November 1, 2013
Imaging Systems What's Inside Fundamentals
What are the basics of imaging systems? Spatial, tonal, and spectral resolution all have a say Pg A2
Input
Color Filter Arrays and Sensors Pg B6
Processing
Follow the journey of a photograph Pg C8
Output
Learn about printing technologies and halftoning processes Pg D10
Capture Process Print I’m Carol Klino - creator of this newspaper. It was made during the Imaging Systems class at Rochester Institute of Technology. The purpose is to educate the reader about the input, output, and processing of photography. The following sections will explore these three ideas in more detail. The sections will follow basic structure found in a newspaper. Fundamentals
will use photographs from a general news story while giving foundational information about imaging systems. Input will be treated like a technology section while exploring sensors and color filters in a camera during the capture of a photograph.
happens during the lifespan of a photograph. Finally, Output will use sports photography while readers can learn about printing technologies and halftoning.
the layout and photographic selections used. I would like to thank Joseph Philipson for allowWing me to use his photographs for various sections of the newspaper.
The secondary goal of this newspaper is to demonstrate the editing and layout skills necessary to creating such a Processing will be treated as a publication. With the help of travel section while discussing other students in the Imaging the imaging pipeline and what Systems class, I made all of
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Imaging Systems
Spatial Resolution How pixel interpolation affects your photographs
Spatial Resolution changes the X and Y dimensions of an image. There are multiple options using Adobe Photoshop to change the spatial resolution of a photograph through interpolation techniques. Bicubic and Bilinear interpolation produce the highest quality images, however they take a longer time to create. For the fastest output time you should use nearest neighbor interpolation. Nearest Neighbor interpolation is used to preserve hard edges in a photograph. The fastest of the three methods, however also the least accurate. Sampling is accomplished by taking the value of a pixel’s nearest neighbor, and then changing the value of that pixel to match.
as bicubic interpolation, this method is faster than enlarging a photo through the bicubic algorithm. Sampling is performed by creating new data points based on the values of the different columns and then the rows of the pixels. Bicubic interpolation is the most complicated of the three types, but also produces the most accurate results. Bicubic interpolation uses the information from an original pixel and sixteen of the surrounding pixels to determine the color of the new pixels that are created from the original pixel. It is most commonly used in situations in where a smooth gradient is desired, like portraits, because it works to fit a smooth surface to a pixel and its neighbors.
Bilinear interpolation works by sampling 4 of the surrounding pixels to create more pixels in the image. While not as accurate
Nearest Neighbor
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Bicubic Interpolation
Bilinear Interpolation
Fundamentals | November 1, 2013
Tonal Resolution How tonal levels and bit depth affect images
Tonal resolution refers to the number of gray channels in an image. An image at 3 bits per pixel distorts all of the tones in the image. Between 5 and 8 bits per pixel, the image starts to become visiblly acceptable to the human eye.
The image below shows an image with 3 bits per pixel. As you can see, the image becomes distorted and loses visual acceptability.
The image below shows an image with 8 bits per pixel. At this level, the image become more visually pleasing to our eye.
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Imaging Systems
Spectral Resolution How do color channels work within a photograph?
Spectral resolutrion can take form in many different forms. The two that we will be discussing are additive and subtractive color. Additive color relates to the three monochromatic images that a combine Red, Green, and Blue (RGB) channels in a photograph. It is most often used in computer monitors and other devices. The appearance of each channel is
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dependant upon the amount of light received by the camera’s sensor that is specific to a certain wavelength within the visible light spectrum. When equally combined, the three separate channels create white. When any two of the three additive colors are combined they create one of the subtractive colors of Cyan, Magenta, and Yellow. The subtractive colors are
commonly referred to as CMYK (the K standing for black). Subtractive colors are used in printing such as magazines. When equally combined, subtractive colors create black..
Fundamentals | November 1, 2013
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Imaging Systems
Camera Sensors CMOS CCD Charged Couple Devices
Digital sensors work by capturing light and turning it into an electronic charge. The electronic charges are converted to volts and then to digital information. A charged couple device - or CCD sensor has many photo sensors which convert light to an electronic charge. The sensors hold the charge until it is converted to voltage incremetally (one by one). There are two types of CCD sensors: interline transfer
Charged Couple Device
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Complementary Metal Oxide Semi Conductor
and frame transfer. Interline transfer CCDs are used in camcorders and have transfer shift registers along each column to shield photosites from blooming if the neighboring photosite becomes overexposed. CCD Sensors are used in many digital cameras such as the Leica M9 - used in the example photograph above. The CCD sensor produces higher quality imagery, but is much slower at converting
to the final image. This issue when combined with the fact that a CCD sensor is more expensive than it's CMOS competitor makes it impracticle for most photographers to use a camera with a CCD sensor.
Complementary Metal Oxide Semi Conductors - or CMOS sensors are more commonly used in DSLR cameras. They are faster and cheaper than CCD sensors, however they produce images with a lesser quality than the CCD. CMOS sensors have electric circuitry next to each photosite that comverts light energy into voltage, which is then processed by additional circuitry and thus converted into a digital signal.
There are active and passive versions of a CMOS sensor. The passive sensors send information from each individual pixel to an amplifier which continues to conversion process. The passive sensor is prone to producing images with higher levels of noise and lower dynamic range.
increase the dynamic range thus reducing noise levels. It is also faster than the passive CMOS sensor. For this reason active CMOS sensors are frequently used in cell phones with cameras and web cameras.
The active version of a CMOS sensor gives each pixel it's own amplifier to convert the charge to voltage which helps
Complementary Metal Oxide Semi Conductor
Input| November 1, 2013
Color Filter Array
Cameras use a filter to interpolate color patterns so they are visually acceptable to the human eye.
The image sensor of a camera does not provide complete color information. Instead it contains incomplete color samples. Therefore the sensor is overlayed with a color filter array (CFA) The CFA reconstructs the color information to create a full image. The algorithim used to complete this process is referred to as demosaicing.
Below you can see other forms of CFAs. The RGBW filter includes white or transparent cells within the pattern. These pixels absorb all of the light to produce a differnt result.
Depending on the type of CFA used, the filter produces three separate images in Red, Green and Blue as seen in the photograph above to the right. In the diagrams above, you can see the most common CFA which uses the bayer pattern. This pattern places rows of cells into green/blue and red/green patterns. Our human eye is more receptive to green wavelengths so the bayer pattern caters to that.
RGBW CFA Pattern
RGB Striped CFA Pattern
There is also the striped pattern which is the most simple. It arranged the red, green, and blue cells into vertical rows. The CMYG filter arranged cells by cyan, magenta, yellow, and green. These filters are not as accurate as a bayer pattern and therefore not as frequently used in camera systems.
CMYG CFA Pattern
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Image Processing
Follow the journey of a photograph Below you can see the typical journey a photograph takes before the output stage. Each camera and computer system varies, but the general sequence of information remains the same.
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The image above represents the scene the camera is going to capture.
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The amount of information encoded into highlights and dark points is processed so that the human eye can decipher it.
The light from the chosen scene travels to the camera.
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Above you can see an analog to digital converter. This part of the photographs journey involves translating analog data into digital numbers that our technology can understand.
The neutrals in a photograph are corrected so that grey neutral tones appear to be grey and neutral!
Processing| November 1, 2013
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The photograph is stored in a "container" file that stores all of the raw image data from the camera.
Artist Manipulation occurs. Here the photographer can edit things such as contrast and sharpness to create the image they prefer.
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The color filter array interpolation is applied to the raw data information. The CFA used in the step seen above is the standard Bayer Pattern.
The image is finally ready to be saved. The photograph is typically saved as a jpeg, TIFF, PSD, or PDF.
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Imaging Systems
Printing Technologies How do printing techniques differ?
Inkjet printing is the most widely used and most
Laser printers are mainly used in office applications.
Dye-sublimation printers are best for
Rotogravure is a type of intaglio printing process,
popular type of printing. There are 2 main types of inkjet, continuous and drop-on- demand. Dropon-demand consists of thermal and piezoelectric. Canon, Hewlett-Packard and Lexmark use the thermal technology. With thermal DOD, the ink is stored in chambers each with individual heaters. To eject a droplet the heating elements heats the ink until it vaporizes and forms a bubble. This bubble forces ink out of the cartgridge onto the paper. Piezoelectric DOD is used by Epson and Brother. Instead of a heating element behind each cartridge there is a piezoelectric material. When voltage is applied to this matterial it changes shape and creates pressure which forces ink out of the nozzle. Piezo is more expensive but can use a wider variety of inks.
photo printing. Between inkjet and laser printers, dye-sublimation is the only one that is able to print continuous tone, photographic quality images. The paper required for these printers is expensive because it must be a special type. Printing is slow and the size you can print at is restricted.
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They have a high throughput, which means they are fast, and are relatively low-cost for color. The cost per print is low but the cost per printer is higher and can range from $100 to $5000. Laser printers print text very high quality with decent photo- quality.
which involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a cylinder because, like offset printing and flexography, it uses a rotary printing press. Once a staple of newspaper photo features, the rotogravure process is still used for commercial printing of magazines, postcards, and corrugated (cardboard) product packaging.
Output| November 1, 2013
Halftoning
In non-continuous devices, half-toning must be used to print. Halftoning is a technique used to simulate continuos tone by using dots and varying them by either size, shape, and frequency. Halftoning uses pure inks such as black, cyan, magenta, and yellow to create the illusion of continuous tone. To create a halftone image, a continuous tone image is projected through a screen of dots. Areas with larger dots or more dots will be darker than areas with fewer dots, and the combination of black dots and white paper will create
shades of grey. When doing a color halftone the same process is repeated in each of the individual channels. Spatial resolution is sacrificed to gain tonal resolution.
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