Unit 1 The History of Photography & The Camera

Digital Capture

Introduction Digital photographs are made up of millions of tiny squares called picture elements = pixels. The computer divides the screen or printed page into a grid of pixels. It then uses the values stored in the digital photograph to specify the brightness and colour of each pixel in this grid.

See how dots make up an image’s resolution. High Resolution is 300 dpi at the size you want to print Low Resolution is 72 dpi at the size you want to print See how dots make up an image’s resolution.

Number of Pixels The quality of a digital image depends on the number of pixels used to create the image = resolution. The more pixels = more detail. There are ALWAYS size limitations. Higher ISO will give more pixelation – due to (FILM GRAIN-larger crystals)

The Size of a Photograph Two measurements By its dimensions in pixels 3888x2592 pixels By the total number of pixels it contains 3888x2592 = 10.1 million pixels or megapixels

How an Image is Captured The big difference between traditional film cameras and digital cameras is HOW they capture the image. Instead of film digital cameras have a solid-state device called an image sensor. On the surface of the finger-nail sized silicon chip is a grid containing over 10 million photosensitive diodes called photosites, photoelements or pixels. Each photosite captures a single pixel in the photograph to be. See why a sensor is called a Charged Coupled Device.

The Exposure When you press the shutter button an exposure system measures the light coming through the lens and sets the aperture an shutter speed for the correct exposure. When the shutter opens briefly, each pixel on the image sensor records the brightness of the light that falls on it by accumulating an electrical charge. The more light that hits a pixel, the higher charge it records. Pixels capturing light from shadows will have low charges. When the shutter closes to end the exposure, the charge from each pixel is measured and converted into a digital number. This series of numbers is then used to reconstruct the image by setting the colour and brightness of the matching pixels on the screen or printed page.

It’s all Black and White An image sensor can only capture brightness, not colour. They record only the gray scale – a series of 256 increasingly darker tones ranging from pure white to pure black.

How Colour is Captured James Clerk Maxwell in 1860 that discovered that colour photographs could be created using black and white film and red, blue, and green filters. Thomas Sutton photographed the same photograph (a tartan ribbon) three times, each time with a different filter over the lens. The three black and white images were then projected onto a screen with three different projectors, each equipped with the same colour filter used to take the image being projected. When the three images are brought into alignment, the three images formed a full-colour photograph.

How Colour is Captured … Colours in a photo are based on the three primary colours, red, green, blue (RGB). This is called the additive colour system because when all three colours are combined in equal amounts = white. This RGB system is used whenever light is projected to form colours (monitor, tv, projector) Since daylight is made up of RGB, placing red, green and blue filters over individual pixels on the image sensor can create colour images just as they did for Maxwell in 1860. See how the additive colour theory create colour images.

Image Formats JPEG RAW Joint Photographers Expert Group Default image type in cameras Compress FINE – less compression = larger prints RAW Better than jpeg (quality) but not post-processed Captures EVERY BIT of the captured data, unlike jpeg which are processed in the camera with some data being discarded (compression). See the difference between JPEG and RAW images.

Image Quality