In this paper, the current technologies in full colour 3D printing technology were introduced. A framework of colour image reproduction process for 3D colour printing is proposed. A special focus was put on colour management for 3D printed objects. Two approaches, colorimetric colour reproduction and spectral based colour reproduction are proposed in order to faithfully reproduce colours in 3D objects. Two key studies, colour reproduction for soft tissue prostheses and colour uniformity correction across different orientations are described subsequently. Results are clear shown that applying proposed colour image reproduction framework, performance of colour reproduction can be significantly enhanced. With post colour corrections, a further improvement in colour process are achieved for 3D printed objects.
Proc. SPIE. 9524, International Conference on Optical and Photonic Engineering (icOPEN 2015)
KEYWORDS: Light sources, Light emitting diodes, Visualization, Calibration, Image segmentation, Inspection, Optical inspection, Light sources and illumination, High dynamic range imaging, RGB color model
Glare is caused by both direct and indirect light sources and discomfort glare produces visual discomfort, annoyance, or loss in visual performance and visibility. Direct glare is caused by light sources in the field of view whereas reflected glare is caused by bright reflections from polished or glossy surfaces that are reflected toward an individual. To improve visual comfort of our living environment, a portable inspection system to estimate direct glare of various commercial LED modules with the range of color temperature from 3100 K to 5300 K was developed in this study. The system utilized HDR images to obtain the illumination distribution of LED modules and was first calibrated for brightness and chromaticity and corrected with flat field, dark-corner and curvature by the installed algorithm. The index of direct glare was then automatically estimated after image capturing, and the operator can recognize the performance of LED modules and the possible effects on human being once the index was out of expecting range. In the future, we expect that the quick-response smart inspection system can be applied in several new fields and market, such as home energy diagnostics, environmental lighting and UGR monitoring and popularize it in several new fields.
Color dithering methods for LEGO-like 3D printing are proposed in this study. The first method is work for opaque
color brick building. It is a modification of classic error diffusion. Many color primaries can be chosen. However,
RGBYKW is recommended as its image quality is good and the number of color primary is limited. For translucent
color bricks, multi-layer color building can enhance the image quality significantly. A LUT-based method is proposed
to speed the dithering proceeding and make the color distribution even smoother. Simulation results show the proposed
multi-layer dithering method can really improve the image quality of LEGO-like 3D printing.
Field sequential color (FSC) LCD without color filters has been proposed to enhance light efficiency and color gamut.
However, a well-known intrinsic visual artifact, color breakup, is perceived when a relative velocity exists between the
object on the screen and the observer's eyes. A Stencil-FSC method therefore was proposed recently which cumulates
major color information to the first color sub-frame and therefore suppresses the color breakup. However, the display
luminance is lower than that of conventional LCDs. To solve this problem, we extend the Stencil-FSC method to
display high dynamic range (HDR) images. Its first step is to scale HDR RGB signals to baseline RGB dynamic range.
Afterward, performs the original Stencil-FSC method to initialize all setting. Third, checks each backlight color zone of
the R, G, B sub-frames to see if they are free for changing their original primaries to RGB mixing primaries. Forth,
determines the color-mixing state of the 'free' primaries based on the extra HDR RGB signals. Finally, calculates the
LC signals of the new color-mixing primaries. This algorithm would upgrade a FSC LCD as HDR display.
Field sequential color (FSC) LCD is one of the preferred display technologies to achieve wide color gamut and high
luminous efficiency. But this technology suffers from an unpleasing color breakup effect. This phenomenon can be
reduced by adding a white primary. As RGBW primaries are recommended for FSC-LCD, the next question is how to
convert standard RGB signals to RGBW without large color variations.
The present study first optimal the spectra of RGB primaries using the 3D gamut boundaries of standard object color
spectra (SOCS) database and Adobe RGB in CIECAM02 space with observer metamerism constraint. The optimal
RGB primaries then were used to derive six modes for RGB to RGBW conversion. The final step is to further optimize
color correction matrix based on CIE170-1:2006 'age and size dependent cone fundamentals' to compensate the visual
color shift of elders.
The paper presents two models to reduce the visibility of rainbow effect for field sequential color (FSC) LCDs. It was
done by changing the LED backlight state, introducing crosstalk among the R/G/B LEDs and finally modified the RGB
signals to minimize its image color differences to its original state. The results of our simulations suggested that the
proposed methods would reduce the visibility of rainbow effect to some extent. However, its performance was quite
image-dependent. How to reduce its computational cost and calibrate the LED backlight accurately is a great challenge
to implement the models on real FSC LCDs.
The present study provides functions to correlate gamut size across different color spaces including 2D planes - (x,y)
and (u',v') and 3D spaces - CIELAB, CIECAM02 JCh and QMh. All gamut size must be converted to NTSC gamut
ratio before using the functions. As viewing conditions influence 3D gamut ratio significantly, predict 3D gamut ratio in
high precision is not easy. However, the mean values, median values, standard deviations, and confidence intervals can
be predicted accurately. In terms of viewing parameters, we can model them individually under IEC reference condition
successfully, the resulted functions would be a good reference to derive more versatile functions to predict gamut ratio
under complex viewing conditions.
The color fidelity of displays such as LCD and PDP was commonly estimated by a series of color patches. However, no strong evidence showed that these color patches are well correlated to the real-world image characteristics. To minimize the gap between the color patches and the image characteristics, the present study first accumulated the statistics of different classes of image. Then, we chose several of them as reference images, manipulated their colors intentionally, and finally asked observers to compare the reference images with their color-perturbed counterparts. In the end, based on the classified image statistics, an empirical model was derived to predict the overall results of the visual image differences. In the model, the pixel frequencies (probability) of 125 color clusters summarized by a certain type of images were taken into account for predicting the displays' color fidelity on the type of images. The 125 color clusters were linked in a 5x5x5 cellular structure. If the color manipulation breaks the intera-relationship of the cellular structure, the reproduction would be unnatural. In contrast, if the manipulation shifts the colors without breaking the relationship, the reproduction still looks fine. We called the intera-relationship as Cellular Uniformity and integrated the measurement into our model. It could be an interesting idea for future development on image quality assessment.
Color gamut mapping has been recognized as one of the key elements for accurate image reproduction. A variety of gamut mapping algorithms (GMAs) has been proposed to minimize the image differences between originals and their reproductions across different media. However, the use of a single-GMA is normally unable to fulfill all types of image reproductions. Therefore, we doubt if it’s a right way to further improve the performance of a single algorithm while increasing its complexity. In this study, we propose an optimal multi-GMAs approach based on image analysis to select an appropriate GMA from a range of LUT-type GMAs to give the image the best treatment at low-computational cost. Because there are too many image statistics can be extracted from an image, the present study introduces methods to select the principal statistics for the GMA selection. To save the cost for real-time image analysis, the importance of scanning patterns and image compression was investigated as well. The results suggested that the performance of the above applications would be enhanced to a certain level if we choose appropriate image statistics for calculation.
Previous work on color reproduction has shown that all existing solutions perform in ways that are image dependent. A series of experiments has therefore been carried out to systematically study the influence of a range of image characteristics on color reproduction and it was previously shown that neither image gamuts nor one-dimensional color histograms play an important role. The aim of the present paper then is to investigate whether the 3D histogram of image's colors is an image characteristic that significantly influences the performance of gamut mapping algorithms (GMAs). As this is done with the help of sets of artificial images, where each member of the set has different content but the same 3D color histogram, their use in studying color reproduction is also discussed in this paper. The results of a psychophysical experiment evaluating the influence of 3D color histograms on color reproduction are presented and analyzed in detail. These results show clearly that a significant proportion (approximately 2/3 to 3/4) of the variation in GMA performance caused by differences in image characteristics is due to 3D color histograms.
The color gamuts of color imaging media are important parameters in the reproduction of color images between them and their assumed magnitudes directly influence the degree to which colors are modified. In spite of this, the determination of gamut boundaries is often done in a way that ignores some basic implications that follow from the definition of color gamuts. This is partly due to the fact that some of these implications are not understood and partly due to the fact that if they are understood their magnitude is underestimated. Hence, the approach that is taken in this paper is to first discuss the theoretical implications of what color gamuts are and subsequently to illustrate them by experimental means..