Digital App: Binary Numbers, Bits and Bytes
The binary (computer) digit positions have values:
- 1, 2, 4, 8, 16, etc. • The value of a multiple-digit number is just the sum of the values of the marked digits as we see here.
Pixel
- A pixel, or picture element, is the smallest element in a digital image. - Digital image storage is located in a pixel, which is a two-dimensional picture element measured in the XY direction.
Analog vs. Digital Images
Analog: continuous, brightness, film density, color and for human viewing Digital: matrix of pixels, number, for computer systems.
dynamic range
Range of values that can be displayed by an imaging system; shades of gray.
Analog
Refers to a device or system that captures or measures a continuously changing signal quantity
Bits and Bytes
bit is the smallest unit of storage. one byte = grouping of 8 bits. At the smallest scale in the computer, information is stored as bits and bytes.
Increase in matrix size will ___.
decrease the pixel size to fit into the matrix. The FOV will remain the same
A digital image is represented:
in the imaging and computer system by numbers in the form of binary digits, called bits.
matrix size
is a square arrangement of numbers in columns and rows, and in digital imaging the number correspond to discrete pixel values. The larger the matrix the more pixels and more detail/quality
pixel bit depth
• 4 bits is smaller than would be used in any medical image. • Four bits would be limited to having only 16 different values (brightness levels or shades of gray).
Bits and Bytes
• Basic unit of information in computing and digital communications. • Have only one of two values, and may therefore be physically implemented with a two-state device. • The most common representation of these values are 0 and 1. • Contraction of binary digit.
What is a Digital Image?
• Broad term. • First used medically in 1970s in CT. • Any image acquisition process that produces an electronic image that can be viewed and manipulated on a computer. • Images can be sent via computer networks to a variety of locations. • Described in terms of numeric values displayed in an array of rows and columns or pixels (picture elements).
Matrix Size on Image Quality
• Illustrates the influence of matrix size on image quality • 32 x 32 matrix • "Blockheads"
Pixel size and matrix size
• More pixels do not always mean better resolution due to amount of x-ray and light scatter or both. • Not always practical to have larger matrices with smaller pixel sizes. • Larger the matrix, the larger the size of the image, and the greater the space needed for network transmission and PACS.
Characteristics of a Digital Image
A digital image begins as an analog signal. - Through computer data processing, the image become digitized and is sampled multiple times
Analog Images vs. Digital Images
- All of the medical imaging methods that produce and use digital images, must convert the images to an analog form for display and viewing. - Humans cannot get much information from just looking at a display of many numbers such as looking directly at a digital image.
Field of View (FOV)
- Changes in the FOV do not affect the size of the matrix. - Changes in matrix affect pixel size. - As the matrix increases and the FOV remains the same, the pixel size must decrease to fit into the matrix
Introduction to CR imaging with Image Acquisition
- Differentiate between analog and digital images - Describe the basic construction of a computed radiography cassette and Imaging Plate. - Identify the various layers of the imaging plate and their purpose. - Explain the process of photostimulation in the imaging plate. - Describe the process of laser beam formation. - Explain the process of reading the imaging plate. - Discuss how an image is erased from the imaging plate.
General structure of a digital image:
- Divided into a matrix of pixels. - Each pixel is represented by a series of bits.
Pixel
- Each pixel represents the x-ray intensity brightness that corresponds to a specific anatomical location - Digital image is separated into pixels, with discrete (whole numbers only) values.
Analog Images vs. Digital Images
- Humans write numbers as ten different digits, 0,1,2,3,4,5,6,7,8, and 9. - This system probably developed because we have ten fingers.
Pixel Size, Matrix Size, and FOV
- Matrix size can be changed without affecting the FOV. - FOV can be changed without affecting the matrix size. A change in either the matrix size or the FOV will change the size of the pixels.
Digital
- Recorded as multiple (2) numeric values and are divided into an array of small elements that can be processed in many different ways. - Indicates time with numbers, has a computer chip.
Introduction to DR imaging with Image Acquisition
- Review analog and digital images - Review Bits, Bytes, Pixels, Matrix, Field of View
The critical characteristics of a digital image are:
- Spatial resolution - Contrast resolution - Noise - Dose efficiency (of the receptor)
Matrix
- The image is digitized both by position (spatial location) and by intensity (gray level). - The typical number of pixels in a matrix ranges from about 512 x 512 to 1024 x 1024 and can be as large as 2500 x 2500. The size of the matrix determines the size of the pixels. - if you have a 10 x 12 and a 14 x 17 CR cassette and both have a 512 x 512 matrix, then the 10 x 12 one will have smaller pixels.
For a given FOV
- The larger the matrix size, the greater the number of smaller individual pixels. - Increasing the number of smaller pixels will improve the quality of the image. A. 64×64. B. 215 × 215. C. 1024 × 1024. D. 2048 × 2048.
pixel size
- The size of the pixel is directly related to the spatial resolution of the image. - The smaller the pixel, the higher the spatial resolution
Analog Images vs. Digital Images
- When we write larger numbers (more than one digit) the position of a digit within the number has a certain value, 1, 10, 100, 1000 - The value of a number we have written is just the sum of the values represented by each digit position. - In this example, 8000 + 500 + 30 + 4 =8,534.
Cassette based (CR)
- Workflow similar to F/S - daylight processing Uses PSP plates
Bits
- the smallest unit of data in a computer - binary digits; two different digits - They write numbers by filling in spaces (in the computer memory, on disk).
A cassette with the same matrix size 512x512, but different cassette size 10 x 12 and 14 x 17. Which cassette will have smaller pixels?
10 x 12 will have smaller pixels.
Matrix
A matrix is a square arrangement of numbers in columns and rows (XY). The numbers correspond to discrete pixel values. - Each box within the matrix corresponds to: A specific location in the image A specific area of the patient's tissue
Binary numbers (base-2)
A number system that is based on two digits, 0 and 1. 2^2.....(1,2,4,8,16,32,64,128, 256, 512.)
The number of bits or pieces of information within each pixel
A pixel with a bit depth of 8, then the number of gray tones that pixel can produce is 2 to the 8 power of the bit depth or 2^8 , or 256 shades of gray.
The range of possible values that can be written is increased by using more bits.
As shown by the equation, the range (number of possible values) is the number 2 multiplied by itself, or raised to the power, by the number of bits. • The range of possible values is doubled for each additional bit used as we will soon see. 30
A pixel with a 'bit depth' of 1 has two possible values: black or white.
Black or white
Bits are grouped into 8-bit chunks called ________.
Bytes
Digital Radiography Systems
Cassette Based Cassette-less
Will the change of FOV affect the matrix size?
Changes in the FOV will not affect the size of the matrix; however changes in the matrix will affect pixel size.
Bits and Bytes
Computer capacity is expressed by the number of bytes that can be accommodated. • 1 kB is equal to 1024 bytes • kilo is not metric in computer use. - It represents 2 to the 10th power or 1024
Digital images are:
Digital images are recorded as numbers. - The image is divided into a matrix or array of small picture elements. Each pixel is represented by a numerical value.
Bit depth range for most digital systems is between 10 and 16 or 2^10, 2^12, or 2^16 shades of gray (1024 to 65,536)
Each pixel can have a grey level between 1 (2^0) and 65,536 (2^16). - The gray level is a factor in determining the image contrast resolution
bit depth
Each pixel contains pieces or bits of information. The number of bits within a pixel is known as pixel bit depth. Ex: If a pixel has a bit depth of 8, then the number of gray tones that pixel can produce is 2^8=256 shades of gray.
Field of View
Field of view (FOV) = x-ray field. • It is the amount of body part or patient included in the image. • The larger the FOV, the more area is imaged.
Bits • However, they can only place a mark in the space (the black dot shown here) or leave the space blank (the white dot shown here). • Therefore, each digit space can have only two possible values, MARKED or BLANK.
For that reason, these are called binary meaning two digits or for short bits.
Effects of matrix size
Increasing the matrix size, from 1024 to 2048 pixels, without changing the image field of view, will produce smaller pixels. - This will generally reduce blurring and improve image detail.
Image Compression
Lossless compression is when there is no loss of image quality, and is commonly used in many medical applications. • Lossee compression results in some loss of image quality and must be used with care for diagnostic images.
Look Up Table (LUT)
Matrix of data that manipulates the values of gray levels, converting an image input value to a different output value. Specific exams have different values
Cassette-less (DR)
New workflow paradigm TFT detectors, CCD's, & PSP plates
Matrix size formula
Pixel size = image size (mm) / matrix size (pixels) Matrix size is the number of pixels along the length and width of an image. May be the same in both directions, but generally will be different for rectangular images to produce relatively square pixels.
Matrix Size on Image Quality
The higher the number of pixels, the better the resolution
Significance of Numerical Size
The larger the image numerically - the more memory and disk storage space is required. - the more time for processing and distribution of images is required.
Pixel Bit Depth
The number of bits that have been made available in the digital system to represent each pixel in the image.
In Computed Tomography
The numeric value of each pixel is a Hounsfield unit (HU) -attenuation unit used in CT Scan interpretation -characterizes the relative density of a substance
The Numerical Size of a Digital Image
The numerical size (number of bits) of an image is the product of two factors: -The number of pixels which is found by multiplying the pixel length and width of the image. -The bit depth (bits per pixel). Usually in the range of 8-16 bits, or 1-2 bytes, per pixel.
Factors Affecting Pixel Size and Image Detail
The size of a pixel (and image detail) is determined by the ratio of the actual image size and the size of the image matrix. • Image size is the dimensions of the field of view (FOV) within the patient's body, not the size of a displayed image.
In Computed Tomography
The value of the HU can be manipulated to judge the composition of the tissue represented
Effect of Field of View on Digital Image Detail
When the field of view (FOV) is reduced, without changing the matrix size, the pixels become smaller and the visibility of detail is improved.
Analog images (for human viewing)
a photograph taken with film - continuous levels of brightness; shades of gray color
Examples of Analog Images
photographs, paintings, TV images, and all of our medical images recorded on film or displayed on various display devices, like computer monitors. (for human viewing)
pixel
picture element, is the smallest element in a digital image. If you have magnify a digital picture to the point that you see the image as small squares of color, you have seen pixels.
pixels
picture elements
Change in the matrix size and/or the FOV view can change the ___.
size of the pixels
Quantization
the assignment of a numeric value for each pixel bit depth, which controls the number of grey shades, hence contrast resolution. CR Histogram. algorithm or mathematical information to evaluate the overall intensity of each procedure.
pixel bit depth
the number of bits within a pixel The number of gray shades available for image display. -Number of gray shades is 2n -Where n is the number of bits available for each pixel
Pixel Density
the number of picture elements per inch
Limitations with using binary numbers
the range of values that can be written with a specific number of bits, binary digits • Four bits can have 16 different values because there are 16 ways the four bits can be marked.
Field of View (FOV)
the x-ray field. It is the amount of body part or patient included in the image. The larger the FOV, the more area is imaged.
Voxel
• Pixels correspond to areas in the patient called voxels, volume elements. • The third dimension, "Z" direction in the matrix of pixels is the depth referred to as the Voxel. • The depth of the block is the number of bits required to describe the gray level that each pixel can take, known as bit depth.
Voxels
• Pixels correspond to areas in the patient called voxels, volume elements. • The third dimension, "Z" direction in the matrix of pixels is the depth referred to as the Voxel. • The depth of the block is the number of bits required to describe the gray level that each pixel can take, known as bit depth.
Image Matrix Size for Different Imaging Modalities
• Produces a pixel size that is compatible with the blurring and detail characteristics of each modality. • With many modalities, the matrix size can be adjusted by the operator to optimize image quality and the imaging procedure
Pixel Pitch
• The space from the center of a pixel to the center of the adjacent pixel. • Measured in microns (μm). • Determined by the detector element size or the sampling frequency.
pixel pitch
• The space from the center of a pixel to the center of the adjacent pixel. • Measured in microns (μm). • Determined by the detector element size or the sampling frequency.
Pixel Size and Digital Image Detail
• When an image is in digital form, it is actually blurred by the size of the pixel. This is because all anatomical detail within an individual pixel is "blurred together" and represented by one number. • The physical size of a pixel, relative to the anatomical objects, is the amount of blurring added to the imaging process by the digitizing of the image.
Bits
• When digital systems write numbers, they do it as a series of digits (like humans) but the digit positions have different values. • Remember our human digit positions have values: 1, 10, 100, 1000, etc.