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Who Am I ?
Ricardo SAPAICO
- PhD in Computer Science, Tokyo Institute of Technology
- 10+ years of expereicne
About DXO Labs
- ~18 years
- 50 people working in France
Products
- DxO PhotoLab
- LightRoom like
- DxO PureRaw
- Smaller version of PhotoLab
- Editing images quickly
- EISA award
- Nik Collection by DxO
- Plugin for Adobe
- DxO FilmPack
Back to the course
Why color matters ?
- Useful for quality inspection
- Rely on color for a small object
- Gives shape (shine color light on objects and create shadows)
- Cultural heritage
- Paintings
- If you take a picture of a painting, you want the photo to represents the painting well
- Same for printing a copy of the painting
- Printing
- Computer graphics
- Even tho not physical, you have to make sure you have the good colrs
- Photography
- Sometimes, it’s just a matter of doing the right thing to have a good picture
- From color to B&W is not easy
- Style Transfer IA on photography
- Hyperspectral images
Evaluation
- Attendance
- Each class attended, you get $+0.5$
- Writtent report
- Exercises using the data we will obtain during the TPs
- A litlle bit of investigation for solving a typical color-related probleme in cameras
- Group of 2 people
- Participation bonus: You can get up to $+2.0$ in your grade if:
- You ask me technical question by mail
- You ask technical questions in the IMCO group (Teams)
- You reply a technical question in the IMCO group (Teams)
Defining colors
White becomes pink with reflection
What is (not) color
- Color is NOT a property of an object
- Once in the dark, no more color
- Someone colorblind will see the color differently
- Color is NOT a particle
- Color is a sensation like touch
- Color is a sensation produced by a physical reality
Grass is NOT green and sky is NOT blue, They are perceived as green and blue They have physical properties that makes them look that way
Color is in your HEAD
How is color produced ?
- Sun: light
- Apple: object
- Human: sensor
Electromagnetic spectrum
How can you see the black if it doesn’t reflect any light ?
Because there is a shape (ex: a TV) Black isn’t a color but we can perceive it
If we have a white surface and a red beam of light coming in, it would reflect the red.
Object
Surface and subsurface interaction with light
- specular
- absorption
- diffuse
- transmittance
- refraction
- scattering
To know of colors will work on this textile, you can only know it by printing hundreds of colors and extrapolate for the other ones
Color is no ‘part’ of an object
- Dimension, shape, material (what it’s made of), volume, density, porosity
Sensor
Human vision system
Reminder Refractive index:
\[n=\frac{c}{\nu}\]
- Cornea
- The most significant image-forming element of the eye
- Eye problemes, such as nearsightedness, farsightedness, astigmastism, can be attributed to it
- Lens
- Serves the function of accomodation
- It is layered, flexible structure that varies in index of refraction. This feature serves to reduce some of the aberrations
- Distant object: it becomes “flatter” resulting in the decreased optical power
- Nearby object: it becomes “fatter” thus has increased power
- As we age, we lose flexibility. When we are about 50 years, the lens has completely lost its flexibility
- Iris + pupil
- controls the pupil size
- Pupil is the hole in the middle of the iris through which light passes. The pupil size is largely determined by the overall level of illumination
- Pigmentation in the iris is what gives us color
- Retina
- A thin layer of cells, approximately the thickness of tissue paper
- Contains the visual system’s photosensitive cells + initial signal processing and transmission “circuitry”
- Photoreceptios: Rods and Cones
- Fovea
- Area on the retina where we have the best spatial and color vision
- Optical nerve
- Transfer info from the retina to the brain
- 1 million fibers vs 130 million photoreceptors
- There is a compression of the visual system
- There are no photoreceptors where the nerve is
- blind spot
Rods and cones
Cones: useful to perceive color Rods: useful in low-light
3 types of cones:
- Long
- Medium
- Short
Fun fact Most mammals have only blue and green cones, only primates have red
Color matching experiment
The observer adjusts the intensity of the primary colors until the results matches the test This test was like 100 years ago
Chromaticity diagram
Spectrum Locus Chromaticity of monochromatic light at specified wavelength
Spatial properties of Color Vision
In JPEG we have an image divided in luminance and chromatic information. Our eyes are less sensitive to chromatic infos, so JPEG subsamples then reconstructs the image
How to (re)produce color ?
- Additive process (RGB)
- Light mixing
- Substractive process (CMY)
- Used in printing
- Paint mixing
Color framework
Bonus
Facts about animals
- Most fish, frogs and turtle and 3 to 5 cones
- Most mammals have retinas where rods predominate
- Is it because the Earth was dark when first mammals appeared ?
- Nocturnal mammals like rats and mice have retinas dominated by rods (only 3 to 5% of cones)
- Snakes can see ultraviolet light
Why the eyes reflect the light ?
In the eyes, there are epithelial cells
Epithelial cells Prevents light from going back to the retina $\to$ keeps the sharpness and contrast
Nocturnal animals exchange image quality for image power. Their cells reflects the light back $\to$ the photoreceptors have a second chance to absorb energy
Different than having red eyes !
Structural color: Iridiscence
Used for camouflage
Facts about humans
- Red-green color blindness
- $8\%$ males (XY chromosome)
- $0.5\%$ females (XX chromosome)
of northern European descent
Around $12\%$ of the female population could be tetrachromatic
To think over
- What is fluorescence ?
- Why a banana stays yellow under 2 different light sources ?