lozano

Colour and Appearance in foods

Lic. R. Daniel Lozano AIC 2010 Color and Food, Mar del Plata, Argentina, 12-15 October 2010

Visual Appearance

Is a much more complex phenomena than colour.

When a person looks a scene, perceives size, shape, colour, gloss, texture, and other forms of appearance.

Gloss, translucency, transparency, clarity, haze, pearliness, metallic, iridescence, luster, texture, etc., are ways to describe it.

Known process implies many aspects that start in the luminous signal to the unconscious remembering of lived images.

“Total” Appearance as John B. Hutchings proposed Total Appearance has three items:

Inherited and Learned responds to specific events (culture, memory, preference, fashion, and physiological and psychological effects).

Receptor Mechanisms: colour vision (including adaptation, afterimages, constancy, discrimination and metamerism). aging effects (cataract, glare, light intensity need and yellowing) and other senses (hearing, smell, taste and touch).

Immediate environment include geographical factors (climate, landscape and seasonal changes). Social factors (crowding, personal space and degree of awareness) and medical factors (survival and need, state of well-being and protection).

Our proposal „

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We shall only try to focus in what the human been us capable to see and process in his mind referred only to the scene he is evaluating without involving anything related to the mood or culture learnt in his life, or visual defects in his sight.

It is just try to understand how he process, in his brain, the picture he is looking up.

Appearance: something more than colour

It is composed by colour, cesia and spatiality.

Colour is composed by chroma and hue. Lightness or luminosity is shared with cesia.

Spatial colour is related to goniochromatism and, probably, to glints.

Visual appearance includes colour.

Cesia divides into permeability and diffusivity. The first includes opacity. Diffusion defines gloss and its contrary: diffuseness, also translucency and transparency.

The spatial cesia includes definition of image –DOI– , haze and clarity or cleanliness.

Spatiality is divided in two: One and two dimensions. The first includes waviness, orange peel, and granularity. Texture is bidimensional as also is coarseness.

Foods and its glossy appearance

Let us talk about gloss and light diffusion.

Normally if the object is illuminated by the sun or one lamp, light comes from one direction which is what produces gloss.

Also exists diffuse light coming from the sky or objects surrounding our glossy subject.

When direct light exists, if the object has a polished surface, gloss appears. As we have seen in the red apples. But also on surfaces with no polish, as strawberries or radish, produces some kind of gloss.

Foods and its translucency „

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Most fruits and juices are translucent.

But, What it means to be translucent?

That light traverses the product in different directions than the incident diffusing image as is seen in the picture

Gloss is related to goniophotometry.

What means that? „

Remember the Hunter`s gloss classification

Let us consider the measurement apertures and different type of gloss measurements

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Does not imply spatial distribution of the reflected light? And,.. Is it not a short draft of that distribution?

Let us see how the light is distributed around the specular component

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It is possible to see that the spatial distribution of light varies around the specular direction.

What is Goniophotometry..?

Foods have texture

Let us now talk about it „

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If gloss analysis is done through the measurement along space of one dimension, texture, at least, needs two.

How is this done? How people who works in animated cinema produce films like Monsters Inc., showing how shadows and sparks of their bodies changes while the protagonists are moving?

A completely new approach is marching on.

Then appeared spatial frequencies

Fourier Analysis „

Spatial frequencies can be analyzed through Fourier trigonometric series. Let as see the square function

It is possible to approach the function so much as wished

Let me show what it is new

This is the new form to measure spatial reflectance.

In Japan, Takagi, Sato and Baba measured 48139 points in the space over the sample (each 4º between 0º and 90º for the incident beam and each 2º from -90º to 90º for the reflected beam), taking 10 seconds for each measurement, working 8 hours daily, it took 16 days just one measurement. They could resume the data in 1485 measurements measured in 4 hours

What implies such amount of data?

The use of Fourier analysis and transform.

The study of the CSF –Contrast sensitivity Function– of the human visual system.

Also the MTF –Modulation Transfer Function–, applied to the human vision.

The compression and decode of the data through wavelets.

The appearance of textons and the statistic analysis of textures.

Arriving to an end

You may think that this presentation only complicate understanding of what we see usually.

Fruits, meat, bread…, etc., are what we see and recognize, no matter how complicated can be its description or its processing.

My problem is to understand how the human brain is processing the incredible number of signals simultaneously to codify which size, shape, colour and superficial appearance characterize the objects we see every moment.

If this is just to see colours… What do we need to see visual appearance?...

Most of you knows that to see colour we have three different detectors in our eyes.

Those detectors are connected to the brain through bipolar and ganglion cells by means of the optic nerve, which goes first to the chiasm, and the lateral geniculate nucleus and then to the visual cortex, where images are reproduced.

To see a texture is needed, at least, to discriminate 8 different spatial frequencies, and, also, 6 different angles respect to the vertical.

3 colours x 8 frequencies x 6 angles, that are

144 simultaneous variables.

144 different detectors!!! „

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This is what is, at least needed to see the visual appearance of the pictures we see any moment.

How this is achieved? Which are the detectors?

Which is the process?

This is my actual interrogant, which appeared while I was trying to re-write my old book on colour, and drive me to this amazing questioning on all matters related to the subject. Presently, I have no answer but I thought that this could be of interest to you.

Thank you for your kindness and patience