Extra Polynymous
I received a comment with a great idea: try to hide images in pairs of lithophanes! Lithophanes are thin sheets of an opaque and translucent material with varying thickness that display an image when held up to light. The image is bright where the material is thin, and dark where the material is thick. Previously, […]
Previously, I used polarized sheets to generate images. That’s too complicated to physically make, so it’s time to try something else. How about just two transparent films with black marks? Then we can try to encode four images that are revealed by overlapping the two, and rotating the top film. This sort of rotation problem […]
Have you ever played with polarized films? If they’re aligned, they look transparent. If they-re misaligned by 90 degrees, they become opaque. Let’s use this to make pictures! The intensity of transmission is governed by Malus’s Law, which says that the intensity is , where is the misalignment of the two films. Now how can […]
Previously, I used single-frequency Fourier noise to do some halftoning. This time, I’ll use broad-frequency noise. I’ll filter 2D white noise with a gaussian with standard deviation . This reduces the high-frequency content. Let’s call the filtered noise , and the gradient-scaled version. Skipping all the tedious probability work, the pdf of the gradient-scaled noise […]
One way to do stochastic halftoning is to draw contours of noise functions. For example, you can make 2D single-frequency Fourier noise, and draw a contour wherever the noise crosses the zero-level. If you do this with wavelength L, over an area of A, the total arc length turns out to be very nearly 2.2*A/L. […]
In a previous post, I deformed a grid of lines to halftone an image. I wanted to do the same thing with a checkerboard, but I figured that it would be similarly difficult and would require optimization. So I used the same optimization framework with a checkerboard, applied it to a brightness ramp, and found: […]
Imagine that we have a screen door, and we want to push around the wires to make an image. It’s not a simple problem! There’s a fixed number of wires in each direction, so how do we properly distribute them? Let’s define a pair of phase maps for x and y, and . We’ll draw […]
The Joukowski transformation is a great way to study basic airfoils using potential flow. It gives a nice way to derive the Kutta condition, as well as the classic lift slope . But in all those demonstrations, I never saw the lift and drag curves of the Joukowski airfoil! Luckily, I have XFOIL to remedy […]
Sometimes you want one picture to have the color scheme of another. This is called color mapping or transfer. When I was making the rearranged images, I was concerned that I would get bad matches if I didn’t make sure the images were similar enough. It was helpful to ensure that their brightness histograms matched, […]
Let’s halftone an image with some overlapping wiggly spirals! I want to draw N lines, spiraling out from the center of the image, and have them each slightly offset. With the proper offset, this will create the (approximately) proper darkness. With image darkness k, line width w, and line spacing L, we can get a […]