Download
Download Presentation
Loading in 2 Seconds...
Digital Imaging and Image Analysis Bozzola and Russell – Chapter 18 http://www.uga.edu/caur/maflect.htm Lascaux Cave in Southern France 15,000 years B.C.E. For thousands of years mankind has been trying to convey to others his observations of nature through the use of images.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Digital Imaging and Image Analysis
Bozzola and Russell – Chapter 18
http://www.uga.edu/caur/maflect.htm
Lascaux Cave in Southern France
15,000 years B.C.E.
For thousands of years mankind has been trying to convey to others his observations of nature through the use of images.
1672-1723
1787-1851
Photography or “light writing”
is the process by which an image is recorded without the aid of drawing.
1787-1851
Daguerre’s method consisted of treating silver-plated copper sheets with iodine to make them sensitive to light, then exposing them in a camera and "developing" the images with warm mercury vapor. Such images came to be known as Daguerreotypes
Joseph Nicéphore Niépce World’s first photograph
1826
John Benjamin Dancer
1812-1887
In 1840, he showed first photomicrograph (actually a Daguerreotype) of a Flea using a gas illuminated microscope and a camera lucida.
In the mid-1800’s photographers learned to apply a silver halide emulsion to glass plates. These “negatives” could then be used multiple times to create many photographs of a single image.
Until the 1960’s all TEMs also used glass plates for capturing images. The scientists would have to apply the emulsion to the plates themselves as these did not come ready made from the manufacturer.
Modern photography still uses silver halide grains embedded in an emulsion but the base is no longer made of glass.
Some of the halide grains will become exposed due to the energy of the transmitted electrons striking them. Upon development these exposed grains become deposited as metallic silver. This is the “latent” image. After fixation unexposed (and thus undeveloped) silver grains are removed from the emulsion by a process known as fixation.
A black and white photograph is nothing more than a two dimensional arrangement of black (silver grains) and white (paper backing from which grains have been removed) arranged in such a way that they create an image.
Optical: Mechanical manipulation
(lenses, enlargers, etc.)
Analog: Electronic manipulation
Digital: Computer manipulation:
Image as a data matrix
Optical: Brightness, contrast, enlargement,
cropping, dodging & burning
Analog:
Digital:
Optical: Brightness, contrast, enlargement,
cropping, dodging & burning
Analog: Brightness, contrast.
Digital:
Optical: Brightness, contrast, enlargement,
cropping, dodging & burning
Analog: Brightness, contrast.
Digital: Brightness, contrast, enlargement,
cropping, dodging & burning, non-
linear display, contrast stretching,
erosion & dilation, edge
enhancement, etc.
Brightness: The location of a visual perception along the black to white continuum
Bright
Dark
Contrast: The range of optical density and tone on a photographic image (or the extent to which adjacent areas on a CRT differ in brightness.
High
Low
As contrast is increased the overall brightness of the image appears to increase in some areas and decrease in others
In photographic image processing brightness is modified by exposure which is a function of illumination intensity X time. The longer the time and/or the more intense the illumination the brighter the image will be.
In analog processing brightness is increased by increasing the signal going to each pixel
In digital processing brightness is increased by increasing the numerical value of each pixel by an equal amount.
In photographic image processing contrast is controlled by the size of silver grains in the emulsion, the larger the grains the greater the contrast.
In analog processing contrast is increased by varying the ranges of signal to each pixel.
In digital processing contrast is increased by expanding the differences in numerical values between the maximum and minimum pixels.
Optical: Stored as negatives (original) or
prints (second generation)
Analog: Stored as video (original) or copy (second generation)
Digital: Stored as computer data file (original and multiple copies all first generation)
Optical: Transmitted by distribution of prints (second generation) or publication (fourth generation)
Analog: Transmitted by distribution of video tapes (second generation) or broadcast (third generation)
Digital: Transmitted by file copying and transfer (all first generation)
A digital image is nothing more than a data matrix that assigns both a value and a location to each picture element (pixel) in the image
When considering the “resolution” of a digital image we need to consider both of these aspects; value of the pixel and its position in the data matrix
“Spatial” resolution is defined as the number of pixels used to create the image or more simply the total number of pixels in the matrix.
A digital image from a typical SEM or TEM is often 2K x 2K format whereas a photographic negative from a TEM is closer to 8K x 6K if one were to count silver grains as pixels.
Pixel resolution refers to the number of pixels that comprise the image regardless of how large the image is. A typical computer monitor has a 1024 x 768 pixel resolution whether it is a 15” or 21”
Dots per Inch or “DPI” refers to the number of pixels per linear inch in the final image. Thus the DPI of a given image decreases as the size of the final image increases.
“Grey level” resolution refers to the range of values that each pixel might have. The greater the value range, the greater the grey level resolution.
Bit = a unit of binary information either a “0” or a “1”
Byte = a string of eight bits
KiloByte = 1000 Bytes or 8000 bits
MegaByte = 1000 KB
One bit can code for only two values or states (0) or (1)
Two bits can code for four states: (0,0) (0,1) (1,0) or (1,1)
Three bits for eight and so on....
One Byte can code for 28 or 256 different states (0,0,0,0,0,0,0,0) (0,0,0,0,0,0,0,1)...
This is often referred to as the “bit depth” of an image and it limits the range of pixel values that can be displayed in the image.
1 8 24
The average human eye can perceive fewer than 100 different shades of grey between absolute white and absolute black. Thus an 8-bit image, with a possible 256 different levels of grey is more than sufficient to display any typical B&W image.
Color digital images can also be based on
8-bit format but in this case a total of three separate pixels (Red, Green, & Blue) are combined for a 24 bit-depth range of colors.
28 x 28 x 28 = 224 =
RGB
16,777,216 different colors
This is sufficient to render very sophisticated and realistic graphics. The latest Nintendo Game Cube advertises a pixel depth with 24-bit color.
The best digital capture devices are capable of capturing images in 12 or even 16-bit (216) grey scale format and are cooled to reduce the effects of noise from the electronics.
Micro Luminetics Cryocam
The data storage demands increase dramatically depending on the spatial and grey-scale resolution:
512 x 512 8-bit image = 262 KB
1024 x 1024 8-bit = 1,049 KB
1024 x 1024 12-bit = 1,573 KB
2048 x 2048 16-bit = 8,389 KB
The number of possible pixel values increases dramatically with relatively modest demands on data storage.
8-bit image 256 shades of grey
12-bit image 4096 shades of grey
16-bit image 65,536 shades of grey
If humans can only see ~100 shades of grey why bother with so much data?
8-bit 12-bit 16-bit
Bit-depth can be an important aspect of color images. The human eye can discern many different colors and hues so the “dynamic range” of a color image is important.
Bit-depth can be an important aspect of color images. The human eye can discern many different colors and hues so the “dynamic range” of a color image is important.
But Electron Microscopy is B&W
so who cares!
