Expresii 寫意
  • Home
  • Showcase
    • Moxi Paint Engine
    • Yibi Brush Engine
    • A New Way to Paint
    • youji Rendering Engine
  • Download
    • Get / Buy Expresii >
      • Update Log
    • Sample Artwork Files
    • Third-Party
  • Support
    • Documentation >
      • End User License Agreement
      • Privacy Policy
    • Video Tutorials
    • User Forum
    • FAQ
    • Feedback
    • Help Translate
  • About Us
    • Contact Us
    • Media Resources
    • Privacy
  • Blog
  • 主頁
  • 示範
  • 網誌
  • 下載
  • 關於我們
    • 聯絡我們

Use Of Fluid Dynamics For Painting 流體力學的使用

26/7/2016

Comments

 
PictureCurtis' painting took 7 hours to render in 1997.
I know many of you are artists and may not be too aware of the historical development in the use of Computational Fluid Dynamics (CFD) for watercolor-like digital painting.  I think it's  useful to give a summary here.  

Cassidy Curtis  et al. was the first to apply  CFD    in watercolor painting  [SIGGRAPH 1997].  He used what is technically called Explicit  method (which requires taking small time steps) in solving the fluid equations. He was able to render one painting at 640 x 480 pixels in 7 hours on a workstation-class machine.​ At that time, fluid simulation was believed to be too slow for interactive applications. 

Two years later Jos Stam published a paper called Stable Fluids  [SIGGRAPH 1999].  He proposed to use a 'Semi-Lagrangian' method to solve the fluid equations so that large time steps can be taken in the simulation iterations to allow user-interactivity.  Because the implementation is simple and that he also released sample program for it, his method was widely spread. "Everybody can have his/her  own  happy meal and fluid sim",  so to speak.  At that time, usually simulation was done at a resolution of 256 x 256 pixels or lower.  

Later in 2003,  Mark Harris et al. adapted Stam's method to the GPU  for better efficiency.  Today,  maybe 95% of interactive fluid sim's out there (e.g.  this   &   this)   are based on Stam's work.  
​
Note that Stam in his  2003 paper  wrote:​
The idea of tracing back and interpolating which lies at the heart of the advect() routine apparently goes back to the work by Courant et al. [Courant52]. It has since then been rediscovered by many researchers in various fields and is generally classified under the heading of “Semi-Lagrangian” techniques. Parts of our work are also protected under U. S. patent # 6,266,071 B1 [Patent].
Above: A demo of Stam's 1999  fluid  solver.
​Below:  One of the many implementations by others.
acknowledging  that  what makes his solver special was actually something that had been done before.  While I'm not a lawyer, we are not sure if anyone implementing Stam's method for a profit would infringe their patent or not.  That might be one reason why many Stam's-based fluid sims we see today are mostly  'experiment' or 'toy programs' instead of commercial ones.

In 2003, our Nelson Chu started  working on simulating Eastern ink on paper.  He found Stam's method not very  accurate if large steps were taken to maintain 
Nelson's 2005 MoXi demo
interactivity,  so he looked for alternatives.  He  finally adapted a CFD method called Lattice Boltzmann  and the results were presented in his  MoXi  SIGGRAPH 2005   paper.  ​​ If you take a closer look, you will find that Nelson's method produces more realistic ink dispersion compared to that of a usual Stam fluid sim, the latter being more like smoke in space  than ink on paper.  After Nelson resigned from Microsoft in 2011, he continued to improve the simulation method and that's what went into Expresii you see today.
PictureWave-like behavior in Rebelle's watercolor sim
Another painting simulator featuring CFD is Peter Blaškovič's   Fluid Painter,  apparently  started in 2009  (judging from the earliest comment there).  Peter didn't state what method he used, but it looks very much like one based on Stam's without much change.  His other paint program Rebelle  that came out in 2015 doesn't seem to model watercolor faithfully  since the spread is like waves that bounce back and forth off the boundary (see above) and the results lack minute flow details. They might actually be using shallow water equations to model the flow.

The   Verve Painter by Taron came out in 2014.  Taron  also didn't state what fluid sim method he used, but if he based it on Stam's, at least he adapted the fluid density to volume and added shading, brush options, etc,  making impressive results possible. 

In around 2013, nvidia  entered the tablet market with their own mobile chip & stylus. With that, they also developed the paint app Dabbler (2014-2015). They modeled the viscosity of oil and the flow of watercolor but it's not clear if actual CFD was used for watercolor since the effect is mostly just blurring away the colors, which can well be done with burring instead of CFD.
 
Oh, there's one more:​ Adobe's new Adobe Sketch for iPad that came out in 2015.   Adobe licensed MoXi in 2006, but apparently they finally didn't really make use of our fluid code.  However, now you see this watercolor sim in this 2015 iPad app, whose effect is similar to what we had back in our 2005 MoXi, maybe somehow simplified since the flow is mostly an expanding motion and seems no free flow (see the Expresii video on the right) is possible. Adobe usually publishes paper on their research work (like in their previous attempt on watercolor, which uses some improvised physics and polygons instead of CFD), but so far we haven't found any documentation describing the tech behind this.  

Okay, that's all paint apps with CFD for watercolor-like effect that we are aware of. 

p.s. There were also attempts to use CFD for thick, oil-like paint simulation (e.g. Bill Baxter's), but that's another long story so we restrict ourselves to watercolor-like painting here.

Update 2016/10/22:  I think we should also show our Expresii here too, just for the record.  The video on the right shows Expresii running on a mobile device, namely a Windows tablet powered by Intel processors.
Above: Taron's  Verve Painter (2014)
Below:  Nvidia Dabbler 3.0 (2015)
Above:  Adobe Sketch's watercolor (2015)
Below: Expresii on a tablet (2016)
Comments

Expresii Officially Launched! 【Expresii 寫意】正式推出!

25/7/2016

Comments

 
Picture

Expresii is officially launched!!   (ノ´ヮ´)ノ*:・゚✧​

Download Expresii 軟件下載       (for Windows only)

It's been a long time. When MoXi was first unveiled in 2005, I was asked how soon it could become an actual product. I answered, 'could be two years'. In 2006, MoXi was licensed to Adobe, and I was even hired to do tech transfer. I was hoping MoXi would have good future there, but the story didn't evolve as I thought.  

Anyway, if they can't make it happen, we will.  

I know we all love free software but sorry that we need to start charging for the tool now (introductory price  US$59), since it took a lot of time and effort to create a tool with such advanced algorithms.  I think this is the most direct and healthy  way for Expresii to  grow without going down the path of showing ads or  telling you it's free but then charging you in  some funny way.  Your financial support would determine if small guys like us can survive or if we are left with tools coming from big companies only ​.

About Expresii

Expresii is a ground-breaking paint app featuring:
  • ​Yibi  Brush  Engine -  giving you power to create organic shapes like wielding a real brush
  • Moxi  Paint Engine   -  with fluid dynamics   bringing water-based paint sim to a whole new level
  • Youji  Rendering Engine -  allowing ultra-deep zoom with hybrid  vector-raster representation
The development of Expresii traces back to 1999 when Computer Graphics researcher Nelson Chu first designed a 3D deformable virtual Chinese (sumi-e) brush.  Subsequently he devised fluid-dynamics-based ink simulation, which was presented at SIGGRAPH 2005 under the name of  MoXi .  The MoXi  brush and ink tech was licensed to Adobe in 2006.
Expresii  is a successor of MoXi  developed   by Nelson Chu over the past four years  with improved simulation and rendering.  Expresii for Windows is now offered at an introductory price of $59 with trial license key  available.  

Notes to Users/Reviewers

Here are a few points we would like to make  sure you are aware of:
  • Expresii currently focuses     on mimicking Eastern ink painting/calligraphy only.   
  • Eastern ink   is similar to but not  exactly like Western watercolor.  e.g.  a drop of  watery paint  on most Eastern painting  paper s would absorbed and spread out immediately; on Western watercolor paper the drop   would just sit there without spreading.
For long-time digital painters, picking up Expresii requires some mind-shifting or getting used to:
  •  Paint with a Gradient -  In contrast to traditional paint apps, picking up of colors in Expresii is pressure-sensitive.  The harder you press, the color  goes more into the tuft. This way, you can get a multi-color loading similar to how you do it in real-life Eastern ink painting. Expand your skill set by learning to  use the side of the brush to paint with a gradient instead of one color at a time.
  • Economy of Strokes  -  Try to reduce the number of strokes you make.  More for less.  In Expresii, we make it possible to appreciate even one individual stroke.  
  • Rhythm is Everything -  in some  paint apps,  you may be  stamping  scanned  bitmaps of real  strokes.  At an extreme,  this is close  to  how a designer works where you position design elements to form a composition .  In Expresii, we want to promote another way of painting -  one that  is almost a   record of the movement of the brush driven by your hand.  It's gestural.  It's more like  a  serendipity where you can't create the exact same thing twice.
  • Choice and Chance - You  make some strokes  and let the wet ink  do its thing.   It's not just  simple put-that-color-there thing.  The ink reacts to your action and   could inspire your next stroke.  
  • Limited layers -  Currently Expresii  only supports two layers.  We'll  support for more layers in the future. In the meantime,  the Snap-Down (rasterizing) to  Underlay  acts as a  temporary    solution when you run out of layers.   Given only two layers, we usually do linework   on one, and color/fills on the  other.
To tablet users:   Expresii is not yet optimized for tablet use yet since  for quick operation, you still need a keyboard.  In addition,  most tablet computers  today still don't support pen tilt sensing.  For now, we recommend  using a desktop with a graphics tablet  that supports tilt sensing. 

​重拾筆的感覺

現在一般繪圖軟件,思想較近西方傳統,’brush'  一般就是用來‘塗’的,比較像‘刷子’。但東方毛筆是書寫工具,經多年發展表現力尤佳,東方繪畫的基礎訓練是書法,其正是要訓練操控筆的能力。在我們Expresii 軟件裡,您可以重拾筆的感覺:透過手的動作自然地做出不同的點、線、面。Expresii 的筆,也是眾多繪圖軟件中,最能充份利用帶側鋒感應的專業級電繪筆的。
Picture

水墨淋漓 

當然還有我們的水墨。我們是應用了流體力學來模擬水墨流動,以做到目前為止世界上最自然的實時水墨效果。
We use  Computational Fluid  Dynamics  for our ink flow simulation to give you the most  natural results. ​

突破像素局限

現在的繪圖軟件還有個問題,就是圖不能放很大,放太大會看到一粒粒的像素。 所以我們一再革新,用混合向量像素(hybrid-vector-raster)的方式來儲存繪畫數據,讓Expresii 的圖可以放很大。
​We  use  a novel  hybrid-vector-raster   representation to allow  high degree of zooming in.

作者感言

老套點講,製作Expresii 真是嘔心瀝血。現在終於正式推出了,儘管還有不完善的地方。

感謝【狐朦大叔】作者Tom 一直支持。他也剛出書了(用Expresii 畫),感覺是一起生了小孩。還有感謝一直支持的Shuen Leung, Mark Lam, 日本的 Kuroda-san ,和盧生、李生和最近認識的飯主等前輩的經驗分享和幫忙,還有Wacom 台灣總經理Martin的推介和其他高層的賞識,和其他曾經給予鼓勵支持的朋友。
​
從美國辭職回來已五年,也一直沒收入五年^。長期沒收入,在亞洲社會是很難理解的(一直以為李安只待家兩年,原來六年才對),我前幾天還真的被問 ‘還未找工作?’,也曾被問回來後悔否。其實在哪發展最好,難說,但肯定的是,在這邊比較近父母,還有可以在外婆的最後幾年多點看她。

2002年去北京發表虛擬毛筆的論文,時年二十五當是個交代。現在趕在四十歲前把Expresii 推出了,也算是個交代。我的青春都放在這電腦繪畫的研發了。 作為一個東方人,我覺得有責任去把我們最好的東西,承傳並發展下去。筆有千秋業!

-  Nelson Chu
2016.07.24
^ 感謝去年澳門的學會請我演講給了點講費,幾年前香港Poly 的Wilson 找我也有一點點講費
Comments

Tackling The Fat-Pixel Problem 放大時可以不見像素嗎?

8/7/2016

Comments

 
Today, often   digital painting  s are done in less than 4k resolution, and you might be further limited to e.g. 2k when you use   computationally-intensive tools like Corel Painter's watercolor. If you zoom in, you will see big fat pixels.  You can't  print it large  -  it looks fine on a computer screen but printing it  on a piece of paper  would  make the resolution  insufficiency prominent.  In fact, even our screens are  getting higher and higher resolutions.  In 2007 ,  Sony showcased a 4k  projector as a  very advanced piece of equipment - but now it's no surprise if you see a 4k screen around, be it desktop or mobile. We're more urged to address the resolution hunger than ever.

A Pure Vector Approach as Solution?

In late 2014 the new painting app  Mischief   made a splash  being acquired by  The Foundry.  Mischief's infinite zoom  is their core competence over  other painting apps. However,  infinite zoom has always been a feature of vector-based representation - and   Mischief is in essence  a vector program.  The issue was just that most previous  vector-based  tools are more like  a designer's  tool rather than a painter's making it hard to do painting fluidly. BTW, infinite canvas is also not new, as at least Rita offered such feature years ahead in 2006 and is vector-based too. 
PictureMischief's vector strokes. Now where's the promised painterly quality?
Like in most vector-based tools,  the lines made by Mischief are crisp (except for the one brush that gives a dithering effect, which is another kind of  crispness if you will), which is good for line arts or sketches.  But if you regard the artwork as  a 'painting',  these lines are  too clean.  You can add more strokes to get more painterly, but with too many lines the system would slow down  as  details created by    every line  has to be redrawn every time you pan your screen - even with the advanced   Adaptive Distance Field (ADF) tech   behind it and that it is said to utilize the GPU for accelerated processing.  ​​Technically, if the number of strokes is N, the redrawing is of order O(N). *  

Previously we covered Adobe's vector approach to do watercolor on the ipad  in this blog entry.  Essentially it also  looks good on spec, but not that great in practice. When enlarged, you see many individual polygons overlapping each other (below). Personally, I don't think it looks too pretty nor natural, not to mention the added burden of rendering thousands of polygons.  ​(๑´╹‸╹`๑)
Picture
Picture
Adobe's solution for hi-res rendering with their 3D brushes (images from [1])

A more Painterly Approach

In Expresii, we take a rather different approach  to the fat-pixel problem.  Our  representation is somewhat between  pixel- and vector-based.  If  the  canvas/paper  resolution  is  M, our redrawing  is of order O(M), independent of N.  This is a property of pixel-based tools. However, our magic is that we are able to zoom in a lot - a lot more than what  existing   pixel-based programs  offer given the same amount of paint data.  We may call this ' ​Good-Enough Zoom' (vs.  Infinite Zoom).  This is somehow akin to audio sampling  -  our ears can only hear up to 22KHz  so sampling up to double of that namely 44KHz is 'good enough'.  In real world  painting,  someone might draw a tiny figure, but he or she is not likely to add every detail to that figure.  As a viewer, if you can zoom in  so that you can see the fibers in the paper,  that's pretty enough too.  

Do we  need infinity zoom?  For cases like showing  the world reflected in  a girl's eye, yes.   For such cases, people without infinite zoom could simply make drawings at multiple scales and switch between the drawings  (which is what people currently do) so it's not really the end of the world.

In Expresii, we don't claim to do everything.  We can't do infinite zoom.  Our canvas/paper is finite, which is  actually closer to a real-world painting experience - you have a frame to anchor your work.  Instead of infinity canvas, Expresii  offers extendable paper.  Our end result is a  rather organic looking painting that we can zoom a lot into.  The strokes and flows are extremely  natural   -  unprecedentedly   natural. 

GPU Acceleration

Not only our ink flow simulation utilizes the GPU power.  Our rendering  engine (which we call Youji  有極 for marketing purposes ;-) is also GPU accelerated.  Given a decent graphics card, you can pan and zoom silky smoothly.

BTW, we are really glad to see a steady growth of GPU hardware. We used to require an expensive discrete graphics card,  but now even an integrated GPU  can do the job fast enough. Interesting side note:   When Nelson  was speaking at the Adobe Headquarters in San Jose back in 2006, a Senior Photoshop Scientist was bashing the use of GPU.  I think he was like laughing  at a person building the Internet at its early stage - hey network is so slow, why bother.  Well,  if you can see the potential early, you will be heading in the right direction.  Now, even  Photoshop itself is getting more and more GPU acceleration. 

Best of both Worlds

Articles about Mischief often praised it taking the best of both worlds of vector and raster. Mischief promised  'the richness of pixel-based brushes'. Yet in reality we don't really find the promised richness of textured brushes like those in Corel Painter or Photoshop. Furthermore, operations like smudging or blurring, which are trivial for raster-based tool s, are not possible or at least the maker still can't demonstrate such possibility^.  ​

In contrast, Expresii really gives you the richness of pixel-based tools. You can still blur a stroke (we don't have a separate blur tool but you can do so by stroking with a clear brush or use our new Pusher brush mode), not to mention our extremely natural ink flows efficiently executed on the GPU all thanks to its pixel-based nature. However, Expresii also has its vector personality - you can zoom in a lot as if there's no pixels.  We believe Expresii is a true innovation in the history of digital painting, really  'taking the best of both worlds'. Give it a try today and see for yourself!
Reference:
[1] from their paper "Industrial-Strength Painting with a Virtual Bristle Brush", 2010. [cached copy]
*  In ADF there is only one distance field to be sampled but the sampling needs to be more refined  when a new stroke comes in, thus causing the complexity to be O(N).  However, in practice Mischief is performing quite fast even with large number of strokes.
​

^  Update 2016-12:   development of Mischef seems to have stopped.   
Founder and Chief Scientist   Sarah Frisken   even left the new company founded  due to the Foundry acquisition.  Head of that company  Chris Cheung , who moved from Autodesk's Sketchbook, also left the company.  Update 2019-10:     madewithmischief.com is finally closing in Dec 2019.
Comments

Why Go Digital? 電腦繪畫有什麼好處?

7/7/2016

Comments

 
PictureDigital Work printed on Chinese xuan paper 數位畫打印在宣紙上
I was recently  asked  why  one would want to paint  digitally. The two most common reasons are: 
  •  Convenience   (can undo, save copies  at different stages, no setup and cleanup time, already in digital format) 
  • Cost reduction (no worry for wasting art materials)  

​And what are the cons of digital painting?  Long time ago, I discussed with Wucius Wong on this.  Wong suggested two main  concerns:
  1. Lack of physicality  
  2. No  tactile feeling of using a brush  on paper  
For 1,  printing the artwork on real paper somehow  solves the issue.  For 2, I would leave it to hardware makers.

As a software developer, there's still things we can do.   We'll discuss digital painting tech  innovation in  our next blog entry.

還有就是,畫家如果靠賣畫為生,傳統畫較易賣高價。相反數位(digital)畫,大家覺得打印出來的沒那麼有價值。其實打印出來的東西也可以賣高價,如罕有的郵票。還有傳統版畫,也是重複印出來,但通常限量,畫家每幅記號並簽名。大家大不了就把你的電腦畫用最高檔的(抵擋的放久了會褪色 >x<)墨水打印出來並簽名,然後把原檔刪了就可以'物以罕為貴’了。

Ease of change - good or bad thing? 容易修改熟好熟壞?

PictureWucius Wong & Nelson Chu. Photo by Shuen Leung
Wucius Wong   is one of the few senior (Chinese) ink painters who does make use of computer technology.   He exclaimed to Nelson  - it is too easy to make changes in your digital art!

​王無邪 (Wucius   Wong) 是少數很關心我們Expresii 開發的傳統畫家,他自己也很早就有用電腦輔助作畫。他說我們用Expresii作畫,太容易修改了!

It's true that in traditional  ink painting, it's much harder to make afterthought changes and thus  masterpieces don't come by easily.  But when it is easy to make changes, one might be trapped to spend too much time keep making changes.
​
傳統繪畫難修改,所以精品難求。但就純粹作畫者來說,容易修改應該是一個優點。但這‘優點’有時就帶來更多‘麻煩’ --  就是改來改去,一幅畫拖太長。

有趣的是Wucius  也講過^ Interestingly Wucius once said^:
When the painting is still there, there's always a temptation to adding a line or a dot to it. I think all artists would do the same thing naturally.
大家也有改來改去的煩惱嗎?以下我也是因為電腦畫太容易修改,所以改來改去。老人耳前的髮絲,都很多考量。畫粗一點好像較好表達老人‘幹活’的情況,畫細一點優美點但會不會給人太年輕的感覺?

If you're a digital painter, do you find yourself keeping changing little details  in your art pieces?   For me,  for instance, I kept changing details on the hairs in from of the ear, trying to find a look that better represent this old lady:
Picture
Picture
有人說一幅畫磨太久,不如把時間花在下一幅。Some say you should spend time on your next piece rather than lingering  on your current one. Anyway, here's the Old Lady 'final' version:
Check  out a video showing  the  process of creation:
^  In video 'Mountain in the Mind', Minneapolis Institute of Art,  1986.
Comments

    Expresii 寫意

    Previous Posts
    以前的文章

    November 2022
    October 2021
    July 2021
    June 2021
    May 2021
    April 2021
    March 2021
    February 2021
    December 2020
    November 2020
    October 2020
    August 2020
    June 2020
    April 2020
    January 2020
    December 2019
    November 2019
    October 2019
    September 2019
    August 2019
    July 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    September 2018
    July 2018
    June 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    October 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    February 2017
    January 2017
    December 2016
    November 2016
    October 2016
    September 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    October 2015
    September 2015
    August 2015
    July 2015
    June 2015
    March 2015
    February 2015
    January 2015
    December 2014
    November 2014
    October 2014
    September 2014
    August 2014
    July 2014
    June 2014
    April 2014
    November 2013
    October 2013
    July 2013
    February 2013
    January 2013
    December 2012

    Categories 分類

    All
    3rd Party Tool
    Animated
    Artists
    Calligraphy
    Demo
    Hardware
    Mac
    New Feature
    Publicity
    Purchase
    Surface
    Tech

    RSS Feed

Picture
© Expresii.com 2023. All Rights Reserved.