PortaChrome: A Portable Contact Light Source for Integrated Re-Programmable Multi-Color Textures
PortaChrome：用于集成可重新编程的多色纹理的便携式接触光源
DOI: https://doi.org/10.1145/3654777.3676458
DOI： https://doi.org/10.1145/3654777.3676458
UIST '24: The 37th Annual ACM Symposium on User Interface Software and Technology, Pittsburgh, PA, USA, October 2024
UIST '24： 第 37 届 ACM 用户界面软件与技术年度研讨会 ，美国宾夕法尼亚州匹兹堡，2024 年 10 月
In this paper, we present PortaChrome, a portable light source that can be attached to everyday objects to reprogram the color and texture of surfaces that come in contact with them. When PortaChrome makes contact with objects previously coated with photochromic dye, the UV and RGB LEDs inside PortaChrome create multi-color textures on the objects. In contrast to prior work, which used projectors for the color-change, PortaChrome has a thin and flexible form factor, which allows the color-change process to be integrated into everyday user interaction. Because of the close distance between the light source and the photochromic object, PortaChrome creates color textures in less than 4 minutes on average, which is 8 times faster than prior work. We demonstrate PortaChrome with four application examples, including data visualizations on textiles and dynamic designs on wearables.
在本文中，我们介绍了 PortaChrome，这是一种便携式光源，可以连接到日常物品上，以重新编程与它们接触的表面的颜色和纹理。当 PortaChrome 与先前涂有光致变色染料的物体接触时，PortaChrome 内部的 UV 和 RGB LED 会在物体上创建多色纹理。与之前使用投影仪进行换色的工作相比，PortaChrome 具有轻薄而灵活的外形，允许将换色过程集成到日常用户交互中。由于光源和光致变色物体之间的距离很近，PortaChrome 平均不到 4 分钟即可创建彩色纹理，这比以前的工作快 8 倍。我们通过四个应用示例演示了 PortaChrome，包括纺织品的数据可视化和可穿戴设备的动态设计。
CCS 概念： • 以人为本的计算 → 人机交互 （HCI）;
ACM Reference Format: ACM 参考格式：
Yunyi Zhu, Cedric Honnet, Yixiao Kang, Junyi Zhu, Angelina J Zheng, Kyle Heinz, Grace Tang, Luca Musk, Michael Wessely, and Stefanie Mueller. 2024. PortaChrome: A Portable Contact Light Source for Integrated Re-Programmable Multi-Color Textures. In The 37th Annual ACM Symposium on User Interface Software and Technology (UIST '24), October 13--16, 2024, Pittsburgh, PA, USA. ACM, New York, NY, USA 13 Pages. https://doi.org/10.1145/3654777.3676458
Yunyi Zhu、Cedric Honnet、Yixiao Kang、Junyi Zhu、Angelina J Zheng、Kyle Heinz、Grace Tang、Luca Musk、Michael Wessely 和 Stefanie Mueller。2024. PortaChrome：一种便携式接触光源，用于集成可重新编程的多色纹理。第 37 届 ACM 用户界面软件与技术年度研讨会 （UIST '24），2024 年 10 月 13 日至 16 日，美国宾夕法尼亚州匹兹堡。ACM，美国纽约州纽约 13 页。https://doi.org/10.1145/3654777.3676458
图 1：（a） PortaChrome 是一种柔性接触光源，可以对之前涂有光致变色材料的物体的外观进行重新编程。PortaChrome 集成了 UV 和 RGB LED，可使光致变色材料的颜色通道饱和和去饱和。PortaChrome 便携且灵活，可以连接到（b）背包以重新编程衣服的背面，（c）袖子内部以重新编程夹板支架，（d）无线充电器以重新编程设备的背面，以及（e）耳机外壳的内部以重新编程耳机的设计。
INTRODUCTION
引言
An important step towards achieving the vision of "The Ultimate Display" [33] is to augment the surfaces of objects with display capabilities, such as changing their color and visual texture, through novel display fabrication methods (DisplayFab [10]). This capability has initiated new application opportunities, allowing users to fit multiple designs on personal items such as phone cases and shoes [17] and to display relevant information in the daily environment, such as showing a calendar on a mug [34].
实现“终极显示”[33]愿景的重要一步是通过新颖的显示制造方法（DisplayFab [10]）增强物体表面的显示功能，例如改变其颜色和视觉纹理。这种能力开启了新的应用机会，允许用户在手机壳和鞋子等个人物品上适应多种设计[17]，并在日常环境中显示相关信息，如在杯子上显示日历[34]。
Researchers have developed systems with color-changing materials to augment object surfaces with display capabilities. For example, electrochromic [16] and thermochromic [8, 18] systems enable the transition between predefined color phases. Recently, researchers expanded the color gamut and allowed reprogrammable textures using photochromic dyes (Photo-Chromeleon [17]). By spraying a mixture of cyan, magenta, and yellow photochromic dyes on an object and projecting light patterns of specific wavelengths to saturate and desaturate individual color channels, the resulting photochromic object achieves high-resolution multi-color textures that are fully reprogrammable.
研究人员开发了具有变色材料的系统，以增强具有显示功能的物体表面。例如，电致变色 [16] 和热致变色 [8， 18] 系统支持预定义色相之间的过渡。最近，研究人员扩大了色域并允许使用光致变色染料 （Photo-Chromeleon [17]） 重新编程纹理。通过在物体上喷涂青色、品红色和黄色光致变色染料的混合物，并投射特定波长的光图案以使各个颜色通道饱和和去饱和，所得的光致变色物体实现了完全可重新编程的高分辨率多色纹理。
One limitation of a projector system for reprogrammable surfaces is that it has to be set up at a distance from the object to induce color change, limiting the types of interactions that can leverage texture reprogramming. More portable light sources enable new ways to interact with photochromic material. For example, researchers of photochromic systems have considered portable light sources to integrate color-change into users’ everyday interaction, such as integrating a UV LED matrix into shoes to allow reprogramming the carpet while walking (PhotochromicCarpet [28]).
用于可重新编程表面的投影仪系统的一个限制是，它必须设置在与对象保持一定距离的地方以引起颜色变化，从而限制了可以利用纹理重新编程的交互类型。更便携的光源为与光致变色材料交互提供了新的方式。例如，光致变色系统的研究人员已经考虑将便携式光源将颜色变化集成到用户的日常互动中，例如将 UV LED 矩阵集成到鞋子中，以允许在行走时对地毯进行重新编程 （PhotochromicCarpet [28]）。
However, the portable light sources used in photochromic systems so far have only supported single-color textures. To enable multi-color textures, light sources do not only require UV wavelength for saturation but also RGB wavelengths for individually desaturating each color channel. In addition, the portable light source used in existing photochromic systems has been rigid (e.g., rigid UV LED matrices) and thus limited the color change to flat surfaces. To enable multi-color textures on curved surfaces, such as on the curved headpiece of a pair of headphones, a flexible light source that can conform to the curved surface and has both RGB and UV wavelengths is needed. Existing flexible displays, such as commercial O-LED displays, contain RGB wavelengths, which are necessary to desaturate the photochromic dyes, but are missing the UV wavelength required for saturation.
然而，到目前为止，光致变色系统中使用的便携式光源仅支持单色纹理。要启用多色纹理，光源不仅需要 UV 波长来实现饱和，还需要 RGB 波长来单独降低每个颜色通道的饱和度。此外，现有光致变色系统中使用的便携式光源是刚性的（例如，刚性 UV LED 矩阵），因此将颜色变化限制在平面上。要在曲面上启用多色纹理，例如在一副耳机的曲面头件上，需要一个能够符合曲面并同时具有 RGB 和 UV 波长的柔性光源。现有的柔性显示器（如商用 O-LED 显示器）包含 RGB 波长，这些波长是降低光致变色染料饱和度所必需的，但缺少饱和所需的 UV 波长。
In this paper, we present PortaChrome: a flexible and portable light source that supports re-programmable multi-color texture on photochromic objects (Figure 1). With a thickness of 6mm, PortaChrome can be embedded into surfaces that come in contact with photochromic objects, integrating the texture reprogramming process into the user's everyday interactions. This enables applications such as visualizing the user's heart rate on the back of a T-shirt the user is wearing while hiking with a PortaChrome-augmented backpack (Figure 1 b), matching the color of a splint brace with the user's everyday outfit with a PortaChrome embedded inside the user's sleeves (Figure 1 c), displaying exercise progress with PortaChrome attached to a wireless charger (Figure 1 d), and switching the design of a headphone with PortaChrome integrated into the headphone casing (Figure 1 e). We accomplish this by making flexible panels of RGB and UV LEDs on a textile substrate and using a silicone structure to distribute the light evenly on the surface of the object in contact. Our system also reprograms the color of an object in under 4 minutes on average, which is 8 times faster than prior work.
在本文中，我们介绍了 PortaChrome：一种灵活的便携式光源，支持光致变色物体上的可重新编程多色纹理（图 1）。PortaChrome 的厚度为 6 毫米，可以嵌入到与光致变色物体接触的表面，将纹理重编程过程集成到用户的日常交互中。这使得诸如在用户使用 PortaChrome 增强背包远足时穿着的 T 恤背面可视化用户的心率（图 1 b）等应用，将夹板支架的颜色与用户的日常服装相匹配，将 PortaChrome 嵌入在用户袖子内（图 1 c），显示连接到 PortaChrome 的锻炼进度（图 1d） 以及切换耳机外壳中集成了 PortaChrome 的耳机设计（图 1 e）。我们通过在纺织基材上制作 RGB 和 UV LED 柔性面板，并使用硅胶结构将光线均匀分布在接触物体的表面上来实现这一目标。我们的系统还可以在平均 4 分钟内重新编程对象的颜色，这比以前的工作快 8 倍。
In summary, we contribute:
总而言之，我们贡献了：
- a fabrication method to create a flexible and portable contact light source made from UV and RGB LEDs on a textile substrate that can be attached to everyday objects to reprogram photochromic objects that are in contact;
一种制造方法，用于在纺织基材上由 UV 和 RGB LED 制成柔性和便携式接触光源，该光源可以连接到日常物体上，以重新编程接触的光致变色物体; - a developer tool for specifying the desired color pattern and an algorithm that computes the time of light exposure of each wavelength on each pixel to achieve the desired pattern;
用于指定所需颜色图案的开发人员工具和计算每个像素上每个波长的曝光时间以实现所需图案的算法; - a technical evaluation showing that our approach based on a flexible contact light source leads to an 8 times speed increase (4 minutes on average vs. 32 minutes) in texture transfer time;
技术评估表明，我们基于柔性接触光源的方法使纹理传输时间提高了 8 倍（平均 4 分钟对 32 分钟）; - four applications that showcase PortaChrome's capability to reprogram object appearance through everyday interaction, including data visualizations on textiles and personalized designs on wearables.
这四个应用程序展示了 PortaChrome 通过日常交互重新编程对象外观的能力，包括纺织品上的数据可视化和可穿戴设备上的个性化设计。
RELATED WORK
相关工作
We review the relevant work in color-changing systems, light sources for photochromic materials, and flexible emissive displays.
我们回顾了变色系统、光致变色材料的光源和柔性自发光显示器方面的相关工作。
Application of Color-changing Materials
变色材料的应用
Researchers in HCI have used color-changing materials to achieve a dynamic visual appearance for different applications. For instance, researchers have created programmable designs on textiles coated with thermochromic material (Shimmering Flowers [2], Embr [8]), which can be extended to animations on personal garments, such as demonstrated in Animated Quilt [3] and Project Primrose [7]. Programmable color change has also been leveraged for on-skin interfaces, for instance, by using thermochromic pigments for make-up (ChromoSkin [18]) and tattoos (DuoSkin [19]). In addition, as outlined in DisplayFab [10], researchers have also used color-changing materials to create single-color bespoke displays that can be easily integrated into daily environment with electroluminescent coating (PrintScreen [23], ProtoSpray [12], Sprayable UI [36]), electrochromic ink (Decocrom [16]), e-ink microcapsules (FabricatINK [11]) and 3D printed magnetophoretic structures [39]. Finally, researchers have used photochromic material to create reprogrammable multi-color appearances on everyday objects, such as shoes and phone cases (PhotoChromeleon [17]) and to turn daily objects into IoT devices that can display various types of data, such as user calendar and daily weather on a coffee mug (ChromoUpdate [35]). Our work contributes to multi-color reprogrammable appearance and specifically focuses on a new reprogramming light source for photochromic color-changing materials that is both flexible and portable.
HCI 的研究人员使用变色材料为不同的应用实现动态视觉外观。例如，研究人员在涂有热致变色材料的纺织品上创建了可编程设计（Shimmering Flowers [2]、Embr [8]），这些设计可以扩展到个人服装上的动画，例如动画被子 [3] 和樱草花项目 [7] 中演示的动画。可编程的颜色变化也被用于皮肤界面，例如，使用热致变色颜料进行化妆 （ChromoSkin [18]）和纹身 （DuoSkin [19]）。此外，正如 DisplayFab [10] 中所述，研究人员还使用变色材料制造了单色定制显示器，这些显示器可以通过电致发光涂层（PrintScreen [23]、ProtoSpray [12]、 可喷涂用户界面 [36]）、电致变色油墨（Decocrom [16]）、电子墨水微胶囊（FabricatINK [11]）和 3D 打印磁团结构 [39]。最后，研究人员使用光致变色材料在日常物品（如鞋子和手机壳）上创建可重新编程的多色外观 （PhotoChromeleon [17]），并将日常物品转化为可以显示各种类型数据的物联网设备，例如用户日历和咖啡杯上的每日天气 （ChromoUpdate [35]）。 我们的工作有助于实现多色可重新编程的外观，并特别关注一种用于光致变色材料的新型重新编程光源，该光源既灵活又便携。
Portability of Light Sources for Photochromic Objects
光致变色物体光源的便携性
Researchers have developed light sources for photochromic materials with different levels of portability and integration. Light sources that operate from a distance, such as projectors and lasers, require the user to place the object inside an enclosure for the color-changing process to ensure the user's safety from the high-intensity UV light. For instance, Slow Display [27] and UbiChromics [1] use UV vector laser projectors to create high-resolution single-color textures on 3D objects and walls with a mounted projection set up. Photochromic Sculpture [14] reprograms a volumetric display made from a stack of acrylic sheets coated with photochromic material with a UV projector. ColorMod [25], Photo-Chromeleon [17] and ChromoUpdate [34] use RGB and UV projectors set up in an enclosure to reprogram the appearance of objects either 3D printed in the form of photochromic voxels or coated with CMY photochromic material post hoc.
研究人员已经开发出具有不同便携性和集成度的光致变色材料的光源。远距离工作的光源（例如投影仪和激光器）要求用户将物体放置在外壳内以进行变色过程，以确保用户免受高强度紫外线的影响。例如，Slow Display [27] 和 UbiChromics [1] 使用紫外矢量激光投影仪在 3D 对象和墙壁上创建高分辨率的单色纹理，并安装了投影。 光致变色雕塑 [14] 用紫外线投影仪对由一堆涂有光致变色材料的亚克力板制成的体积显示器进行重新编程。ColorMod [25]、Photo-Chromeleon [17] 和 ChromoUpdate [34] 使用安装在外壳中的 RGB 和 UV 投影仪对物体的外观进行重新编程，这些物体要么以光致变色体素的形式 3D 打印，要么事后涂有 CMY 光致变色材料。
More portable light sources enable new ways to interact with photochromic material. For example, Photochromic Canvas [13] uses a pen-shaped hand-held projector that when held closely to a piece of paper with saturated single-color photochromic dyes results in desaturation while the user draws. KAMI-CHAT [24] uses a UV LED matrix that is in direct contact with photochromic paper to create single-color patterns. Photochromic Carpet [28] places UV LEDs under the users’ shoes that come in contact with a photochromic carpet as the user walks over it, thereby creating single-color patterns. However, so far the portable light sources used in photochromic systems have been rigid and only employed one wavelength (i.e., UV) to saturate a single-color photochromic surface. With PortaChrome, we create a flexible and portable light source that provides RGB and UV wavelengths to create multi-color textures by making direct contact with the object.
更便携的光源为与光致变色材料交互提供了新的方式。例如，Photochromic Canvas [13] 使用笔形手持式投影仪，当它紧贴一张带有饱和单色光致变色染料的纸时，会导致用户绘图时饱和度降低。KAMI-CHAT [24] 使用与光致变色纸直接接触的 UV LED 矩阵来创建单色图案。 光致变色地毯 [28] 将紫外线 LED 放置在用户的鞋子下方，当用户走过光致变色地毯时，这些 LED 会与光致变色地毯接触，从而产生单色图案。然而，到目前为止，光致变色系统中使用的便携式光源一直是刚性的，并且只使用一种波长（即 UV）来使单色光致变色表面饱和。通过 PortaChrome，我们创建了一个灵活且便携的光源，提供 RGB 和 UV 波长，通过与物体直接接触来创建多色纹理。
Flexible Emissive Displays
灵活的自发光显示器
Researchers developed different methods to create flexible displays, which have the potential to be used as a light source for photochromic material. Non-emissive displays, such as e-ink [9, 11], do not emit light and are thus not suitable to program photochromic materials. We therefore focus our review on flexible emissive displays, which have integrated light sources that can emit wavelengths in the spectrum required to program photochromic materials.
研究人员开发了不同的方法来制造柔性显示器，这些显示器有可能用作光致变色材料的光源。非自发光显示器，如电子墨水 [9， 11]，不发光，因此不适合对光致变色材料进行编程。因此，我们将重点放在柔性自发光显示器上，它集成了光源，可以发射编程光致变色材料所需光谱中的波长。
One type of flexible emissive display with integrated light sources that emit RGB wavelengths are OLED screens [6]. However, current commercial OLED screens lack the UV light source required to saturate photochromic dyes. In addition, they are not flexible enough to conform to objects with varying object geometries. A type of flexible display that can be made in makerspaces are thin-film electroluminescent displays (PrintScreen [23], FoldIO [22]). Such displays have also been embedded into materials that can conform to various surface geometries either by embedding the display in stretchable silicone (Stretchis [37]) or by integrating it into a textile (Shi et al. [31]). However, electroluminescent displays cannot provide the RGB and UV wavelengths required to program photochromic dyes.
OLED 屏幕是一种带有集成光源的柔性自发光显示器，可发射 RGB 波长 [6]。然而，目前的商用 OLED 屏幕缺乏使光致变色染料饱和所需的紫外线光源。此外，它们不够灵活，无法适应具有不同对象几何图形的对象。薄膜电致发光显示器（PrintScreen [23]、FoldIO [22]）是一种可以在创客空间中制造的柔性显示器。通过将显示器嵌入可拉伸硅胶 （Stretchis [37]）或将其集成到纺织品中 （Shi et al.[31]）。但是，电致发光显示器无法提供对光致变色染料进行编程所需的 RGB 和 UV 波长。
Another approach is to use light fibers to redirect emitted light from a rigid light source to flexible and curved surfaces. For example, LightCloth [15] and Optical Fiber Fabric Display [20] use optical fibers to route light from a 1D LED array to a flexible 2D surface. Printed Optics [38] and Papillon [4] use 3D printed light fibers to redirect the output of pixels from a rigid display to a predefined curved surface. However, due to non-controlled light attenuation in the fiber, these methods have non-uniform light distribution on the contact surface and cannot be used to accurately control the photochromic dye, which is required to achieve a desired target color.
另一种方法是使用光纤将发射的光从刚性光源重定向到柔性和曲面。例如，LightCloth [15] 和 Optical Fiber Fabric Display [20] 使用光纤将光从 1D LED 阵列路由到柔性 2D 表面。Printed Optics [38] 和 Papillon [4] 使用 3D 打印的光纤将像素输出从刚性显示器重定向到预定义的曲面。然而，由于纤维中的光衰减不受控制，这些方法在接触面上的光分布不均匀，无法用于精确控制光致变色染料，而光致变色染料是实现所需目标颜色所必需的。
More closely related to our work, researchers also investigated how to create flexible structures with integrated LEDs. Rein et al. [26], for instance, create fibers containing LEDs. However, their fibers only contain non-addressable LEDs with one wavelength per LED and do not provide UV LEDs. In addition, their fabrication approach requires highly specialized equipment, i.e., a fiber draw tower to manufacture the fibers. Using a more accessible approach, Choi et al. [5] weave commercially available addressable LED strips to create a room-scale textile-like display. However, commercially available LED strips currently do not contain UV LEDs, which are required for saturating the photochromic material. In PortaChrome, we create a flexible textile-based LED matrix that contains both UV and addressable RGB LEDs, satisfying the wavelength requirement for photochromic dyes while providing textile-like flexibility.
与我们的工作更密切相关的是，研究人员还研究了如何使用集成 LED 创建柔性结构。Rein 等人。[26]，例如，创建包含 LED 的光纤。但是，它们的光纤仅包含不可寻址的 LED，每个 LED 只有一个波长，不提供 UV LED。此外，他们的制造方法需要高度专业化的设备，即纤维拉丝塔来制造纤维。Choi 等人 [5] 使用一种更容易获得的方法，编织了市售的可寻址 LED 灯条，以创建房间规模的类似纺织品的显示器。然而，市售的 LED 灯条目前不包含 UV LED，而 UV LED 是使光致变色材料饱和所必需的。在 PortaChrome 中，我们创建了一个基于纺织品的柔性 LED 矩阵，其中包含 UV 和可寻址 RGB LED，满足光致变色染料的波长要求，同时提供类似纺织品的灵活性。
PORTACHROME
图 2：PortaChrome 将纹理重新编程过程集成到日常用户交互中：（a） 用光致变色材料处理的物体;（b） PortaChrome 可以安装在与光致变色物体接触的另一个物体的表面上;（c） PortaChrome 在与光致变色物体接触时对其进行重新编程;（d） 光致变色物体可以重新编程以显示不同的图案。
图 3：PortaChrome 的结构：（a） PortaChrome 由四层组成：织物基层、RGB LED 织物层、UV LED 织物层和有机硅扩散层。（b） 集成的 UV 和 RGB LED 使 PortaChrome 能够使光致变色涂层饱和和去饱和，从而将表面像素编程为所需的目标颜色。
Integrated Color-Changing Process
集成换色工艺
PortaChrome can be embedded in everyday objects, thereby integrating the texture reprogramming process into everyday user interactions. PortaChrome is designed to be embedded into an object and then reprogram the color of another object previously coated with photochromic dye through direct contact. Figure 2 shows this in more detail, i.e. in Figure 2 a an object is treated with photochromic dye, allowing its color to be later reprogrammed with PortaChrome. This object can be the back of a T-shirt, a splint brace, the back of a tablet, and a headphone, as illustrated in the application scenarios. PortaChrome can then be attached to another object that will be in contact with the photochromic object (Figure 2 b), such as a backpack, the inside of a sleeve, a wireless charger, and the inside of the casing. When in contact, PortaChrome illuminates UV and RGB light that reprogram the texture of the photochromic object (Figure 2 c), allowing the object to display a different texture after programming is completed (Figure 2 d).
PortaChrome 可以嵌入到日常物品中，从而将纹理重新编程过程集成到日常用户交互中。PortaChrome 被设计为嵌入到一个物体中，然后通过直接接触重新编程之前涂有光致变色染料的另一个物体的颜色。图 2 更详细地显示了这一点，即在图 2 中，一个物体被光致变色染料处理，允许其颜色稍后使用 PortaChrome 重新编程。此对象可以是 T 恤的背面、夹板支架、平板电脑的背面和耳机，如应用程序方案所示。然后，可以将 PortaChrome 连接到将与光致变色物体接触的另一个物体上（图 2 b），例如背包、袖套内部、无线充电器和外壳内部。接触时，PortaChrome 会照亮 UV 和 RGB 光，这些光会重新编程光致变色物体的纹理（图 2 c），从而允许物体在编程完成后显示不同的纹理（图 2 d）。
Unlike previous works that use projectors for multi-color photochromic texture, PortaChrome enables an integrated color-changing process that does not require the user to actively design and initiate the reprogramming. This enables new interactions to create reprogrammable textures, such as data visualization that automatically update based on sensor data.
与以前使用投影仪进行多色光致变色纹理的作品不同，PortaChrome 实现了一个集成的变色过程，不需要用户主动设计和启动重新编程。这使得新的交互能够创建可重新编程的纹理，例如根据传感器数据自动更新的数据可视化。
PortaChrome Composition
PortaChrome 组合
PortaChrome consists of four layers (Figure 3 a): (1) a fluorescent textile base layer that filters out the UV light from the UV LEDs to protect the user, (2) a flexible UV LED circuit on a transparent textile for saturating the color of the photochromic dye; (3) a flexible addressable RGB LED circuit on a transparent textile for desaturating the color of the photochromic dye; and (4) a silicone diffusion layer to more evenly distribute the light from the UV and RGB LEDs to their corresponding pixels on PortaChrome's surface.
PortaChrome 由四层组成（图 3 a）：（1） 荧光织物基层，用于过滤来自 UV LED 的紫外线以保护用户，（2） 透明织物上的柔性 UV LED 电路，用于饱和光致变色染料的颜色;（3） 透明织物上的柔性可寻址 RGB LED 电路，用于降低光致变色染料的颜色饱和度;（4） 有机硅扩散层，以更均匀地将来自 UV 和 RGB LED 的光分布到 PortaChrome 表面上的相应像素。
Flexible UV and RGB LED Circuits: PortaChrome incorporates both UV LEDs and addressable RGB LEDs to be able to create multi-color reprogrammable textures. The UV LEDs (WL-SUTW, 0.216W) are responsible for saturating the photochromic dye, turning its color from clear to black. The RGB LEDs (SK6812, 0.3W) then selectively desaturate the cyan, magenta, and yellow (C,M,Y) channels of the dye, changing its color from black to a specific target color. To achieve pixel-level control, each addressable RGB LED corresponds to a single pixel of the saturated color (Figure 3 b).
灵活的 UV 和 RGB LED 电路：PortaChrome 结合了 UV LED 和可寻址 RGB LED，能够创建多色可重新编程的纹理。UV LED （WL-SUTW， 0.216W） 负责使光致变色染料饱和，将其颜色从透明变为黑色。然后，RGB LED（SK6812,0.3W）选择性地降低染料的青色、品红色和黄色 （C，M，Y） 通道的饱和度，将其颜色从黑色更改为特定的目标颜色。为了实现像素级控制，每个可寻址 RGB LED 对应于饱和颜色的单个像素（图 3 b）。
Silicone Diffusing Layer: Because the UV and RGB LEDs are point light sources, they do not provide uniform light intensity across an area. To address this, PortaChrome includes a silicone diffusion layer that distributes light more evenly across each pixel.
硅胶扩散层： 由于 UV 和 RGB LED 是点光源，因此它们无法在整个区域内提供均匀的光强度。为了解决这个问题，PortaChrome 包括一个硅胶扩散层，它可以将光线更均匀地分布在每个像素上。
UV Protection Layer: PortaChrome only requires low-power UV LEDs to saturate the photochromic dyes because of the close distance to the material. During the reprogramming process, the UV LEDs are oriented towards the object, and thus only reflected light can reach the user. This reflected light is at a wavelength of 365 nm and falls within the UVA spectrum, which falls under ‘blacklight (320-400 nm) [that] does not represent a hazard under normal use conditions’1. To further filter out these low intensity UV light reflections, PortaChrome includes a textile base layer made of fluorescent fabric that absorbs UV light.
紫外线防护层：PortaChrome 只需要低功率 UV LED 来使光致变色染料饱和，因为与材料的距离很近。在重新编程过程中，UV LED 朝向物体，因此只有反射光才能到达用户。这种反射光的波长为 365 nm，属于 UVA 光谱，属于“黑光 （320-400 nm） [在正常使用条件下] 不构成危险”1。为了进一步过滤掉这些低强度的紫外线反射，PortaChrome 包括一个由荧光织物制成的织物基层，可吸收紫外线。
Device Hardware & Fabrication
We first analyze the design criteria of the PortaChrome light source and then develop a fabrication method to create the light source on a flexible substrate.
LED Spectrum, Arrangement and Circuit Design
To design the PortaChrome light source, we first chose RGB and UV LEDs compatible with the photochromic dye's saturation and desaturation wavelengths. Next, we considered the optimal arrangement of the LEDs to create an even light distribution on PortaChrome's surface. Finally, we designed the LED circuit to avoid voltage drops that would lead to uneven light output.
LED Spectrum: To saturate the photochromic dyes, we chose UV LEDs (WL-SUTW) with a wavelength of 365nm, which is the same wavelength as used in prior work (PhotoChromeleon [17]) and a size large enough for hand-soldering (3.5mm x 2.8mm). To choose an addressable RGB LED that has the wavelengths appropriate for desaturating the CMY color channels of the photochromic dye, we compared different addressable RGB LEDs on the market. We found that they all have similar wavelengths and only differ in housing sizes. We thus chose to use a Neopixel 5050 addressable RGB LED (SK6812), which is large enough for hand-soldering (size: 5mm x 5mm). Figure 5 shows the Neopixel's LEDs wavelength spectrum for each color channel together with the absorption spectrum of the CMY color channels of the photochromic dye. It can be seen from the diagram that each LED wavelength is capable of desaturing one color channel with only small overlap on the other two, which allows us to achieve a desired target color by selectively activating the R, G, B LEDs.
Device Fabrication
To fabricate PortaChrome, we laser-cut copper mesh to create flexible conductive traces, solder the LEDs onto the traces, and then adhere the assembled traces to a chiffon fabric using textile glue. Finally, we add a silicone-casted diffusion layer and a UV absorbing fabric to filter out the light from the UV LEDs to protect the user.
Laser Cutting the Circuit and Soldering the LEDs: To construct the LED circuit, we use fiber laser cutting similar to the method used in Fibercuit [40] (model: MFP-B60, laser wavelength: 1064nm, power: 60W). The LED circuit panels are 6cm by 5.5cm in size and each contains 36 LEDs. This is limited by the size of the fiber laser cutter and the speed of manual soldering. The PortaChrome used in the application section is made by connecting 6 panels together to form a larger PortaChrome light source.
We identified four criteria for the material for the circuit: (1) flexibility to conform to different surfaces; (2) low electrical resistance to avoid voltage drop when powering the LED matrix; (3) compatibility with fiber laser cutting; and (4) solderability for electronic assembly. To fulfill these requirements, we use copper mesh (mesh count: 200) as the material for our conductive traces (Figure 4 a). Copper mesh is composed of interwoven strands of copper threads, allowing it to conform to a variety of curved surfaces, while having low-electrical resistance (0.05-Ohm along a strip of 3mm width and 15cm length), being laser-cuttable and solder-friendly. The mesh count refers to how many holes are in 1 inch of copper mesh and thus how flexible the copper mesh is with mesh counts ranging from 40 (least flexible) to 200 (most flexible) for commercially available copper mesh.
We start by adhering the copper mesh onto a single-side Kapton tape. We then attach the assembly to a ceramic base plate with the copper mesh side facing up before inserting it into the fiber laser cutter to create the traces (Figure 4 a/b). We remove any extra material and solder the LEDs directly onto the traces using a heat plate and solder paste (Figure 4 c/d). Next, we attach the finished circuit to a transparent chiffon textile substrate using textile glue. For this step, we use a laser-cut paper stencil to limit the glue to only the trace areas and vinyl transfer tape to precisely maintain the shape of the circuit (Figure 4 e-g). After creating the flexible textile circuit (Figure 4 h-j) for the RGB and UV LED layers, we use a sewing machine to stitch them together with a straight stitch along the two sides of the panels.
Silicone Molding the Diffusion Layer: To create the diffusion layer that distributes the light from the LED point light sources more evenly across each PortaChrome pixel, we designed the diffusion structure shown in Figure 8 a. Each pixel in the structure is 6mm thick, and corresponds to a hexagon pixel of 10mm diameter. Since the UV LEDs are located at the corners of each pixel on PortaChrome's device, we designed the diffusion structure to have sharp edges that allow the incident light to achieve total internal reflection, and thus direct the UV light to 3 adjacent pixels instead of at the corner (Figure 8 b). We also designed hexagonal holes in the center of each pixel, preventing the light from the RGB LEDs from creating hot spots by refracting them away from the center of each pixel.
To maintain the flexibility of the structure, we fabricate the diffuser with silicone (Smooth-on Sorta Clear 12) using SLA-printed molds (Figure 8 c). To prevent inhibition during the silicone curing process, we submerge the SLA-printed molds in isopropanol for 5 minutes, wash it with hand soap for 5 minutes using a brush, cure it under UV light at 40° C for 1 hour and coat each model with Inhibit-X spray, which prevents curing inhibition due to the uncured resin. After making the diffusion structure, we stick them onto the LED circuits with Sil-Poxy silicone glue.
In Figure 9, we compare our diffuser with other diffusion mechanisms of the same 6mm thickness and show its effect on how evenly the color changes on the affected pixel. From left to right: no diffusion (thickness: 0mm) results in center dots as is the expected result when using point light sources for saturation; a transparent spacer casted from silicone (thickness: 6mm) results in uneven color distribution because the UV and RGB LEDs are located in different positions; a generic uniform diffuser created by mixing silicone with 2w% glass balloons (diameter: 50μm), mitigates this issue, but the misalignment between UV saturation and RGB de-saturation still results in the pixel being darker in the center than on its edges. In contrast, our diffuser aligns the light from both types of LEDs yielding pixels with clearer edges and more even saturation within the internal area of each pixel.
Cutting the UV Protection Layer: We include a UV-filtering textile (Model: Rosco #3030, Grid Cloth) as the UV protection layer. To integrate it with the rest of the PortaChrome device, we cut the textile to match the contour of the device and use a sewing machine to stitch it along the edges, securing it beneath the LED layers and the UV protection layer.
USER INTERFACE
We built a control system for PortaChrome, with a control circuit based on the ESP32 microcontroller and a control script developed in Python. The system allows interaction designers to control the PortaChrome light source to reprogram the photochromic object by sending an input color array via Bluetooth. To assist the designer in creating the color array, we also built a design tool (developed in Processing Java) that allows the user to design a desired multi-color texture and simulate the outcome (Appendix). The system is open-source2. We will demonstrate how to use the system to complete a texture reprogramming process at the example of changing the color texture on the back of a T-shirt.
Control Circuit: We built a control circuit around an ESP32 microcontroller to connect the user interface with the PortaChrome hardware. Figure 10 a shows the schematic of this circuit and Figure 10 b shows a protoboard implementation of the control circuit connected to a PortaChrome device powered by a commercial portable power bank. The ESP32 listens for Bluetooth signals and initiates texture reprogramming when data is received via Bluetooth from other devices, such as the user's mobile phone.
EVALUATION
We evaluate PortaChrome's texture transfer time, the achievable color gamut and how well PortaChrome can wrap around surfaces of different angles.
Texture Transfer Speed
Apparatus: To evaluate the color reprogramming time, we measured the time for saturation and desaturation on white ceramic blocks sprayed with photochromic dye of a single color channel. Similar to ChromoUpdate [35], we spray coated the samples using an airbrush and mixed the spray paint by adding 0.033w% cyan, 0.033w% magenta, and 0.1w% yellow to Dupli-Color EBSP30000 Glossy Clear Coat spray paint, respectively.
Procedure: To measure the saturation time for each photochromic dye, we saturate each of the C,M,Y blocks under a 6x6 panel of UV LEDs for 0 to 40 seconds with 5 second intervals. After each 5 second saturation interval, we captured a picture of the sample using a Canon Rebel T6i camera. We color-corrected the pictures with a color checker, and sampled the averaged color of each panel pixel by averaging the hexagon area with a radius of 15 pixels around the area center. We then plotted the normalized average saturation value of all 6x6 panel pixels for each dye.
To measure the desaturation of each photochromic dye, we first saturate each block with UV LEDs for 15 seconds (which the previous evaluation showed is sufficient to fully saturate each dye) and then turn on the R, G or B lights for 0 to 200 seconds or until the color is fully desaturated. We follow the same procedure as in the saturation experiment by capturing the normalized saturation value of the color-corrected desaturated samples. We repeat this process three times and take the average of the resulting values.
The desaturation plots include red, green, and blue LEDs and feature two sets of lines for each color dye under each LED. The lighter lines depict the raw saturation levels, calculated based on the brightness of every individual pixel within each hexagon. Because of the uneven lighting within the photo, this raw data has periodic noise affected by the location of the pixel. To determine the actual time required for desaturation, we smoothed the values normalized with a fully-saturated sample as 1 and a fully-desaturated sample as 0, which are represented by the darker-colored lines in the plot. We compare our desaturation time for each color channel with previous work [35]. In our system, cyan takes 100 seconds to desaturate (previous work: 800s, time reduction: 87%), magenta takes 62 seconds to desaturate (previous work: 620s, time reduction: 90%), yellow takes 5 seconds to desaturate (previous work: 32s, time reduction: 84%). As a result, the total reprogramming time from our application scenarios, our system yields on average 87% faster reprogramming step (4 minutes vs 32 minutes) for the same photochromic dye mixture.
Flexibility
Apparatus and Procedure: To evaluate how the PortaChrome light source performs on curved surfaces, we 3D printed PLA blocks with both convex and concave radii of 0cm, 0.5cm, 1cm, 1.5cm, and 2cm and coated them with photochromic dye. We then fixed the PortaChrome light source around each block by clamping it with another block with an inverse geometry, illuminating the blocks with a pattern that had a single white pixel on the curved location. We compared the resulting texture effects to those achieved on a flat plane.
APPLICATIONS
We next showcase applications of PortaChrome with the example of a data visualization on a textile surface and a personal device, and a wrist splint and a headphone with reprogrammable customized visual appearance.
Visualize Sensor Data on Textiles with Backpack-Wearing
In our first application, we show how PortaChrome can be used to create a data visualization on a textile surface (Figure 14). In this example, we mounted PortaChrome on the inside of a backpack. When the user wears the backpack over a T-shirt previously coated with photochromic dye, the backpack updates the color pattern on the T-shirt while the user wears it.
In this specific example, we create a data visualization of the user's hiking experience. An altitude sensor and a heart rate sensor send data to the PortaChrome control system, which plots the altitude and heart rate as a data visualization on the T-shirt. Such a portable, contact-based application was not achievable with previous systems, which required projector setups. It is also enabled by PortaChrome's fast color change, which only took 3 minutes and 52 seconds for the hiking visualization.
Visualize Sensor Data on Back of Device during Wireless Charging
When electronic devices are wirelessly charged, their back surfaces are in contact with the wireless charging station. In this application, we demonstrate that the PortaChrome light source can be embedded into a wireless charging station, which allows it to reprogram the back of the device that is being charged. Figure 15 shows this with an example of a tablet that has its back coated with photochromic dye. In this example, we display the user's progress toward their weekly workout challenge, where two halves of a heart move closer together and eventually align as the user reaches their weekly workout goal. In this application, each reprogramming step takes only 2 minutes and 21 seconds to complete.
Reprogram a Wrist Splint through Jacket-Wearing
PortaChrome can also be used to visually customize rehabilitation devices, such as wrist splints, which has been shown to increase the adoption of such devices [32]. We demonstrate this concept with the example of a wrist splint, the color of which can be reprogrammed to match the wearer's daily outfit (Figure 16). By integrating PortaChrome into the sleeves of a jacket, the user can reprogram the texture while wearing the jacket over it. The three colors demonstrated in Figure 16 take 3 minutes 50 seconds, 1 minute 40 seconds, and 1 minute 20 seconds to reprogram, respectively.
Customize Headphone in the Headphone Casing
The flexible and portable form factor allows PortaChrome to be integrated into objects’ casings, such as the case of a headphone. This allows the user to reprogram the appearance of their headphones by keeping them in their case. Figure 17 shows three different designs that we applied to the headphone by placing it in its case, each taking up to 3 minutes and 52 seconds to complete.
DISCUSSION
We next discuss limitations of our approach and avenues for future work.
Automating Fabrication: To allow PortaChrome to conform to different surfaces, it is made from custom flexible circuitry on a textile substrate. In this paper, we present a fabrication technique suitable for fast prototyping using tools available in maker spaces, such as copper tape and a fiber laser, rather than optimizing for professional PCB fabrication. We validated two alternative fabrication methods for the LED circuits: (1) using flexible PCBs in industrial PCB manufacturing, and (2) using flexible LED strips for a DIY friendly process (Figure 18). We also tried automating the fabrication of the silicone diffusion layer. However, we cannot use SLA 3D printing for the diffusion layer since flexible SLA materials (Formlabs Elastic 50A) absorb UV light at 365nm, making them unsuitable for photochromic saturation. FDM 3D printing with clear TPU (NovaMaker) yields results that are not sufficiently optically transparent.
Non-Developable Surface: In order to conform to a non-developable surface, the entire PortaChrome device needs to be either stretchable or customized for specific geometry. While the stretchable textile substrate of PortaChrome allows for wrapping around non-developable surfaces, the rigid electronic components (LEDs) and flexible but non-stretchable circuit traces (copper mesh) currently do not support non-developable surfaces. Once the electronic components and circuit traces become stretchable in the future, the same PortaChrome fabrication workflow that we present in the paper can be used with the new stretchable components to make a device that can be wrapped around non-developable surfaces. Alternatively, researchers in graphics have also shown how to wrap non-developable surfaces with non-stretchable strips (Shape Representation by Zippables [29]). In future works, an editor can be developed to accommodate custom non-developable geometries and generate fabrication files for light sources of different sizes and shapes.
Color Evenness: A core requirement for reprogramming photochromic surfaces is to have a controlled irradiation of a surface with RGB and UV light. However, LEDs are approximately a point light source which produces the highest light intensity in front of the LED and decreasing light intensities on the sides. To mitigate this uneven distribution, we included a silicone diffusion layer on top of our LED matrix. While this improves the light intensity distribution, it does not lead to a completely even light intensity. In the future, we will explore optimization techniques for customized lenses that further improve on the light distribution [30] taking into account the specific emission profile of our LEDs.
Decoupling Activation Electronics with Color-Changing Materials: While electrochromic and electroluminescent materials yield higher frame rates and have lower energy consumption, photochromic materials make it easy to decouple the color-changing material (the photochromic object's surface) from its activation source (the light source). Separation of the activation source brings several advantages: passive material, such as photochromic dye, is easier to integrate into everyday objects than a full circuit; the modified color-changing object better preserves the original properties of the object, such as its weight, because all electronics are on a separate device; color-change can be made more scalable because the same activation source can be reused on different surfaces. Future research can improve the speed and energy consumption of photochromic color-change by developing brighter and more energy-efficient light sources.
CONCLUSION
We presented PortaChrome, a flexible and portable contact light source for reprogrammable multi-color textures on photochromic objects. To make PortaChrome, we presented the fabrication method to make textile-based layers of UV and RGB LED circuits and a silicone-based diffusing layer to achieve successful pixel images. Because of its flexibility and portability, PortaChrome can be placed in direct contact with the color-changing surface, allowing the light source to be attached to everyday objects and the color-changing process to be embedded in everyday user interaction. We demonstrate the new capabilities with four application examples, including data visualizations on textiles and dynamic designs on wearables.
We thank Kexin Wang for providing instructions on incorporating photochromic ink on textile, Yiyue Luo for conducting initial tests on diffusive textile patches, and Anthony Pennes for troubleshooting the circuits. We also thank Vivian, Regina, Katherine, Mairin and Alex for their help with soldering additional electronics. This work is supported by MIT-GIST Joint Research Program.
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PORTACHROME GRAPHIC DESIGN TOOL
While the control system (Section 5) allows the designer to initiate color change through an input color array, which can be generated based on sensor data, we also developed a graphic design tool that allows designers to specify the colors at each pixel location by drawing on a canvas (Figure 19). By clicking the "Turn on Brush" button, the designer can directly draw their design on a panel that displays a 12x18 hexagonal grid representing the pixels on the PortaChrome light source (Figure 19 a). Alternative to creating a design from scratch, the designer can also click the "Add an Image" button to import an image that is subsequently converted to fit the 12x18 pixel resolution PortaChrome currently supports.
Similar to other multi-color photochromic works, PortaChrome can only represent a subset of the CMYK color space due to the inherent limitation in available photochromic inks available today (PhotoChromeleon [17]). Thus, after creating a design, the designer can click the "Simulate" button to show the closest color achievable using the PortaChrome light source. After simulating the color, the user interface also displays the required texture transfer time (Figure 19 b). After finding a satisfactory color pattern, the designer can press the "Save Color Pattern" button to save the current design as a color array, which can be taken as input for the control script and subsequently transferred to the photochromic object (Figure 19 c).
1 https://www.safety.rochester.edu/ih/uvlight.html
2 https://github.com/HCIELab/PortaChromeUI
This work is licensed under a Creative Commons Attribution International 4.0 License.
UIST '24, October 13–16, 2024, Pittsburgh, PA, USA
© 2024 Copyright held by the owner/author(s).
ACM ISBN 979-8-4007-0628-8/24/10.
DOI: https://doi.org/10.1145/3654777.3676458