WangLu's Notes

In January, as part of the preparation for digital painting training, I calibrated my laptop display and my pen display. Yet in April I realized that images look quite different on my laptop, on the pen display, on my phone or on others' devices. After hours of research, trail and error, I managed to learn more principles and calibrated my hardware and software. Here are some notes: 1. Colorimeters are not spectrometers. Instead of measuring the full (visible) spectrum, the main goal is to simulate a standard observer (with three color receptors), or XYZ values. 2. Due to #1, there are assumptions made here and there to cut down the cost without hurting the quality too much. However an important aspect is the type of monitor (e.g. WLED, WLED+phosphor, GB LED,  RGB LED, OLED etc.).  The chracteristics of each type is diffrent, mostly on the "base spectrum". The calibration may look off if the wrong correction matrix is used. Note that old colorimeters might not support new...

Gamut masks, or gamut mapping, is a color managing tool made popular by James Gurney . It is a set of practical instructions, which allows us to easily create a palette of harmonic colors. James has explained the method in various formats: 2008 blog post 2011 series 1 , 2 , 3 Video  on Youtube. His book Color and Light: A Guide for the Realist Painter I found this method so inspiring when I first learned about it around 2014. Recently it came back to my mind when I started developing the digital Zorn palette , which turned out to work quite well . I decided to revisit the cool method, in the hope of getting better understanding the method and some color therories. The goal includes: Recognizing the limitation of physical paints. Figuring out an idealized model of the method. Adapting the method for digtal painting. The Original Method I'd summarize the original gamut mapping method as the following 3 steps: Start with a color wheel. Maskthe color wheel with a simple shape, typicall...

Update: the palette for Krita is available here . For beginners, limited palette is a useful tool for learning to use colors. Among many of those, the Zorn palette, used by Anders Zorn, seems popular in some ateliers. There are a few variations of the Zorn palette. The version that I'm learning consists of the following base colors: Ivory Black Permanent White or Titanium White Yellow Ochre Cadmium Red Light When painting, you are only allowed to obtain colors by mixing these base cases. Depsite of its simplicity, the palette is surprisingly powerful, especially for portrait painting. Since I'm learning both painting and color theories, I find it interesting to make a digital version. Mixing Paints The process of mixing paints is rather complicated . It is somewhere between additive-average and subtractive. However the situation is simple because the Black and White has very few chroma, and the Red and Yellow are very close in the color space. In this case we could get quite go...

Before the digital era, the Munsell Color System  was probably the best perceptually uniform color system with hue, chroma and value components. It is also used nowadays. The 1943 Munsell renotations (with portion cut away). Source: Wikipedia   CC BY-SA 3.0 When reading the introduction page of Oklab , I learned about the idea of projecting Munsell colors into diffrent color space. I find it an intuitive and fun way to study color space. Who does not like colorful demos? Here we have to assume the quality of the Munsell data, which might not be 100% scientific. Anways I think it should be good enough, as proved by generations of aritist. With this assmption, we may examine munsell colors in the target color space, and observe the following: - Do the points with same chroma form a perfect circle? Are they distributed evenly? - Do the points with same hue form a straight line? Are they distributed evenly? - For luminance/brightness, actually I assume decient color spaces ar...

Previously  I discussed why HSV and HSL are bad, despite that they are quite popular adopted by digital painting tools. I learnd about HSY from Krita, which seems to solve a number of issues. Here I did some quick explorations in order to learn more about it's properties. First of all, HSY is very similar to other HS* family members. The definition of H and S should be the same as in HSL. Y is for Luma, which is a weighted sum of (gamma-corrected) all three components. The weights reflect our brightness sensitivity of different wavelengths. The specific values depend on the actual primary colors. Here's a HSY disk at Y=0.5, for sRGB. HCY disk with Y=0.5 Comparing with HSV or HSL disk, this one looks smoother, and a bit "muddy" near the center. This means the Y value does predicts the actual luminance well. The gray version (converted via CIELAB) may verify this observation: L(CIELAB) channel of the HCY disk. So there is a huge improvement over other HS* models. It see...

The first time I heard of the term "color space" was probably from some article about display color gamut/calibration. I learned that it is important for a display to achieve at least 100% sRGB, for digital painting or image processing. Well I didn't know what exactly "s" means here, but I got a feeling that it has something to do with the RGB values in HTML color codes. A few color spaces Source: Wikipedia   CC BY-SA 3.0 The diagram could be very confusing. I had a few questions, which I think I can answer today: Why does it look like a weird 2d shape, instead of a 3d volume? It is a 2d shape, which is a slice of the 3d space at a constant luminance. More specifically, this is a sliced xy space at a specific value of Y. Why does the sRGB color space appear as a triangle? The sRGB color space is generated by 3 primary colors, which corresponds to the 3 vertices of the triangle. Moreover, for any 2 colors, all available colors obtained by mixing these 2 colors (w...

Palette and Color pickers The word "palette" typically means a set of colors to choose from. In the digital world it means something similar, especially on older systems which support very small number of (e.g. 16, 256) colors. The first "advanced" color picker I saw was propably the color picker in Microsoft software, e.g. Paint, Word etc.  Color Picker in Microsoft Windows, which has not changed much since Windows 3.1.  At the time I was very excited by the colorful UI, and I had lots of fun exploring the colors. However, at that time I barely understood the numbers for red, green and blue, and by no means did I understood the other set of numbers: hue, sat and lum. Later I came across this "ring + triangle" or "ring + rectangle" color pickers, mostly in digital painting software.  HSV Color Picker in Krita At that time I didn't fully understand the differences of V, B or L, neither did I understand the differences between the rectangle ver...

In my childhood I learned about the three primary colors: red, yellow and blue. They are "primary" because any other color may be obtained by mixing these colors, on the other hand the primary colors cannot be obtained in this way. Years later I learned about RGB and HSL for UI and digital painting. At that point I thought I've got a solid understanding of the colors, until now. Having been learning color therories for a few weeks, I realized that how much I do not know about colors. This is the first study notes on color theory, which lists a few misconceptions that I have had for years. Color is a physical property of lights or objects. Right? Right and wrong. When we say "the apple is red", we actually mean "under the standard daylight illuminant, the spectrum reflected by the apple is perceived similarly as other objects that are commonly known as red". The light source and the spectral reflectance are apparently important, yet the observer is also...

configure softwares gimp: edit->preferences->color management->try to use system monitor profile firefox: about:config ->  gfx.color_management.mode -> 1   test pages http://www.gballard.net/photoshop/srgb_wide_gamut.html http://photographylife.com/is-your-browser-color-managed I bought a spyder 4 express and would like to try dispcalGUI on my surface pro, so I have to install Argyll CMS's driver, which is not signed. For windows 8, one option to disable driver signature enforcement is through "advanced startup settings", which lists a few options after a restart, and you can press f7 or 7 to disable it. However for my surface pro, it refused to recognize my keyboard, no matter it is a bluebooth keyboard, a usb wireless keyboard or a normal usb keyboard. I guess a touch/type cover might work, but I don't have one. Another option is to enable test mode (bcdedit -set testsigning on), before which you should also disabl...