1. Electronics Lecture 1 by Dr. Mona Elneklawi

2. Color in the eye
The ability of the human eye to distinguish colors is based upon the varying sensitivity of different cells in the retina to light of different wavelengths. Humans being trichromatic, the retina contains three types of color receptor cells, or cones. One type, relatively distinct from the other two, is most responsive to light that is perceived as blue or blue-violet, with wavelengths around 450 nm; cones of this type are sometimes called short-wavelength cones, S cones, or blue cones

3. . The other two types are closely related genetically and chemically: middle-wavelength cones, M cones, or green cones are most sensitive to light perceived as green, with wavelengths around 540 nm, while the long-wavelength cones, L cones, or red cones, are most sensitive to light is perceived as greenish yellow, with wavelengths around 570  nm.

4. RGB (red, green, and blue)
RGB (red, green, and blue) refers to a system for representing the colors to be used on a computer display. Red, green, and blue can be combined in various proportions to obtain any color in the visible spectrum. Levels of R, G, and B can each range from 0 to 100 percent of full intensity. Each level is represented by the range of decimal numbers from 0 to 255 (256 levels for each color), equivalent to the range of binary numbers from to , or hexadecimal 00 to FF. The total number of available colors is 256 x 256 x 256, or 16,777,216 possible colors.

5. A bit (short for binary digit) is the smallest unit of data in a computer. A bit has a single binary value, either 0 or 1.
Pixel in digital imaging, a pixel, pel, dots, or picture element is a physical point in a raster image, or the smallest addressable element in an all points addressable display device; so it is the smallest controllable element of a picture represented on the screen.

6. Monochrome palette means a set of intensities for a monochrome display, and the term RGB palette is defined as the complete set of combinations a given RGB display can offer by mixing all the possible intensities of the red, green, and blue primaries available in its hardware.

7. Floyd Steinber dithering
Bits
Monochrome (1-bit) black and white
2-bit grayscale 22 = 4 levels of gray
4-bit grayscale 24 = 16 levels of gray
8-bit grayscale 28 = 256 levels of gray
No dithering
Floyd Steinber dithering
Gradient

8. Additive coloring
Additive color is light created by mixing together light of two or more different colors. Red, green, and blue are the additive primary colors normally used in additive color systems such as projectors and computer terminals. Additive color mixing: combining red and green yields yellow; combining all three primary colors together yields white.

9. Subtractive coloring
Subtractive color mixing: combining yellow and magenta yields red; combining all three primary colors together yields black.
Subtractive coloring uses dyes, inks, pigments, or filters to absorb some wavelengths of light and not others. The color that a surface displays comes from the parts of the visible spectrum that are not absorbed and therefore remain visible. Without pigments or dye, fabric fibers, paint base and paper are usually made of particles that scatter white light (all colors) well in all directions. When a pigment or ink is added, wavelengths are absorbed or "subtracted" from white light, so light of another color reaches the eye.

10. Each permuted pair of red, green, and blue
Dichrome palettes
Each permuted pair of red, green, and blue
16-bit Red Green
16-bit Red Blue
16-bit Green Blue
Additive
Subtractive

11. Regular RGB palettes
These full RGB palettes employ the same number of bits to store the relative intensity for the red, green and blue components of every image's pixel color. Thus, they have the same number of levels per channel and the total number of possible colors is always the cube of a power of two. It should be understood that 'when developed' many of these formats were directly related to the size of some host computers 'natural word length' in bytes—the amount of memory in bits held by a single memory address such that the CPU can grab or put it in one operation.

13. Non-regular RGB palettes
These are also RGB palettes, in the sense defined above (except for the 4-bit RGBI, which has an intensity bit that affects all channels at once), but either they do not have the same number of levels for each primary channel, or the numbers are not powers of two, so are not represented as separate bit fields. All of these have been used in popular personal computers

15. RGB arrangements
These are selections of colors based on evenly ordered RGB levels, mainly used as master palettes to display any kind of image within the limitations of the 8-bit pixel depth.

17. Other common uses of software palettes

18. Character color
The consensus is that the "non-colors", white and black, and the colors yellow, green, and orange are generally most acceptable. These colors (yellow, green, orange) are in the middle of the visible spectrum (the range of colors that our eyes can detect) and are the easiest for the eye to see. Our eyes are not as receptive or sensitive to the colors at the extreme ends of the visible spectrum (e.g., blue, violet/purple, and red). The focus point inside the eye for different colors is situated at different distances behind the lens. To simultaneously see different colors well, the eye has to focus quickly and alternatively at different distances

19. . The further the colors are from each other in the visible spectrum, the more difficult the process is. When we try to focus at the same time on colors situated at opposite ends of the spectrum (e.g., red and blue), our eyes get more tired than when we focus on colors which are close to one another in the spectrum (e.g. green and yellow). Characters in colors situated at the extreme ends of the visible spectrum should probably be avoided unless displayed on a light or contrasting background.

20. Display polarity
Positive polarity means that a monitor displays dark characters on a light background, while negative polarity means that light characters are displayed on a dark background. One polarity has little advantage over the other. The resolution of positive polarity screens tends to be less affected by glare (screen reflections). Also, the dark characters on a light background are similar to what we are most used to in print materials. On the other hand, it tends to make screen flicker more noticeable. Given the same luminance (intensity of the light from the screen), negative polarity provides better character contrast and is less prone to flicker. User preference should be the determining factor when setting display polarity.

21. Image contrast and resolution
The image contrast is given by the ratio between the brightness of the "white" and the brightness of the "black" the monitor can reproduce. A higher contrast of the display can give the impression of increased brightness and can increase the capacity of noticing details.
There are two types of contrast ratio: "static" contrast ratio and "dynamic" contrast ratio.

22. The "static" contrast ratio is the contrast ratio that can be produced at any moment in time, and is determined by calculating the ratio between the brightness of "white" and the brightness of "black" within a single picture on a display situated in a complete dark room.

23. The "dynamic" contrast ratio compares the brightest whites and the darkest blacks from different scenes of a movie. The display equipped with dynamic contrast ratio (DCR) has the ability to make dark scenes even darker by adjusting the intensity of the backlight. In this way, the ratio between the luminosity of the whitest white among all images and the darkest black from all images increases. As a consequence, the dynamic contrast ratio is always much higher than the static contrast ratio.
The monitors used in offices do not usually have DCR technology, so they are characterized by the "static contrast ratio".

24. Fairly sharp images and adequate contrast ratios are typically required to make a display easier to read.
The human eye can perceive changes in contrast up to about 1000:1 ratio. Changes are more noticeable when we pass from 10:1 contrast ratio to a 20:1 contrast ratio. As the contrast ratio increases the difference is noticed less. For example, the difference in contrast at ratios higher than 500:1 up to 1000:1 will seem minor. The contrast perceived by the viewer will be always less than the given contrast ratio for the monitor. This difference is due to the fact that the monitors are usually in an office setting where the reflection of the surrounding light will reduce the contrast.
What is acceptable to an individual will also depend on character size, viewing distance and the type of task being done. A properly functioning monitor will typically provide adequate resolution and a static contrast ratio up to 1000:1.