire length of the side surfaces of the frame (2); and a concave lower recess (2F) disposed along the lower rear portion of the frame (2).

[0043] Figure 3 The optical system (4) shown comprises: a right triangle glass prism (4A) vertically, parallelly and symmetrically disposed along the entire length of the rear surface of the frame and handle (2); a green LED panel (4B) having a parallelepiped shape and disposed horizontally, parallelly and symmetrically below (in front of the cathetus) and along the entire length of the lower surface of the right triangle glass prism (4A); an internal lens (4C) having a focal length of 25 mm, a maximum size of 2 / 3", a minimum working distance of 100 mm, an axial resolution of 200 lp / mm and an edge resolution of 160 lp / mm and vertically, parallelly and symmetrically spaced apart from the rear surface of the right triangle glass prism (4A); and an image sensor (4D) vertically, parallelly and symmetrically spaced apart from the rear surface of the internal lens (4C).

[0044] The right triangle glass prism (4A) is illuminated by the green LED panel (4B) disposed near the cathetus of the right triangle glass prism (4A). The light emitted by the green LED panel (4B) undergoes total internal reflection in the hypotenuse surface of the right triangle glass prism (4A). When a finger contacts this surface, assuming the refractive index of the fingerprint peak is close to that of the right triangle glass prism (4A), the fingerprint peak suppresses the total internal reflection and the incident light rays on these points are no longer reflected by the right triangle glass prism (4A). The light rays reflected by the right triangle glass prism (4A) are captured by the internal lens (4C) and imaged by the optical image sensor (4D).

[0045] More specifically, the optical system uses a right triangle glass prism (4A) of ninety degrees, the generated image is compressed in the direction of the cathetus of the right triangle glass prism (4A), i.e. a magnification of 0.707 is introduced in this direction. Therefore, the total magnification of the optical system will be 0.707 times the internal lens (4C) magnification in the direction of the compressed image and equal to the internal lens (4C) magnification in the direction without compression.

[0046] The high resolution portable biometric reader for neonates is image based, regardless of the method used as optical system, i.e. it encompasses the method of frustrated internal reflection, the method of scattering, the combination of the two preceding methods, the prism reader or the non-prism reader, even the direct imaging without the use of lenses.

[0047] The resolution greater than 29 lp / mm (1450 ppi) over the entire capture area refers to the resolution in the object plane, i.e. in the transparent surface on which the fingers, hands and feet of the neonate and the fingers of the mother are placed. The resolution in the image plane, i.e. in the image sensor (R image ) is equal to the resolution in the object plane (R object ) divided by the magnification of the optical system (M), according to the present invention, the resolution in the object plane (R object ) is greater than 29 lp / mm and the magnification M is equal to the sensor size divided by the object size, where the object size corresponds to the size of the fingerprint capture area in the transparent surface on which the fingers, hands and feet of the neonate and the fingers of the mother are placed. Possibly, based on the size of the hands of the neonate published by Honoré, Lakza and Druelet in the article (measurement data from the hands of human infants born from about 26 to 41 weeks of gestational age, published in the summary data of volume 7, page 1451 in 2016), it is estimated that a capture area large enough to image not only the fingerprints of the baby, but also the palm prints and footprints of the baby and the fingerprints of the mother, indicates a width usually less than 36 mm.

[0048] The requirement posed by the equation in the image sensor resolution (R image ) involves the complete optical system and, in order to meet this requirement, all the optical system components need to have a resolution greater than or equal to the requirement, i.e. they need to have a resolution or MTF (Modulation Transfer Function) greater than R object / M. It is important to observe that the optical architecture using prisms can present different magnifications for the image height and width and the corresponding resolutions. In this case, both dimensions must meet the requirement posed by the equation in the image sensor resolution (R image ).

[0049] The magnification value is the value of the magnification for the image capture, where the equation of the optical system magnification (M) calculates a width of 36 mm on the side with the larger size (sensor width). It is important to observe that the magnification value and the resolution value are values resulting from the combination of all the optical elements in the system, which can include lenses, prisms and filters. The sensor with the larger size needs an optical system with a smaller resolution, but also a lens with a larger image circle.

[0050] The operation of the high-resolution portable biometric reader for newborns is based on a process of fingerprint registration of the mother, which can be carried out as early as the prenatal stage or on the day the mother goes to the hospital to give birth. According to the biometric registration of the mother, the registration of the newborn is carried out as follows: immediately after the umbilical cord is cut and the first vital signs procedure of the baby is determined in the delivery room, the professional responsible for collecting the data cleans the baby's palms and feet and starts the fingerprint, palmprint and footprint imaging procedure using the biometric reader for newborns. A specific computer program analyzes the quality of the images in real time and automatically saves the data with acceptable quality, linking the biometric to the biometric of the mother and the number of the birth certificate. This information is stored in a database that is automatically communicated with the identity registration agency, and all the data collected is sent for the purposes of storage, verification, confirmation and identification. The maternity hospital or hospital, in turn, can help to establish contact between the newborn and the mother separated from it through a computer program.

[0051] As a test for the biometric reader for newborns, by using the NBS 1963A test target, the resolution of the captured image was measured in the prism surface where the fingerprint was placed, the object plane resolution in the center of the prism (the position where the finger was placed) corresponding to the total magnification in the compression direction, so that the magnification was less than 0.17, the resolution in the compression direction was greater than 36 lp / mm, this value being higher than the minimum required value of 29 lp / mm, since the resolution of the lens used in the central area is greater than 200 lp / mm, this value is higher than the minimum value of 170 lp / mm previously determined.

[0052] When the specification of the lens resolution on the edge of the lens used was reduced to 160 lp / mm, the resolution on the edge of the prism was also measured, where the resolution in the compression direction was reduced to 29 lp / mm, thus satisfying the conditions required in the patent of the present invention.

[0053] Since the high-resolution portable biometric reader for newborns has completely integrated components, it can be quickly assembled and disassembled, does not loosen or come off and achieves high performance and efficiency, with high durability and overall safety during use. Once completely integrated, the components are completely locked and joined, preventing them from loosening during use, so that this assembly is completely usable in the delivery room for the process of fingerprint, palmprint and footprint imaging of the newborn (baby) and of the corresponding mother. Therefore, the biometric reader for newborns (1) can be used without involving any nature, mainly regarding the safety and durability of its components, as well as the safety of its users (operators, mothers and newborns).

[0054] The high-resolution portable biometric reader for newborns is characterized by the following specific advantages: full portability allowing to take the high-resolution portable biometric reader to the mother's bed and to the baby's crib; high ergonomics with shape and weight allowing the operator to grasp and operate with one hand in a comfortable and safe way, leaving the operator's other hand free to hold and position properly the baby's fingers, hand or foot; high resolution on the whole capture area capable of imaging a newborn's fingerprint significantly smaller than an adult's; capture area large enough to capture images of significant portions of the baby's hand and foot to allow their identification; and hygienic surfaces allowing to clean and disinfect the reader surfaces in contact with the baby and the mother between uses.

[0055] In view of the above, the biometric reader will be universally accepted by the parents of newborns, hospitals, government health and safety agencies, because the high-resolution portable biometric reader for newborns has many advantages, such as: very safe, reliable and flexible in its application; high efficiency and high performance in its application due to its general concept; very comfortable, convenient and safe for the user; high overall strength and durability, combined with overall low or no wear of the components; fully acceptable costs providing the best cost-benefit ratio; practical and safe use by any user; high range; very low and practical general maintenance; perfect and direct adaptation to different types of newborns in general; high operating precision; fully compatible general weight and size; high ergonomics; full hygiene; seamless integration with computer systems; and of course the biometric reader for newborns fully complies with the current rules and regulations required for its application.

[0056] All these properties classify the high-resolution portable biometric reader for newborns as a fully general, effective, practical and safe way of applying in the fingerprint imaging process of a number of different types of fingerprints, palm prints, footprints and those of the corresponding mothers of a large number of newborns (babies) in most different types of environments and users, regardless of the general characteristics they can have. It is also easy to use and operate, combining very good performance and excellent general characteristics; however, the size and number can vary according to the general needs of each application.

Claims

1. A high-resolution portable biometric reader for newborns, the high-resolution portable biometric reader for newborns comprising a newborn biometric reader (1) incorporating a portable electronic structure having an ergonomic shape and including an integrated and symmetrically arranged frame and handle (2) and a core (3) for optical and optoelectronic components, for acquiring images of a newborn's fingerprints, palm prints, and footprints and an image of the mother's fingerprints via an optical system (4) using suppressed total internal reflection of a prism, the prism having a resolution greater than 29 lp / mm over the entire capture area, and the capture area being greater than 18 × 36 mm, the newborn biometric reader (1) being interconnected with a handheld computer for processing, storing, and transmitting images, characterized in that, The frame and handle (2) include: a V-shaped upper recess (2A) arranged along the entire length of the upper surface of the frame and handle (2); a horizontal U-shaped upper recess (2B) arranged horizontally, parallel and symmetrically in the upper rear portion of the frame and handle (2); a straight front edge (2C) arranged obliquely and symmetrically along the entire length of the front surface of the frame and handle (2); a convex rear curved surface (2D) arranged symmetrically around the lower rear surface of the frame and handle (2); two concave side recesses (2E) arranged vertically and parallel along the entire length of the side surfaces of the frame and handle (2); and a concave lower recess (2F). The optical system (4) is arranged along the lower rear surface of the frame and handle (2); and the optical system (4) comprises: a right-angled triangular glass prism (4A) arranged vertically, parallelly and symmetrically along the entire length of the front surface of the frame and handle (2); a green LED panel (4B) having a parallelepiped shape and arranged horizontally, parallelly and symmetrically along the entire length of the lower surface of the right-angled triangular glass prism (4A), i.e., in front of the right-angled side; an internal lens (4C) having a focal length of 25 mm, a maximum size of 2 / 3'', a minimum working distance of 100 mm, an axial resolution of 200 lp / mm and an edge resolution of 160 lp / mm, and the internal lens being vertically, parallelly and symmetrically spaced from the rear surface of the right-angled triangular glass prism (4A); and an image sensor (4D) being vertically, horizontally and symmetrically spaced from the rear surface of the internal lens (4C).

Images