adrienlucca

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Tag: math

Light transformer prototype v 4, proof of concept

wall

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The key was to build the mathematical solution for this (that would be easy for any mathematician I guess…) And that’s it! Still quite bad programming (“functionnal programming”), but good work!

Take this picture:

MAP

Okay it’s not a “real” picture, but it could be: imagine that this is a precise representation of the amount of light that falls on a wall, the wall having the same proportions as the picture. The value of every pixel is proportional to the amount of light on the wall.

It is possible to take such a picture, one needs a properly calibrated digital camera. The result is fairly good if one has a good solution to remove the lens “vignetting”, and to check if the CCD or CMOS reacts properly.

So let’s imagine — for now — that it is the case: the picture is an almost perfect one, it is the map of the intensity of the light on the wall, coded in 16bit greyscale (values in the range 0 – 65535), and the exposure is good: no value is equal to 0 or to 65536, all the data is properly recorded witout being truncated.

We have a list of 386 color samples coded in RGB, printed with a very good inkjet printer. These color samples are measured by a spectrophotometer, i.e., we have their curves of absolute reflectance. We also have the spectral distribution of the illuminant (a fluorescent tube for ex.) — and we can use some Color Matching Functions to convert our spectral data into a colorimetric language allowing additive color calculations (CIE XYZ)

refl

ill fluo

XYZ

 

With all this, we are ready to calculate what sould be printed on the wall in order to get a uniform light field of a unique color, and the picture starting this post shows how the wallpaper could look like, before being printed (it is one of the infinite geometrical suitable solutions, using random numbers to distribute colors)

This is not only a simulation, all has been computed, only the wall’s image is a fake. That’s “painting with paints and lights”, the beginning of a long story I hope :)

A few more spectra (just a bit!) :

few more

macro photo on D65 6.1

macro D65 6 2

macro D65 6.1 1

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a good junction

DSCN0038 copie

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To have a good (near invisible) junction between two triangular zones means succeeding, with different lines boldness and angles, to cover the paper with the same proportions of colors. If it is visually good, it means that the drawing instrument is well calibrated, and that all the calculus were correct.

In my next drawing D65 n°6 I will have a lot of junctions like this one, the challenge will be to make them all as good as this one! :)

Just to try, a mixed color synthesis process

grey sample adrien lucca plotter june 2013

A grey color sample in mixed additive/subtractive color synthesis

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You might have heard of the “additive” and “subtractive” color syntheses at school or anywhere else before.

When I was an art student, the difference between the two syntheses of color was explained to me in terms of difference between “material colors” and “colored lights.” The two canonical examples were the computer screen’s RGB and the offset CMYK color systems.

I have never been satisfied by these explanations and examples. My fist-ever counter-argument was simple: a screen and an object under a light source both emit light in the direction of my eye, so why make a difference between two types of objects that both emit light?

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How I abandoned subtractive colors

Since then, I have been trying to create a (material-) color process that would be as easy and as precise as the union of an image editor and of a computer’s screen, but on paper (see my series D65 studies, 2011-2013.)

In 2009, I decided to abandon the use of any transparent colored material (inks, watercolors, etc.) because there was for me no precise way to control the amount of material that I would put on the paper: if you put more ink it makes a thick layer when it dries, which appears darker than a thin layer.

Also, transparent inks produce quite unpredictable colors when you superimpose them…

Color averages (additive color) on paper

To control additive color synthesis is a much simpler process: imagine yourself with a piece of white paper and a opaque black paint, if you can cover almost exactly 1/2 of the paper with small black dots, black lines, a checkerboard or anything that diffuses evenly enough the black on the paper, the resulting color of this object – optically – will be in-between black and white, namely a grey optically made of 1/2 of these white and black materials.

Such a mixture has a simple meaning, but how would you find a 1:1 mixture of black and white if you were mixing paints? What would 1:1 mean? Without a model of human vision, nothing.

grey detail

Magnified view of the 1st picture : it’s hard to see but there are 8 colors

Combining addition and subtraction

The advantage of using opaque colors was the easiness of creating an additive color process on paper (making color averages.) However, if we possess a tool that can pour on paper transparent colors evenly, we can include the transparency of the colors in the process. A true mixed process is then created, with 3 primaries on white, we get 8 colors already.

Of course, this is not any different than the traditional quadri offset process!

model mixed color synthesis

If we already measured the colors resulting when superimposing the primaries, we can predict the appearance of such color-mixtures with basic equations, where 3 variables x, y, z, refer to the amounts of the 3 primaries (tartrazine yellow, quinacridone magenta, phtalocyanine cyan)

However, it seems quite unstable for now and much harder to calibrate than my previous additive process.

second plotter’s proof of concept

proof 2 13 June 2013 Adrien LUCCA

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The problem was: the plotter makes dots from left to right, line by line, then goes to next line, etc.

It was a problem because one could see these lines and their limits/visual artefacts, when the pen’s paint flow slightly rises up or slows down.

How to solve that? I just programmed the drawing such as every point is made in a random order, and then: magic! everything disappears (see the video).

D65 n°3, transparences / lampe / spectres, 2012

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Below, detail: desaturated daylight spectrum

Planck’s blackbody colors (first layers)

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This is a new thing.

For the moment I just did the first 2 layers of paint (depending on the case, Titanium White + Ultramarine Blue, or: Titanium White + Cadmium Yellow light,) – there are 2 left.

In the squares will be the average color (50%/50%) of the color of my background and of the colors of the planckian balckbody locus with temperatures from 4000 K° to 9500 K° – as given by these (approximative) formulae in the CIE UCS 1960 color space:

 

I choose to make these samples with the same brightness as my backgound, so only the color difference is visible. None of them is neutral grey because I’m working with illuminant D65 (my “white point” is there…,) which is not located on the planckian locus, but slightly blue-grennisher (see below)

The locus in the CIE UCS 1960 color space (after wikipedia)

D65 n°3 part II starts

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I’m gonna do a “lamp simulation” (a circular gradient with constant tint and varying brightness, based on the abstract model of a “perfect lamp,”) based on 11 colors: 3 times RGB with 3 levels of brightness (I dont enter into the detail of how I choosed them) and Black/White.

hi-resolution pictures of the prototype

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Light ON/OFF, hi-resolution orthographic panorama made with Hugin.

For me, there’s not much difference between such a work (the prototype, made of laserprints on paper) and a “traditionnal painting.”

I’m really starting to think it’s just the same thing, like Richter includes amateur photography in the field of “painting.”

about to end

The central part being equalized.

Something is slightly wrong – the values are increasing where the light is intense -, but it’s still very close to what I wanted (an equalized luminance everywhere in the rectangle).

good & bad news :)

The bad news: the laser printer cannot handle large black prints, some unit of the printer makes a random glossy layer on it.

the random gloss

the (very) good news id that the luminance correction is not very angle-dependant, means that except for that random gloss, the correction works at a wide variety of viewpoints, that’s really nice.

from the left side, the gloss dissappears and the flat is still “flat.”

below: zooms on different parts from the left side (same shutter speed)

wall to be visually uniformized: “ganzfeld” prototype

I will try to create a “ganzfeld” on this wall by subtracting light (using black printed patterns.)

This is the object of my residency at Netwerk, Aalst, BE, from last Monday to next Saturday.

More documents will come…

D65 lighting prototype @ JVE, Maastricht – 2011

D65 Normlicht light tubes mounted with an aluminium reflector

 “Table-Tops Room,” Jan van Eyck Academie, Maastricht, NL, 2011

D65 #3 1st “fake lamp”

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