ISO TS 20793:2019 download.Photography – Lenticular print for changing images – Measurements of image quality.
Lenticular printrng is a technology wherein lenticular lenses are used tD produce printed images with an illusion of depth. i.e. threedimensional (3D) eft’ect, or the ability to change or move as the image is viewed from different angle5. Lenticular prints to display changing images are built up with a lenticular lens sheet and a printed sheet that contains at leasi two images, interleaved with the same spacial frequency as the lent Icular lens sheet.
Lcnticular lenses are an array of magnifying lenses.
Widespread applications of tenticular printing are signage, display posters, business cards, multilingual message boards and packages with changing images or 3D effects.
It has been reported that the market size of lenticular prints is over 100 mIllion m2 and that the market is growing. Furthermore, the potential image qualities of lentlcular printing have dramatically improved and further improvements are expected in the future. While production of lenticular sheets with a lens frequency of too Ipi (lines per inch) is routine, products with a 200 lpl frequency are also currently available.
Although the potential Image quality of lenticular prints is high as described above, the quality of Images is not always good In the market due to various causes. e.g.. due to the misalignment of the lenticular lens and lenticular printed images. This Is a critical problem for lenticular printing.
To improve the image quality of lenticular prints, image quality measurements are essential. This document provides standard measurement methods and the specifications for the image quality of lenticular prints.
3.1.2
lentlcular print
print combined with lenticular lenses which produces printed images with an illusion oIdepth. i.e. three- dimensional (3D) effect, or the ability to change or move as the image is viewed from different angles
Note ito cnrry The detailed explanation of lenticuLar print Is provided In AanuA.
Note 2 to entry; Lentkular prints to display changing images are built up with a lenticular lens sheet and a printed sheet that contains at least two images. Interleaved with the same special frequency as the lenticular lens sheet.
3.2 Abbreviations
CIE commission internationale de l’édairage (International Commission on Illumination)
CTP computer to plate
LMD light measuring device
LPS lenticular print sample
RGB red, green, blue
4 Standard environmental conditions
4.1 Temperature and humidity
The standard environmental conditions shall be applied for the measurements of lenticular prints.
The standard environmental conditions shall be a temperature of 23 °C ± 3 C and a humidity of
50% RH ± 1S%RH.
4.2 Ambient illumination conditions
For standard dark room conditions, the ambient Illuminance at any position on the lentlcular print Is below 0,3 lx In all directions or the Illuminance shall at least be less than a level that does not Influence the measurement results.
When directional Illumination is used, standard dark room conditions shall be applied unless ttse instrumentation used is effective in suppressing background illumination.
When the sample is set in an Integrated sphere, dark room may not be required.
S Measurement conditions
5.1 General
For the measurements, the lenticutar print samples shall be illuminated with hemispherical diffuse lighting. Directional illumination can also be used when It is appropriate for simulating the use application.
The reflected light from the print sample shall be measured using a spectroradiometer.
5.2 Geometry of measurements
5.2.1 Standard conditions with hemispherical Illumination
Uniform hemispherical diffuse illumination Is generally realized by using an integrating sphere. The lenticular print sample (LI’S) shall be placed irs the centre of an integrating sphere as shown in Figure 1.
5.5 Working standards and references
The LMI) shall be calibrated wtth a diffuse white reflectance standard sample with a diffuse reflectance of 911% or more. The reflectance shall be calculated based on the reflectance of the perfect white panel and the black panel.
Diffuse white reflectance standard samples can be obtained with a diffuse reflectance 0198% or more. They are also available In different shades olgrey, A luminance L1d measurement from such reflectance standards can be used to determine the Illuminance Eon the standard for a defined detection geometry and illumination spectra and conhiguration:
(1)
where Rtd is the calibrated luminous reflectance factor for that measurement configuration. When the illumination configuration Is a uniform hemispherical illumination, then R,jd is equivalent to luminou5 reflectance p%td• The luminous reflectance value associated with the standard is only valid for the hemispherical illumination in which It was calibrated. ii it is used with a directed source at any angle, there is no reason to expect that the luminous reflectance value will be the correct luminous reflectance factor value for that illumination configuration or spect’a.
The terms luminous reflectance and luminous reflectance factor shall be abbreviated to reflectance and reflectance factor, respectively.
Black glass (e.g., BG-1000J, or a very high neutral density absorption filter (density oF 4 or larger), can be used to determine the luminance of a source L from the measured luminance Ltd of the virtual
source image as reflected by the black glass, and the luminous specubr reflectance j of the black glass Ear the measurement configuration used:
When making specular measurements, the detector is locused on the virtual image ol the source. Black glass can be considered as a front surface mirror that has a low specular reflectance of between 4 % and 5 %. A black glass standard can be helpful when the measurement geometry does not allow measuring the source luminance directly, but only by using a mirror. The low specuLar reflectance of black glass allows measuring the source luminance at about the same order of magnitude as the reflection measurement.
The specular reflectance of black glass is affected by the specular angle, the illumination spectrum. and the cleanliness ot its surface. The calibration shall be repealed when the measurement geometry is changed.
6 PreparatIon of lentlcular print samples
6.1 Test pattern
The lenticular images are divided by several picture elements for one lenticular lens width, as shown In Figure 4. For the measurements of this document, striped test patterns shall be used, where each strip element shall be white or black, or other primary colours.
The precise alignment of the lentwular lens and the printed lenticubr image is essential. The procedures br the printing of high quality lenticular images are described in AnnexiL
7 Measurements and calculations
7.1 General
ISO TS 20793 specifically describes the measurement methods of the density and the evaluation methods for the following critical attributes of lenticular prints for changing Images:
a) cross-talk of lenticubr images:
b) viewing direction angle range of a lentlcubr Image:
c) divergence from the designed viewing direction angle of the main lenticular Image;
d) uniformity of the image within the printing area.
These attributes are critical for high quality lenticular prints For changtng images. These items are measured by changing the angle ul the print to the plane of the light measurement device (LMD).
7.2 Measurements of angular dependence
The measurements of the viewing direction dependence oldensity shall be done using the measurement system described In CiaussS.
For black and white images, all white patches, all black patches, and patches with a mlcro’strlped pattern that are illustrated In Flaure 4 and Tables 1 or 2 shall be measured. For colour Images, the black striped pattern shall be replaced with a primary colour, I.e. yellow, magenta, or cyan, or with a secondary colour, I.e. red, green, or blue.
The reflected light from the lenticular print shall be measured From the normal direction of the print.
Then, the print shall be rotated as shown In FIgure 1 or Figure 2. The reflected light shall be measured
In Intervals of 2° from —45° to +45°.
The visual density shall be calculated with Formula (3). in accordance with ISO 5-3 and ISO 5-4.
Dy8 =—log(1s8 /1w0 (3)
Iwo Is the intensity of the reflected light at an angle 9 from the standard white board calibrated as described in sub-cLause 5.i and Is Is the intensity of the reflected light at an angle 9 from the sample. Is and IW are calculated from spectrum data with ñwmula44j and Formu1aL5) respectively
8 ClassIfications
8.1 General
Cross-talk viewing direction angle range, angular misalignment, and uniformity in printing area shall be reported. The importance or each item depends on the use application. For example. for a business card, which shows different images and text, cross talk may he bothering but the viewing angle range may not be critical because It is viewed by properly adpusting the angle. For a poster, both cross4alk and the viewing angle range may be criticaL The guidelines or the dassification are described In this clause.
8.2 Cross-talk
Cross-talk value. CT(x), shall bc reported as described In Z. The level of the cross-talk shall be classified as shown in TahIci Cross-alk shall be reported as described in Z1.