## 1. Introduction

We are going to analyse some features of screens.

## 2. Screen analysis.

 For the questions below, you’ll answer on this document: response document

Look at the picture of an Iphone

1. What can you see ? Give the definition of a pixel (you can find this information on the web)

Open the file « couleurs_ecran.swf » SWFOpener software.

Observe how adjusting the intensity of the 3 red, green and blue sub-pixels can generate a multitude of colors.

2. How many different colors can be generated knowing that each sub-pixel (red, green or blue) has 256 possible shades?

 By using the following site https://www.w3schools.com/colors/colors_rgb.asp or with the paint color chart ( see below):

Answer the questions *on your own document* and check the responses with this questionnaire below.

1. What are the settings of RGB values to get the white color?:
1. rgb(253, 253, 253)
2. rgb(255, 255, 255)
3. rgb(03, 0, 0)

2. What are the settings of RGB values to get the color black?
1. rgb(255, 255, 255)
2. rgb(03, 0, 0)
3. rgb(0, 0, 0)

3. What are the settings of RGB values to get the gray color?
1. rgb(128,128,128)
2. rgb(192,192,192)
3. rgb(220,220,220)

4. What are the settings of RGB values to get the pink color?
1. rgb(255, 0, 255)
2. rgb(128, 0, 255)
3. rgb(0, 128, 255)

5. What are the settings of RGB values to get the yellow color?
1. rgb(255, 0, 255)
2. rgb(128, 0, 255)
3. rgb(255, 255, 0)

## 3. Repartition of pixels on a screen.

When observing screens, we can see differences in the arrangement or shape of pixels (and sub-pixels), depending on the model of Smartphone observed.

1. Castagnetto, académie de Strasbourg image::images/pixel.png[align="center"]

There are two important concepts to Know (very often confused): definition and resolution

• The definition of a screen is the number of pixels that make up the screen. Please note, we are not talking about the red, green, blue sub-pixels here, but the global pixel created by the combination of these three sub-pixels. This definition is for example given in the form 1920x1080.

• Resolution of a screen: it is generally expressed in dpi (dots per inch) or ppi (pixels per inch) or ppp (pixels per inch in french): It measures the number of available pixels over a length of 1 inch (approximately 2, 54 cm). Higher is the number, smaller the pixel size is, and more precise the image will appear.

 Le format des écrans est un ratio (par exemple 4/3 ou encore 16/9) qui représente le rapport entre la largeur et la hauteur de l’écran: si l’écran a pour dimensions 548mm (largeur) x 308mm (hauteur). Le format est alors de 548 / 308 = 16/9. Les formats les plus utilisés sont le 16/9 puis le 16/10, suivit de l’ancien 4/3 (en général pour les écrans cathodiques). Voici une image de comparaison du 16/9 avec le 4/3:
`CONTINU TO RESPOND ON YOUR OWN DOCUMENT.`
1. The terms "HD", "Full HD" and "4K" are standards for screen definitions. Find the values of these definitions.

2. Determine the definition of your phone screen. You can find this information in the specifications of your phone.

3. Measure the width of your phone screen, and convert this measurement to inches.

4. Calculate the resolution of your screen (expressed in pixels per inch). You can compare your calculation with the information found in your phone specifications. You can also check your calculations through the site http://www.pxcalc.com/.

### 3.1. Practice.

a 4K TV with these spécifications:

Knowing that the screen format is 16/9 and that the screen size is 55 inches (the length of its diagonal)

1. Calculate the width and height of the screen in inches.( you can use the Pythagorean Theorem)

2. Calculate the resolution of this TV screen in dpi.

3. Compare with the resolution of your phone screen calculated before.

## 4. Listenning comprehension.

Watch this video:

## 5. Workshop

by group of 3 pupils at most, you’ll prepare a short oral presentation with some slides.

The slide show will give information about:

1. the technical characteristics of the screen. specially the calculations about definition and resolution.