Firstly this article is going to discuss pixels. Pixels, or picture elements, are dots that are used to display an image on a screen. Monitors display pictures by dividing the display screen into thousands or millions of pixels, arranged in rows and columns. The pixels are so close together that they appear connected.
These monitors have a bit rate, which controls how many greys or colours each pixel is capable of displaying.
For example;
A 1-bit system can only manage black and white because each memory bit can only be either positive or negative.
And with 24-bit each of the pixels can display sixteen-million colours;
24-bit colour is known as True Colour, because it displays every pixel colour exactly. A true-color image file records the full range of colors precisely.
True color allows more hues than the eye can distinguish, so most operating systems offer the option of 16-bit high color (Thousands of Colors on Macintosh). In high color, the monitor actually displays only 32 distinct levels of red, 32 of blue, and 64 of green. The visual difference is almost unnoticeable, but reducing the color depth to 16 bits per pixel boosts video performance. And running your computer system in high color won't affect your image data; most applications, such as Photoshop or a Web browser, still use the full 24-bit values. The data gets rounded off only when displayed on the monitor. That's why there are no high-color image file formats.
While pixels are the smallest complete element of an image, they are comprised of even smaller elements. Bit depth is the control of colour on the screen. The computers operating system must dedicate a small amount of memory to each pixel.
For example, in an RGB monitor each pixel has three dots within it: a red, blue, and green dot.
In theory these dots all converge at the same point, making them visibly seamless, but sometimes the image can appear fuzzy.
The measure of total pixels in an image is referred to as its resolution, and the higher the resolution in a small area, the more difficult it is to distinguish between individual pixels.
All images have resolution. Resolution means the pixel count in digital imaging.
An image of N pixels high by M pixels wide can have any resolution less than N lines per picture height, or N TV lines.
When the pixel counts are referred to as resolution, the convention is to describe the pixel resolution with the set of two positive integer numbers, where the first number is the number of pixel columns and the second is the number of pixel rows, for example. Another popular convention is to cite resolution as the total number of pixels in the image, typically given as number of megapixels, which can be calculated by multiplying pixel columns by pixel rows and dividing by one million.
Other conventions include describing pixels per length unit or pixels per area unit, such as pixels per inch or per square inch. None of these pixel resolutions are true resolutions, but they are widely referred to as such; they serve as upper bounds on image resolution.
The number of effective pixels that an image sensor or digital camera has is the count of elementary pixel sensors that contribute to the final image, as opposed to the number of total pixels, which includes unused or light-shielded pixels around the edges.
The count of pixels isn't a real measure of the resolution of digital camera images, because colour image sensors are typically set up to alternate colour filter types over the light sensitive individual pixel sensors. Digital images ultimately require a red, green, and blue value for each pixel to be displayed or printed, but one individual pixel in the image sensor will only supply one of those three pieces of information. The image has to be interpolated to produce all three colours for each output pixel.
But only a certain kind of images are made up of pixels. These images are called Raster images.
Raster images, also known as Bit map images are a way to represent digital images. A raster image represents an image in a series of bits of information which translate into pixels on the screen. These pixels form points of colour which create an overall finished image.
When a raster image is created, the image on the screen is converted into pixels. Each pixel assigned a specific value which determines its colour.
The raster image takes a wide variety of formats, such as;
Bmp – a BMP image, also known as a bitmap image file, is a raster graphics image file format that is used to store digital images. BMP images use no compression.
JPEG - A JPEG, or Joint Photographic Experts Group, is commonly used for storing digital photos since the format supports up to 24-bit colour.
When a raster image is created, the image on the screen is converted into pixels. Each pixel assigned a specific value which determines its colour.
Bmp – a BMP image, also known as a bitmap image file, is a raster graphics image file format that is used to store digital images. BMP images use no compression.
JPEG - A JPEG, or Joint Photographic Experts Group, is commonly used for storing digital photos since the format supports up to 24-bit colour.
The degree of compression can be adjusted, allowing a selectable trade-off between storage size and image quality. JPEG has a lossy compression, which means it can compress files so that they are smaller, but the files loose some colour and information.JPEG typically achieves 10:1 compression with little perceptible loss in image quality.
PNG - The PNG, or Portable Network Graphics, file format supports true colour which is 16 million colours. The PNG file excels when the image has large, uniformly coloured areas. The lossless PNG format is best suited for editing pictures. Indexed-colour, grayscale, and true colour images are supported, plus an optional alpha channel. PNG is designed to work well in online viewing applications like web browsers so it is fully stream able with a progressive display option. It is robust, meaning it provides both full file integrity checking and simple detection of common transmission errors.
GIF – GIF, or Graphics Interchange Format, is limited to an 8-bit palette, or 256 colours. This makes the GIF format suitable for storing graphics with relatively few colours such as simple diagrams, shapes, logos and cartoon style images. The GIF format supports animation and is still widely used to provide image animation effects. It also uses a lossless compression that is more effective when large areas have a single colour, and ineffective for detailed images or dithered images
TIFF - The TIFF, or Tagged Image File Format, is a flexible format that normally saves 8 bits or 16 bits per colour for 24-bit and 48-bit totals, usually using either the TIFF or TIF filename extension. TIFF's flexibility can be both an advantage and disadvantage, since a reader that reads every type of TIFF file does not exist. It can be lossy and lossless as some offer relatively good lossless compression for bi-level, black and white, images.
GIF – GIF, or Graphics Interchange Format, is limited to an 8-bit palette, or 256 colours. This makes the GIF format suitable for storing graphics with relatively few colours such as simple diagrams, shapes, logos and cartoon style images. The GIF format supports animation and is still widely used to provide image animation effects. It also uses a lossless compression that is more effective when large areas have a single colour, and ineffective for detailed images or dithered images
TIFF - The TIFF, or Tagged Image File Format, is a flexible format that normally saves 8 bits or 16 bits per colour for 24-bit and 48-bit totals, usually using either the TIFF or TIF filename extension. TIFF's flexibility can be both an advantage and disadvantage, since a reader that reads every type of TIFF file does not exist. It can be lossy and lossless as some offer relatively good lossless compression for bi-level, black and white, images.
All these images have either lossy, lossless, both or no compression. But what is lossy and lossless compression?
Lossy methods are especially suitable for natural images such as photographs in applications where minor loss of fidelity is acceptable to achieve a substantial reduction in bit rate.When files are compressed with lossy compression, they tend to look blurred. This is because when, for example, a file is converted into a JPEG file so it can be compressed and made smaller, the compression causes it to loose colour and information.
Lossless compression means that the picture can be reconstructed from the compressed file, so that it doesn’t lose colour or information from the picture, like it would if it was lossy compressed. Lossless compression is preferred for archival purposes and often for medical imaging, technical drawings, clip art, or comics, because the picture looks more clear and professional.
Here is an image example showing the comparison between Lossy and Lossless;
But if only Raster Images have pixels, what is the other type of image that doesn't use pixels?
These non-pixel images are called Vector Images.
Image compression can be either lossy or lossless.
But if only Raster Images have pixels, what is the other type of image that doesn't use pixels?
These non-pixel images are called Vector Images.
Vector graphics is based on images made up of vectors which lead through locations called control points. Each of these points has a definite position on the x and y axes of the work plan. Each point is a variety of database, including the location of the point in the work space and the direction of the vector. Each track can be assigned a colour, a shape, a thickness and also a fill. This does not affect the size of the files in a substantial way because all information resides in the structure.
Vector images can be resized to any size, and the image will still remain clear, unlike raster images where the image would become pixelated if it’s resized big enough.
Vector images can have fake cartoon look. This is due to the fact that they are unable to depict the continuous subtle tones of a photograph.
The difference between vector and raster graphics is that raster graphics are composed of pixels, while vector graphics are composed of paths.
Because vector graphics are not made of pixels, the images can be scaled to be very large without losing quality.
Raster graphics, on the other hand, become "blocky," since each pixel increases in size as the image is made larger. This is why logos and other designs are typically created in vector format -- the quality will look the same on a business card as it will on a billboard.
Here is a picture example showing the difference between a Vector and Raster, or Bitmap, image:
Greyscale
In photography and computing, a greyscale digital image is an image in which the value of each pixel is a single sample, that is, it carries only intensity information. Images of this sort, also known as black-and-white, are composed exclusively of shades of grey, varying from black at the weakest intensity to white at the strongest.
Grayscale images are distinct from one-bit bi-tonal black-and-white images, which in the context of computer imaging are images with only the two colours, black, and white
A raster image, such as a gif or jpeg, is an array of pixels of various colours, which together form an image. A vector graphic, such as an .eps file or Adobe Illustrator file, is composed of paths, or lines, that are either straight or curved.The data file for a vector image contains the points where the paths start and end, how much the paths curve, and the colours that either border or fill the paths.
Because vector graphics are not made of pixels, the images can be scaled to be very large without losing quality.
Raster graphics, on the other hand, become "blocky," since each pixel increases in size as the image is made larger. This is why logos and other designs are typically created in vector format -- the quality will look the same on a business card as it will on a billboard.
Greyscale
In photography and computing, a greyscale digital image is an image in which the value of each pixel is a single sample, that is, it carries only intensity information. Images of this sort, also known as black-and-white, are composed exclusively of shades of grey, varying from black at the weakest intensity to white at the strongest.
Grayscale images are distinct from one-bit bi-tonal black-and-white images, which in the context of computer imaging are images with only the two colours, black, and white
Grayscale images are also called monochromatic, denoting the presence of only one, mono, colour, chrome.
Grayscale images are often the result of measuring the intensity of light at each pixel in a single band of the electromagnetic spectrum (e.g. Infrared, visible light, ultraviolet, etc.), and in such cases they are monochromatic proper when only a given frequency is captured.
RGB
The RGB colour model is an additive colour model in which red, green and blue light is added together in various ways to reproduce a broad array of colours.
The name RGB comes from the initials of the three additive primary colours, red, green, and blue.
The main purpose of the RGB colour model is for the sensing, representation, and display of images in electronic systems, such as televisions and computers, though it has also been used in conventional photography
Before the electronic age, the RGB colour model already had a solid theory behind it, based in human perception of colours.
RGB is a device-dependent colour model: different devices detect or reproduce a given RGB value differently, since the colour elements (such as phosphors or dyes) and their response to the individual R, G, and B levels vary from manufacturer to manufacturer, or even in the same device over time. Thus an RGB value does not define the same colour across devices without some kind of colour management.
Typical RGB input devices are colour TV and video cameras, image scanners and digital cameras.
YUV - Luminance and Chrominance
YUV is a colour space typically used as part of a colour image pipeline. It encodes a colour image or video taking human perception into account, allowing reduced bandwidth for chrominance components, thereby typically enabling transmission errors or compression artefacts to be more efficiently masked by the human perception than using a "direct" RGB-representation.
Image Capture
Image Capture refers to the capturing
of images through different devices. These devices include;
- Digital Cameras
- Scanners
Devices such as digital cameras focus light onto a semiconductor to
create a digital image.
This basically means, in the case of digital cameras, that they directly
sample the original light that bounces off your subject, immediately breaking
that light pattern down into a series of pixel values. Within all cameras there
are a series of lenses that break down the light to create an image, but
Digital Cameras focus the light on to a Semiconductor device that records it electronically,
rather than a tape like with non digital cameras.
Optimising
Optimising means changing both the visual and file size of an image in order for it to be used in other programmes.
For example, an image taken from the internet and intended to be put into a powerpoint may be too big to actually fit into Powerpoint.
Optimising
Optimising means changing both the visual and file size of an image in order for it to be used in other programmes.
For example, an image taken from the internet and intended to be put into a powerpoint may be too big to actually fit into Powerpoint.
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