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Article # 6

Advanced Practice in Art 

Deconstructing Color Constancy and Value Perception – Part 3

The Problem of Color Constancy

In previous articles we discussed that the color of an object is comprised of both hue and value.  Therefore, when we discuss color illusions, value creeps back into the equation.  Because of this complexity, understanding the color defects in our recognition and finding ways to overcome them become more elusive.   I am convinced that the best way to address color illusions is to try to understand both components separately.  

In the last article we identified how value illusions manifest in our work: 

•  Highly saturated colors are painted too light or too dark.
•  Relatively dark areas within the light plane are painted too dark.
•  Relatively light areas within the shadow plane are painted too light.

I also provided two methods to overcome the value illusions:

•   I  demonstrated a split value palette exercise as a method to keep values within the correct light and shadow areas.  
•   I covered two ways to use black and white photographs to plan and check value assessment.  

In this article I will suggest two more methods, monochromatic underpainting and influenced color, to merge the value and color components.  But before I start that process a review of color constancy is essential.

Color Perception

The cones and rods in our eyes receive lightwaves.  The rods are better at discerning the shape and value of objects and are less adaptive to color.  The three types of cones (color receptors) are receptive to different spectrums of light that overlap.  As light entering the eye stimulates the cones and rods signals are sent to the brain where color and value are perceived differentially. 

Reflectance Ratios

Light is reflected from an object to the viewer in different proportions based on the amount of illumination.  Reflectance ratio is the objective ratio of this measured illumination.  The brain uses reflectance ratios to create color constancy and lightness constancy.

Color Constancy 

 Color constancy is the subjective perception by the brain that allows it to perceive the color of an object regardless of the degree or type of illumination of the object.  The ability of the brain to discern color under varying lighting conditions, such as in shadow or light, is a highly developed process that is essential for understanding our environment.  Color constancy strongly suggests that objects in light and shadow are the same color.  They are not.  Color constancy strongly suggest that objects under different illumination are the same color.  They are not.  In both situations objects are only perceived as the same color through the mechanism of reflectance ratios and color constancy.

In the following example we are presented with white aspen trees in light and shadow.   But are they really white?  The light reflected to the viewer is many different colors.  The trunks reflecting direct light are receiving the broadest spectrum of light and appear to be the whitest.  The shadow side of those same trunks reflect influences from the sky, grasses and foliage nearby.  This light is more of a warm gray color.  The trees in shadow reflect a very different light.  The lower part of the trunks reflect more cool blue light from the sky.  The upper part of these trunks have more warm green influences from the upper foliage.  The rods and cones in the eye merely transmit this information to the brain and then color and lightness constancy takes over.  The brain receives the reflectance data of color and value from the tree trunks and every other object in the scene.  It also takes into account the influences of each object on the other.  It concludes (perceives) that it is viewing white aspen trees in a green field.  The message to the artist is white tree - green field which is hard to overcome.  

When we experience illusions in the realm of color our recognition process consistently provides one answer:  The local color.  As artist we must move beyond the notion that any object is its local color because in nature objects rarely exist in isolation.  Reflected color is the norm.  We must, therefore, go back to the basics of different types of light and reflected color to arrive at the true color of an object:  The influenced color.  To paint nature convincingly we must use each object in a scene to describe other objects.  All of the elements work together to provide harmony and unity to the painting.  

Monochromatics

If we desire to isolate the two components of color, hue and value, the best way to start is to limit the color in our paintings at the beginning.   If we use one color to start a painting the confusion is reduced.  It engages the rods in our eyes and reduces the confusing information supplied by our cones.   We can concentrate on simplifying value shapes and masses in the design process.   

Stage 1 (Drawing stage):

I chose a resource photograph that I felt would be a good illustration of overcoming color constancy and value illusions.  From the beginning the challenge was to convincingly describe the white tree trunks with contrasting colors that represent the different sources of direct and reflected light.  I also saw this as a good example to illustrate value confusion presented by the dark background adjacent to the white tree trunks in shadow.  It was essential to place the tree trunks in shadow exactly in the proper color and value field if the painting was to succeed.

I began with a 24 in x 24 inch double primed gallery wrapped canvas.  I sketched the tree trunks and rough outlines of the foliage in with a 6h graphite pencil.  I emphasized margins of value masses rather than individual leaves.  I placed indicator marks on the trees at junctions of limbs, foliage and  where the dark areas began at the base of the trunks.  I purposefully skipped drawing every leaf and blade of grass to make the process more intuitive.  

When the drawing was completed I added two more thin coats of gesso to seal the graphite and to de-emphasize the drawing.  The drawing was barely noticeable after drying.  

Stage 2 (Monochromatic underpainting):

I painted from a high resolution monitor that displayed a full color and a desaturated version of the resource photograph side by side.  

The painting process started with a monochromatic block-in with Raw Umber.  I worked from the darkest dark areas towards the lighter areas in thin coats.  After the first coat dried I went over the darkest areas again to achieve the darkness I wanted and to prevent impasto areas within shadows.  

Stage 3 (Checking my work for value confusion) :

I desaturated a photograph of the painting and compared it to a black and white version of the resource photograph.  I paid special attention to the value relationships of the background and tree trunks in shadow.  Corrections were made at this point using Gamsol, paper towels, stiff bristle brushes and erasers.  Darker corrections were made with another layer of Raw Umber.

Finished monochromatic painting

Black and white resource photograph

Stage 4 (Color stage- Adding hue to value):

I chose a palette that included:

Titanium White

Ultramarine Blue

Alizarin Crimson

Transparent Red Oxide

Hookers Green

Yellow Green

Lemon Yellow

Raw Umber (underpainting)

Brushes:

Flats and filberts - Sizes 1-8, 

-Hobby quality for aggressive block in

- Rosemary and Co. Ivory for finish work

Since the greatest color and value confusion would occur when painting the background and the tree trunks I began there.  I laid in the background dark masses until the value approximated the underpainting value.  I chose a blue-grey color for the tree trunks in shadow as a summation of the colors reflecting into them.  Later I would repaint them with more influences such as warmer greens from the foliage in areas and bluer influences in areas with more exposure to the sky.  Careful attention was made to keep the values of these trunks in shadow darker than my mid grey toned palette (my breakpoint between light and shadow for this painting).

The tree trunks in the light plane were much more complex.  They consisted of areas in direct sunlight and areas in shadow.  The shadow side of these trees included warm reflected light from the trees next to them and areas of cooler light reflected from the sky.  I tried to maintain the shadow side of these tree trunks with mixtures that were darker than my palette even though they were screaming “white” to me.  At several points in this process I called a time out to evaluate the color. 

Did the value match the underpainting value?

Was the shadow color mixture darker than my palette?

Was the temperature relationship to the light side correct?

Was the temperature difference between these trunks and the trunks in deep shadow believable?  

Stage 5 (Painting the foliage and ground plane in light):

At this stage I was happy with the background and the tree trunks.  I began adding tree foliage from the back of the tree to the front and dark to light.  I looked for opportunities to mass values while turning form with temperature.  In between stages of the tree foliage I worked on the ground plane in the foreground and mid ground, trying to make the relationship between the grasses believable in temperature, form and value. 

Beginning the foliage from back to front and dark to light

Establishing the temperature and value relationships of the lighter foliage.

Establishing the temperature and value relationships of the ground plane in light to the grasses in shadow and the tree foliage.

Stage 6 (The finished painting)

Conclusion

Overcoming perception illusions requires practice and patience.  As a learning experience, a great amount of understanding can be gained from attempting and failing to express a concept.  If nothing else, we learn what not to do the next time.  But if we apply the principles behind the nature of the subject, a certain logic begins to unfold and we can circumvent the illusions.  The best method to achieve this is to paint from nature, fail, and then determine why we fail.  I hope these articles have provided some insights to why we sometimes fail at painting the correct color and values.  It is only then that we can make the corrections that lead to a more believable representation of nature.  

(Side note) - The ability of the artist to deconstruct color illusions and apply the logic of reflected light in his/her paintings greatly increases the ability to produce a likeness of nature through value massing and correct color.

  (Side Note)These principles are ever present in the natural world.  There, one will find a ready display of the interactions of color and light available for observation.  In addition to the general world around us we can also look to works of art for illustration of the principles.  I encourage the reader to examine the works of accomplished artists to see how they have applied these principles to achieve representation of light and color in practice.  You will find valuable information in their work, especially in the different perspectives of their application of the concepts.