Governance by those who do the work.

Tuesday, December 21, 2010

Marbling the Torus


I have cleaned up the math on Marbling the Torus and changed my scripts to oversample the images, resulting in less graininess.

Sunday, December 12, 2010

Tuesday, November 30, 2010

Modeling Ink Drops

Added to http://people.csail.mit.edu/jaffer/Marbling/Dropping-Ink.

... given a point P and a new ink drop of radius r centered at C, move the point radially from C to:

C + (PC) · sqrt(1 + r2
||PC||2
)

One correspondent complains that, because the divergence of this transform is not zero, it can't be incompressible.

Divergence is defined for a continuously differentiable vector field. But this transform is not continuously differentiable around C; thus its divergence isn't well-defined. The common definition of incompressible is in terms of the divergence of a vector field. For a vector-field where the divergence isn't well-defined, the definition is silent.


However, I can show that this transform preserves the area of all neighborhoods not containing C. Consider the annulus centered on C having inner radius sqrt(a/π) and outer radius sqrt((a+b)/π). Its area is b.

If ink is injected at C forming a new circular region centered on C having area e, the annulus having area b will expand to have an inner radius of sqrt((a+e)/π) and an outer radius of sqrt((a+b+e)/π). The area of the expanded annulus is still b. Note that the expanded annulus is thinner than the original.

Because this transform is radially symmetric, any annulus slice with sides forming angles with C of θ and η will map to the expanded annulus slice between the angles of θ and η. Because the annulus and slices can be made arbitrarily small, all neighborhoods not containing C map to regions having the same area.

ICC Profiles

From http://people.csail.mit.edu/jaffer/Color/Dictionaries:

Section 10.14, "namedColor2Type", of Specification ICC.1:2004-10 (Profile version 4.2.0.0):

The namedColor2Type is a count value and array of structures that provide colour coordinates for 7-bit ASCII colour names. For each named colour, a PCS and optional device representation of the colour are given. Both representations are 16-bit values and PCS values shall be relative colorimetric. The device representation corresponds to the header's "colour space of data" field. This representation should be consistent with the "number of device components" field in the namedColor2Type. If this field is 0, device coordinates are not provided. The PCS representation corresponds to the header's PCS field. The PCS representation is always provided. Colour names are fixed-length, 32-byte fields including null termination. In order to maintain maximum portability, it is strongly recommended that special characters of the 7-bit ASCII set not be used.

This namedColor2Type specification dates back to version 3.2 (1995), perhaps earlier. Only XYZ and L*a*b* colors are supported. Although version 4.2 defines "multiLocalizedUnicodeType", namedColor2Type is restricted to ASCII (and length less than 32.B). The colors in this table are specific to the profiled device. So namedColor2Type appears to be intended for including "spot" colors (such as from Pantone) in a device profile, not for device-independent color dictionaries.

Tuesday, November 23, 2010

XKCD Color Name Dictionary


New on my Color Dictionaries webpage, XKCD Color Name Survey.

XKCD's 2010 color name survey is similar to the Color Naming Experiment. Rectangles of RGB colors on a white background were presented for the subject to name.

Compared with Color Naming Experiment, XKCD has better coverage of the darkest octant.

The catalog compares XKCD with CNE. Most of the darker shades common to both dictionaries are darker in XKCD. Greens seem to be overrepresented, probably a result of generating samples from a color-space which is perceptually very nonuniform.

With its larger set of dark colors, the XKCD Color Name Dictionary surpasses the Color Naming Experiment dictionary (and X11) for surface colors, although a large portion of its colors will not print faithfully.

Tuesday, November 9, 2010

New Color Dictionary

New on my Color Dictionaries webpage, US Federal Standard 595C. Although not a general-purpose source, these colors are of use when rendering post-boxes (15050), school-buses (13415), flags (UN Flag Blue 35250), signs and military clothing and equipment.

Monday, September 6, 2010

Simulating CoolRoofs



The SimRoof program I have been developing can now simulate the thermal performance of horizontal cool-roofs from the measurements made by coolroofs.org.

For more, click on the graph.

Wednesday, August 11, 2010

Argiope aurantia


This spider at about 4.cm is the largest I can remember seeing. It has an interesting zigzag pattern in its web.

Friday, July 30, 2010

chipping-sparrow chicks


chipping-sparrow chicks, originally uploaded by aubrey_jaffer.

Here are three-day-old chipping-sparrow chicks. The nest is in a yew(?) bush in a neighbor's yard.

Saturday, May 29, 2010

West meets East

2500 years ago, Buddha, sage of the (warrior) Shakya clan, taught:

All is impermanent.

65 years ago, the warrior sage of the MacArthur clan answered:

There is no security, only opportunity.

Wednesday, May 5, 2010

Storm clouds


IMG_2160, originally uploaded by aubrey_jaffer.

The sun was shining brightly behind thunderheads.

Sunday, March 7, 2010

Color Name Dictionaries

Newly expanded and updated, Color-Name Dictionaries is my most popular webpage, averaging 150 visits per day. It is linked from Wikipedia and elsewhere. Chirag Mehta has created a Name that Color webapp using the Resene Paint Colours list. There is even a Color Dictionary iPhone app based on the NBS-ISCC Centroids and Dictionaries of Color Names.

Unfortunately, Color-Name Dictionaries has not been noticed by the X.Org Foundation nor the World Wide Web Consortium, whose products contain deeply flawed color dictionaries from the 1980s. Instigating change in the face of so much organizational inertia is a daunting task.