Management of large sets of image data Capture, Databases, Image Processing, Storage, Visualization Karol Kozak Download free books at Karol Kozak Management of large sets of image data Capture, Databases, Image Processing, Storage, Visualization 2 Management of large sets of image data: Capture, Databases, Image Processing, Storage, Visualization 1st edition © 2014 Karol Kozak & bookboon.com ISBN 978-87-403-0726-9 3 Management of large sets of image data Contents Contents 1 Digital image 6 2 History of digital imaging 10 3 Amount of produced images – is it danger? 18 4 Digital image and privacy 20 5 Digital cameras 27 5.1 Methods of image capture 31 6 Image formats 33 7 Image Metadata – data about data 39 8 Interactive visualization (IV) 44 9 Basic of image processing 49 4 Management of large sets of image data Contents 10 Image Processing software 62 11 Image management and image databases 79 12 Operating system (os) and images 97 13 Graphics processing unit (GPU) 100 14 Storage and archive 101 15 Images in different disciplines 109 15.1 Microscopy 109 15.2 Medical imaging 114 15.3 Astronomical images 117 15.4 Industrial imaging 118 16 Selection of best digital images 120 References: 124 5 Management of large sets of image data Digital image 1 Digital image A digital image is a numeric representation (normally binary) of a two-dimensional image. Depending on whether the image resolution is fixed, it may be of vector or raster type. By itself, the term “digital image” usually refers to raster images or bitmapped images. Digital images may be produced in black and white (bitonal), grayscale, or color. Digital images are composed of very small picture elements – called pixels – lined up in rows and columns. Because pixels are the smallest picture elements, the pixel size determines how much detail will appear in the image: the smaller the pixels, the more pixels can appear in a given area, which results in higher resolution. Pixels are bundles of digital information about the color of a specific spot in the image. Basic image parameters are: pixel per inch, dots per inch, type of image (black & white, color), resolution, image depth, brightness, dynamic range, contrast, saturation, sharpness, image size, artifact. Pixels per inch (PPI) A digital image is composed of samples that the screen displays in pixels. The PPI is display resolution. How an image looks on screen is determined by the resolution of the monitor. Dots per inch (DPI) DPI is a measure of the resolution of a printer referring to how many dots of ink or toner a printer can place within an inch (or centimeter). DPI is printer resolution. Figure 1. Each pixel has a value from 0 (black) to 255 (white). The possible range of the pixel values depend on the colour depth of the image, here 8 bit = 256 tones or greyscales (source image [55]). 6 Management of large sets of image data Digital image Black and white images A black and white image is made up of pixels each of which holds a single number corresponding to the gray level of the image at a particular location. These gray levels span the full range from black to white in a series of very fine steps, normally 256 different grays. Since the eye can barely distinguish about 200 different gray levels, this is enough to give the illusion of a stepless tonal scale as illustrated below: Assuming 256 gray levels, each black and white pixel can be stored in a single byte (8 bits) of memory (Fig. 1). Color image A color image is made up of pixels each of which holds three numbers corresponding to the red, green, and blue levels of the image at a particular location. Red, green, and blue (sometimes referred to as RGB) are the primary colors for mixing light – these so-called additive primary colors are different from the subtractive primary colors used for mixing paints (cyan, magenta, and yellow). Any color can be created by mixing the correct amounts of red, green, and blue light. Assuming 256 levels for each primary, each color pixel can be stored in three bytes (24 bits) of memory. This corresponds to roughly 16.7 million different possible colors. Resolution The more points at which we sample the image by measuring its color, the more detail we can capture. The density of pixels in an image is referred to as its resolution. The higher the resolution, the more information the image contains. If we keep the image size the same and increase the resolution, the image gets sharper and more detailed. Alternatively, with a higher resolution image, we can produce a larger image with the same amount of detail. Image depth Call also BIT DEPTH is determined by the number of bits used to define each pixel. The greater the bit depth, the greater the number of tones (grayscale or color) that can be represented. - A pixel with a Image depth of 1 has two possible values: black or white - A pixel with a Image depth of 8 has 28, or 256 possible values - A pixel with a Image depth of 24 has 224, or approx. 17 million possible values A bitonal image is represented by pixels consisting of 1 bit each, which can represent two tones (typically black and white), using the values 0 for black and 1 for white or vice versa. 7 Management of large sets of image data Digital image A grayscale image is composed of pixels represented by multiple bits of information, typically ranging from 2 to 8 bits or more. A greyscale (i.e. monochrome / black & white) image uses one ‘byte’ per pixel (a ‘byte’ being 8 ‘bits’). An 8 bit unit or a ‘byte’, as it is called, can store up to 256 levels of information. In this way we can store up to 256 levels of brightness per pixel – which gives us an ‘8 bit greyscale’. A color image is typically represented by a bit depth ranging from 8 to 24 or higher. With a 24-bit image, the bits are often divided into three groupings: 8 for red, 8 for green, and 8 for blue. Combinations of those bits are used to represent other colors. A colour image is made when each element of the ccd array, in the camera or scanner, samples the level of a particular primary colour – Red, Green or Blue (RGB). The resultant sampling combines the information to create one full colour pixel. This full colour pixel contains three bytes (each one 8mb in depth). Three bytes per pixel (RGB) are needed so 8 × 3 = 24 bits. Brightness Brightness refers to the overall lightness or darkness of the image. Dynamic Range Dynamic range quantifies the range of brightness levels a camera’s sensor can reproduce. If your camera provides a live histogram display, you can check the brightness range in a scene before capturing it by displaying a histogram. If the brightness levels aren’t contained within the width of the graph, the highlights and shadows will be ‘clipped’ and no details will be recorded in them. Dynamic range is the ratio between the largest and smallest possible values of a changeable quantity, such in light. It is measured as a ratio, or as a base-2 (bits or stops) logarithmic value. Dynamic range are use for the luminance range of object being captured by digital camera, or the limits of luminance range that a given digital camera or film can capture, or the opacity range of developed film images, or the reflectance range of images on photographic papers. Contrast Contrast is defined as the separation between the darkest and brightest areas of the image. Increase contrast and you increase the separation between dark and bright, making shadows darker and highlights brighter. Decrease contrast and you bring the shadows up and the highlights down to make them closer to one another. Saturation Saturation is similar to contrast, however instead of increasing the separation between shadows and highlights, we increase the separation between colors. 8 Management of large sets of image data Digital image Sharpness Sharpness can be defined as edge contrast, that is, the contrast along edges in a photo. When we increase sharpness, we increase the contrast only along/near edges in the photo while leaving smooth areas of the image alone. Let’s take a look at an example with increased sharpness. Image size The physical size of an image when it is displayed on a computer screen or printed out on paper depends on two factors: the image size and the image resolution. Image size refers to the number of pixels in an image, and is measured by the number of pixels along the horizontal and vertical sides of an image, eg 600 × 400 pixels. This is the easiest (and most accurate) way to think about the size of a digital image: the number of pixels that it contains. Image resolution refers to the density at which pixels are displayed: that is, how many pixels are displayed per inch of screen or paper. File size of image is affected by three factors: pixel dimensions, image format and bit depth. File size and image quality is directly related. Artifact Artifacts refer to distortions within the image as a result of image compression or interpolation. 9 Management of large sets of image data History of digital imaging 2 History of digital imaging Early Digital fax machines such as the Bartlane cable picture transmission system preceded digital cameras and computers by decades. The first picture to be scanned, stored, and recreated in digital pixels was displayed on the Standards Eastern Automatic Computer (SEAC) at NIST (Fig. 2). The advancement of digital imagery continued in the early 1960s, alongside development of the space program and in medical research. Projects at the Jet Propulsion Laboratory, MIT, Bell Labs and the University of Maryland, among others, used digital images to advance satellite imagery, wirephoto standards conversion, medical imaging, videophone technology, character recognition, and photo enhancement. Rapid advances in digital imaging began with the introduction of microprocessors in the early 1970s, alongside progress in related storage and display technologies. The invention of computerized axial tomography (CAT scanning), using x-rays to produce a digital image of a “slice” through a three- dimensional object, was of great importance to medical diagnostics. As well as origination of digital images, digitization of analog images allowed the enhancement and restoration of archaeological artifacts and began to be used in fields as diverse as nuclear medicine, astronomy, law enforcement, defence and industry. Advances in microprocessor technology paved the way for the development and marketing of charge- coupled devices (CCDs) for use in a wide range of image capture devices and gradually displaced the use of analog film and tape in photography and videography towards the end of the 20th century. The computing power necessary to process digital image capture also allowed computer-generated digital images to achieve a level of refinement close to photorealism [15]. First Digital Image The first film photo registered by a computer and recreated in pixels – 30,976 to be exact. In 1957, Russell Kirsch, a scientist at what is now the National Institute of Standards and Technology, used a drum scanner connected to the SEAC (Standards Electronic Automatic Computer) to scan an image of his three-month-old son Walden. 10