Implementation of edge detection for a digital image

2.3.1. DIGITAL CAMERAS

2.3.1.0. DEFINITION OF DIGITAL CAMERA.

A digital camera is an electronic device used to capture and store photographs digitally, instead of using photographic film like conventional cameras, or recording images in an analog format to magnetic tape like many video cameras. Modern compact digital cameras are typically multifunctional, with some devices capable of recording sound and/or video as well as photographs.

2.3.1.1. CLASSIFICATION OF DIGITAL CAMERAS

Digital cameras can be classified into several categories:

· Video cameras

· live preview digital cameras

· Digital single lens reflex cameras

· Digital range finders

· Professional modular digital cameras systems

· Line scan cameras system

VIDEO CAMERAS

Video cameras are classified as devices whose main purpose is to record moving images.

Professional video cameras such as those used in television and movie production. These typically have multiple image sensors (one per color) to enhance resolution and color gamut. Professional video cameras usually do not have a built-in VCR or microphone

They generally include a microphone to record sound, and feature a small liquid crystal display to watch the video during taping and playback.

LIVE PREVIEW DIGITAL CAMERAS

In addition, many Live-Preview Digital cameras have a "movie" mode, in which images are continuously acquired at a frame rate sufficient for video.

Main article: Live-preview digital camera

The term digital still camera (DSC) most commonly refers to the class of live-preview digital cameras, cameras that use an electronic screen as the principal means of framing and previewing before taking the photograph. All use either a charge-coupled device (CCD) or a CMOS image sensor to sense the light intensities across the focal plane.

Many modern live-preview cameras have a movie mode, and a growing number of camcorders can take still photographs.

DIGITAL SINGLE LENS REFLEX CAMERAS

Digital single-lens reflex cameras (DSLRs) are digital cameras based on film single-lens reflex cameras (SLRs), both types are characterized by the existence of a mirror and reflex system. See the main article on DSLRs for a detailed treatment of this category.

DIGITAL RANGE FINDERS

A rangefinder is a focusing mechanism once widely used on film cameras, but much less common in digital cameras. The term rangefinder alone is often used to mean a rangefinder camera, that is, a camera equipped with a rangefinder

PROFESSIONAL MODOLAR DIGITAL CAMERA SYSTEMS

This category includes very high end professional equipment that can be assembled from modular components (winders, grips, lenses, etc.) to suit particular purposes. Common makes include Hasselblad and Mamiya. They were developed for medium or large format film sizes, as these captured greater detail and could be enlarged more than 35mm.

Typically these cameras are used in studios for commercial production

LINE SCAN CAMERAS SYSTEM

A line-scan camera is a camera device containing a line-scan image sensor chip, and a focusing mechanism. These cameras are almost solely used in industrial settings to capture an image of a constant stream of moving material. Unlike video cameras, line-scan cameras use a single array of pixel sensors, instead of a matrix of them. Data coming from the line-scan camera has a frequency, where the camera scans a line, waits, and repeats. The data coming from the line-scan camera is commonly processed by a computer, to collect the one-dimensional line data and to create a two-dimensional image. The collected two-dimensional image data is then processed by image-processing methods for industrial purposes.

2.3.1.2. IMAGE RESOLUTION

The resolution of a digital camera is often limited by the camera sensor (usually a charge-coupled device or CCD chip) that turns light into discrete signals, replacing the job of film in traditional photography. The sensor is made up of millions of "buckets" that collect charge in response to light. Generally, these buckets respond to only a narrow range of light wavelengths, due to a color filter over each. Each one of these buckets is called a pixel, and a demosaicing/interpolation algorithm is needed to turn the image with only one wavelength range per pixel into an RGB image where each pixel is three numbers to represent a complete color.

The one attribute most commonly compared on cameras is the pixel count. Due to the ever increasing sizes of sensors, the pixel count is into the millions, and using the SI prefix of mega- (which means 1 million) the pixel counts are given in megapixels. For example, an 8.0 megapixel camera has 8.0 million pixels.

The pixel count alone is commonly presumed to indicate the resolution of a camera, but this is a misconception. There are several other factors that impact a sensor's resolution. Some of these factors include sensor size, lens quality, and the organization of the pixels (for example, a monochrome camera without a Bayer filter mosaic has a higher resolution than a typical color camera). Many digital compact cameras are criticized for having excessive pixels, in that the sensors can be so small that the resolution of the sensor is greater than the lens could possibly deliver.

2.3.1.3. METHODS OF IMAGES CAPTURE

This digital camera is partly disassembled. The lens assembly (bottom right) is removed, but the sensor (top right) still captures a usable image, as seen on the LCD screen (bottom left).

Since the first digital backs were introduced, there have been three main methods of capturing the image, each based on the hardware configuration of the sensor and color filters.

The first method is often called single-shot, in reference to the number of times the camera's sensor is exposed to the light passing through the camera lens. Single-shot capture systems use either one CCD with a Bayer filter mosaic it, or three separate image sensors (one each for the primary additive colors red, green, and blue) which are exposed to the same image via a beam splitter.

The second method is referred to as multi-shot because the sensor is exposed to the image in a sequence of three or more openings of the lens aperture. There are several methods of application of the multi-shot technique. The most common originally was to use a single image sensor with three filters (once again red, green and blue) passed in front of the sensor in sequence to obtain the additive color information. Another multiple shot method utilized a single CCD with a Bayer filter but actually moved the physical location of the sensor chip on the focus plane of the lens to "stitch" together a higher resolution image than the CCD would allow otherwise. A third version combined the two methods without a Bayer filter on the chip.

The third method is called scanning because the sensor moves across the focal plane much like the sensor of a desktop scanner. Their linear or tri-linear sensors utilize only a single line of photosensors, or three lines for the three colors. In some cases, scanning is accomplished by rotating the whole camera; a digital rotating line camera offers images of very high total resolution.

The choice of method for a given capture is of course determined largely by the subject matter. It is usually inappropriate to attempt to capture a subject that moves with anything but a single-shot system. However, the higher color fidelity and larger file sizes and resolutions available with multi-shot and scanning backs make them attractive for commercial photographers working with stationary subjects and large-format photographs. CMOS-based single shot cameras are also somewhat common.[5]

2.3.1.4. IMAGE FILE FORMATS.

Common formats for digital camera images are the Joint Photography Experts Group standard ( JPEG) and Tagged Image File Format ( TIFF).

They usually store images in one of two formats TIFF, which is uncompressed, and JPEG, which is compressed. Most cameras use the JPEG file format for storing pictures, and they sometimes offer quality settings (such as medium or high).

JPEG is a compression algorithm developed by people the format is named after, the Joint Photographic Experts Group.

JPEG is big selling point is that its compression factor stores the image on the hard drive in less bytes than the image is when it actually displays.

JPEG uses lossy compression (lossy meaning "with losses to quality"). Lossy means that some image quality is lost when the JPG data is compressed and saved, and this quality can never be recovered.

TIFF - Tag Image File Format

TIFF is the format of choice for archiving important images. TIFF is THE leading commercial and professional image standard. TIFF is the most universal and most widely supported format across all platforms, Mac, Windows, Unix. Data up to 48 bits is supported.

TIFF image files optionally use LZW lossless compression. Lossless means there is no quality loss due to compression. Lossless guarantees that you can always read back exactly what you thought you saved, bit-for-bit identical, without data corruption. This is a critical factor for archiving master copies of important images. Most image compression formats are lossless, with JPG and PCD files being the main exceptions

Graphic Interchange Format (GIF)

GIF was developed by CompuServe to show images online (in 1987 for 8 bit video boards, before JPG and 24 bit color was in use). GIF uses indexed color, which is limited to a palette of only 256 colors (next page). GIF was a great match for the old 8 bit 256 color video boards, but is inappropriate for today's 24 bit photo images.

PNG - Portable Network Graphics

PNG is not so popular yet, but it's appeal is growing as people discover what it can do. PNG was designed recently, with the experience advantage of knowing all that went before. The original purpose of PNG was to be a royalty-free GIF and LZW replacement. However PNG supports a large set of technical features. Compression in PNG is called the ZIP method.

2.3.1.5 IMAGE CAPTURING

A light source say a candle emits light in all directions. The rays of light all start at the same point the candle's flame and then are constantly diverging. A converging lens takes those rays and redirects them so they are all converging back to one point. At the point where the rays converge, you get a real image of the candle.

2.3.1.6 DIFFERENCE BETWEEN FILM CAMERAS AND DIGITAL CAMERAS

The digital camera is one of the most remarkable instances of this shift because it is so truly different from its predecessor. Conventional cameras depend entirely on chemical and mechanical processes you don't even need electricity to operate them. On the other hand, all digital cameras have a built-in computer, and all of them record images electronically.

The new approach has been enormously successful. Since film still provides better picture quality, digital cameras have not completely replaced conventional cameras. But, as digital imaging technology has improved, digital cameras have rapidly become more popular.