The Quality Factors of Digital Photograph

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The Digital Photograph

Computers are amazing machines. Their strength is in being able to perform millions of mathematical calculations per second. To apply this ability to working with images, we must start with a description of pictures that the computer can understand.

This means that the images must be in a digital form. This is quite different from the way our eye, or any film-based camera, sees the world. With film, for example, we record pictures as a series of ‘continuous tones’ that blend seamlessly with each other. To make a version of the image that the computer can use, these tones need to be converted to a digital form.

The process involves sampling the image at regular intervals and assigning a specific color and brightness to each sample. In this way, a grid of colors and tones is created which, when viewed from a distance, will appear like the original image or scene. Each individual grid section is called a picture element, or pixel.

There are several post production processing for digital photography, such as Clipping Path, Photo Retouching, Photo Manipulation, Image Masking, Color Correction, Vector Conversion and Ghost Mannequin etc. We will discuss all about this photo editing services in our upcoming blogs.

Creating Digital Photos

Digital files can be created by taking pictures with a digital camera or by using a scanner to convert existing prints or negatives into pixel form. Most digital cameras have a grid of sensors, called charge-coupled devices (CCDs), in the place where traditional cameras would have film. Each sensor measures the brightness and color of the light that hits it. When the values from all sensors are collected and collated, a digital picture results.

Scanners work in a similar way, except that these devices use rows of CCD sensors that move slowly over the original, sampling the picture as they go. Generally, different scanners are needed for converting film and print originals; however, some companies are now making products that can be used for both.

Digital Photograph is made up of pixels.
A digital picture is made up of a grid of picture elements or pixels.

Video cameras use the same principle but rapidly capture a sequence of images. Any movement in the subject is recorded on successive photos. When these images, or frames, are quickly re-displayed one after another, the motion of the subject is replicated on screen. Until recently, capturing digital video required a separate camera, now, many still cameras also contain a very usable video mode.

Photo Conversion
Photographs and negatives, or slides, are converted to digital pictures using either film or flatbed scanners.

Quality Factors in a Digital Image

The quality of the digital file is largely determined by two factors – the number of pixels and the number and accuracy of the colors that make up the image. The number of pixels in a picture is represented in two ways – the dimensions, i.e. ‘the image is 900 × 1200 pixels’, or the total pixels contained in the image, i.e. ‘it is a 3.4 megapixel picture’.
Generally, a file with a large number of pixels will produce a better quality image overall and provide the basis for making larger prints than a picture that contains few pixels. The second quality consideration is the total number of colors that can be recorded in the file. This value is usually referred to as the ‘color or bit depth’ of the image.

Size of Digital Image
The size of a digital image is measured in pixels. Images with large pixel dimensions are capable of producing big prints and are generally better quality.

The current standard is known as 24-bit color or 8 bits per Red, Green and Blue channel. A picture with this depth is made up of a selection of a possible 16.7 million colors. In practice this is the minimum number of colors needed for an image to appear photographic. In the early years of digital imaging, 256 colors (8 bits of color per channel) were considered the standard.

Although good for the time, the color quality of this type of image is generally unacceptable nowadays. In fact, new camera and scanner models are now capable of 12 bits per channel (36-bit color altogether) or even 16 bits per channel (48-bit color altogether). This larger bit depth helps to ensure greater color and tonal accuracy.

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