Pixels, Resolution and Pixel Value
For a machine to see a picture, the picture has to be numbers. This lesson is about what those numbers are. Three of the four terms here have been one-mark board questions.
1Pixel
The more pixels you have, the more closely the image resembles the original. Magnify any photograph far enough and the squares appear.
Every photograph in digital form is made of pixels. Drag sideways to turn the grid and look along it.
A pixel is a picture element: the smallest unit of information that makes up a picture, arranged in a 2-dimensional grid.
2Resolution
The other convention gives a single number: a 5 megapixel camera, where a megapixel is a million pixels. That means width × height comes to 5 million. Our 1280×1024 monitor is 1280 × 1024 = 1,310,720, or about 1.31 megapixels.
Tiles on a wall
3Pixel value
4Why 255?
Computer data is stored in the binary system: every bit is a zero or a one. Each pixel uses 1 byte, which is 8 bits. Each bit has two possible values, so eight bits together give:
Those 256 values start at 0 and end at 255. There are 256 of them; the largest is 255. That is why the range is 0–255 and not 1–256.
Tap any square in the grid. Every one of these 256 pixels is three numbers, and nothing else.
| row, column | 4, 12 |
| R | 255 |
| G | 214 |
| B | 64 |
| as grayscale | 209 |
This image is 16 × 16, so it holds 256 pixels and 768 numbersin total — three per pixel. Every value sits between 0 and 255.
5From the board papers
(A) 0 to 100 (B) 0 to 255 (C) 1 to 256 (D) −128 to 127CBSE board exam 2026
▶Show the answer
(B) 0 to 255. Option (C) is the trap: there are indeed 256 values, but they run from 0, so the last one is 255.
(A) More pixels result in lower image quality. (B) Pixels and resolution are unrelated concepts. (C) Resolution depends only on image file size. (D) The number of pixels in an image is known as resolution.CBSE board exam 2026
▶Show the answer
(D) The number of pixels in an image is known as resolution. That is the definition. (A) is backwards — more pixels means higher quality.
(a) Pixel Depth (b) Resolution (c) Colour Depth (d) ClassificationCBSE sample paper 2025–26
▶Show the answer
(b) Resolution. Width by height is the standard way of writing it.
▶Show the answer
A byte image is the most common pixel format, in which each pixel value is stored as an 8-bit integer — one byte. That gives 2⁸ = 256 possible values, so the range of pixel values runs from 0 to 255, where 0 is black or no colour and 255 is white or full colour.
▶Show the answer
Resolution is the number of pixels in an image, usually written as the width by the height.
For example, a monitor resolution of 1280×1024 means there are 1280 pixels from one side to the other and 1024 from top to bottom. It can also be given as a single number — 1280 × 1024 = 1,310,720, or about 1.31 megapixels.
6Check yourself
What does the word 'pixel' mean?
What does a pixel value represent?
Why does a byte image have 256 possible values?
How is resolution typically expressed?