Imaging Systems Understanding the Imaging Systems Process from Camera Capture to Display Print

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1 Imaging Systems Understanding the Imaging Systems Process from Camera Capture to Display Print Ira Morris

2 Introduction, 5 Chapter One, 7 Resolution, 9 Spatial Resolution, 11 Tonal Resolution, 13 Spectral Color Resolution, 15 Temporal Resolution, 17 Resolution Calculation, 19 Chapter Two, 21 CCD, 22 CMOS, 23 CFA, 24 Scanners, 25 Chapter Three, 27 Image Processing Pipeline, 28 Chapter Four, 35 Printer Technologies, 36 Monitor Display Technologies, 38 Halftoning, 40 DPI & PPI, 41 Diagram References, 42

3 Introduction You ve got to push yourself harder. You ve got to start looking for pictures nobody else could take. You ve got to take the tools you have and probe deeper. - William Albert Allard Photography has changed dramatically with advancements in digital technology. Photographs must be captured and processed faster and more efficient. Clients expect a finished product within days and sometimes within hours. Competition is growing with the decreasing price of high-end digital cameras. A solid knowledge base of the photographic process, from capture to output, is essential to the growth of a professional photographer. Understanding how an image transitions from creative vision to final product, whether that is a print or a monitor, is the first step in professional consistency and artistry. This book is designed to enhance the knowledge needed to pursue a professional career in the Photography industry. - Ira Morris 4 5

4 Chapter One Chapter One Resolution Chapter One Spatial Resolution Spectral Resolution Tonal Resolution Temporal Resolution Resolution is best described by breaking down each component that determines an image size. Understanding this process will prepare a professional for proper storage space during image capture and archiving. 7

5 Chapter One Resolution Resolution Image resolution refers to the collective information that represents the content within an image. Resolution is widely used in unison with pixels but is much more. Pixels are small square light meters, which capture the light at different levels of brightness ranging from 0 (black) to 255 (white). Resolution- Refers to the collected information within an image. Content collected by four types of resolution; Spatial, Spectral, Tonal, Temporal. Four types of resolution represent the collective information that creates a file. Spacial, Spectral, and Tonal resolution represent a still image while the fourth, Temporal, allows for the moving image or video. Spatial Resolution is the main factor in capturing clarity. This is not directly linked to number of pixels. The more pixels does not always factor into a better image. Spatial Resolution refers to the number of independent pixel values per unit length. This means a larger sensor size with larger pixels (smaller mega-pixel calculation) could produce a better quality image. Spectral Resolution is the ability of the sensor to define fine wavelength intervals across the visual electromagnetic spectrum. Color photography is tailored to be sensitive to the Red, Green, and Blue wavelengths. This causes three channels, which will be explained in more detail later in the chapter. Tonal Resolution is a calculation of the number of gray levels within an image. Remember, a color image is colored gray levels. All images are represented on a gray scale from Most cameras are 8 bits/pixel. This is 256 shades of gray and represents the limit for the human eye. Temporal Resolution defines the refresh rate on the monitor. The monitor must be refreshed at periodic intervals and the higher the refresh rate, the better the image will look. This particular resolution will only apply to video and can be omitted in regards to still images. Spatial Resolution- Measure of how closely lines can be resolved in an image. Spectral Resolution- Defines wavelength intervals within an image. Usually 3; Red, Green, and Blue (RGB). Tonal Resolution- Represents the gray levels or brightness levels within an image. Temporal Resolution- Precision of a measurement in respect to time. 9

6 Chapter One Original Image (400%) Spatial Resolution Remember that spatial resolution is not completely influenced by pixel count, as shown in the example to the right. An image must be captured at a high resolution in order for the image to be high resolution. Increasing pixel/inch will directly impact the size of the image. The example to the right shows two of the same size images but a higher pixel count on the left. This causes a blurring affect if the image size is not reduced. The same affect will happen when enlarging an image. The size of the image will influence the pixel count needed to maintain clarity. For example, an 11x14 image at 300 dpi (Digital Pixels per Inch or Resolution) will give similar clarity as an 16x21 image at 206 dpi. This allows for a larger print at a lower resolution. Depending on the usage of the image this may be acceptable. Increasing spatial resolution gives a better rendition of the detail (less pixelation ). Image at left has a higher pixel count than the one to the right, but is still of worse spatial resolution. Spatial Resolution There are three ways to increase or decrease the size of an image and keep the same dpi. There will be a loss of detail but knowing which one to use will help in certain situations. Bicubic, Nearest Neighbor, and Bilinear use an interpolation process that either replicate pixels (increase size) or eliminate pixels (decrease size). Interpolation- Imaging method to increase (or decrease) the number of pixels in a digital image. Bicubic Interpolation (500%) Nearest Neighbor Interpolation (500%) Bicubic Interpolation is the most widely used and samples an area of 4x4 around each pixel. This process usually gives a slightly smoother affect due to the larger amount of pixels being used (16). This process also renders at a slightly slower rate, which can be important when processing a larger amount of images. Bicubic Interpolation- Interpolation method which uses data from all eight pixels surrounding the pixel being worked on. Bilinear Interpolation is similar to Bicubic except for the amount of pixels being sampled. Bilinear uses a 2x2 grid and a smaller amount of pixels (4). In most cases it is hard to see the difference between bilinear and bicubic and using bilinear can be beneficial when processing a large amount of images. Bilinear Interpolation- Interpolation method which uses data from the four pixels at the sides (not at the corners) of the pixel being worked on. Nearest Neighbor Interpolation is the simplest method and basically makes the pixel larger. If the image is enlarged 200%, one pixel will be enlarged to a 2x2 area and the color of the new pixel will remain the same as the original. This process is helpful when enlarging a digital image for closer examination but will not be suitable for enlarging photographic images due to the jagged edges created. Nearest Neighbor Interpolation- Interpolation method that selects the value of the nearest point and does not consider the values of neighboring points Bilinear Interpolation (500%) 10 11

7 Chapter One Tonal Resolution Tonal Resolution 8 Shades of Gray 3 bits/pixel Tonal resolution represents the number of gray levels in an image. A camera capturing an image at 8 bits/pixel is recording 256 shades of gray. This is easily calculated by using the equation 2 bits/pixel or in this case 2 8. A 4 bits/pixel camera would be capturing 16 shades of gray (2 4 =16). As can be seen to the left, the lower the bits/pixel the more undesirable the image. Examples of Tonal Quality as read on the Histogram Dark Image Low Key The human eye can see a range of 256 shades of gray. A camera with 8 bits/pixel will have smooth transitions of tones throughout each photograph Gray Levels Light Image High Key 4 bits/pixel 16 Shades of Gray Brightness level is also directly impacted by shades of gray. Recording more information within the higher numbered shades of gray (255 or white) will result in a brighter image. This can be easily understood when looking at a histogram Gray Levels High Contrast Pixel Count Gray Levels Gray Levels Shades of Gray 5 bits/pixel The spike to the right shows a larger pixel count or detail within the brighter gray scale range. This is mainly due to her brighter skin tone and the background. The smaller spike to the left of the histogram shows the lower pixel count in the darker areas of her shirt. This histogram also shows a good contrast range due to extending from close to 0 through about 245. Good Contrast Gray Levels bits/pixel 256 Shades of Gray 13

8 Chapter One Spectral Color Resolution Color can be generated in many ways. The most common process of capture and working color space is RGB. This is known as the additive process. The example to the left shows the red, green, and blue additive colors. When these colors are individually combined they form the subtractive process (Cyan, Magenta, Yellow) or CMYK. The K represents black. CMYK color space is used in printing and most images need to be converted in an editing program. (R) (G) (B) The image is captured with a red gel on camera right and a blue gel on camera left. Brighter areas can be seen with each specific color channel. Spectral/Color Resolution The camera captures an image with three monochrome signals. This creates three channels, which will influence the amount of brightness that is represented within each channel. In simple terms, a sensor is a combination of millions of light meters called pixels. Pixels record light on a gray scale and is converted to color from the three monochrome signals. These three channels are formed by red, green, and blue colored filters. The filters will only let the light pass that is the specific color. A red frequency from the visual spectrum will only pass through the red filter. See examples of these three color channels to the right. There are multiple color spaces and each one has a different gamut. Some capture and allow you to work with a wider range of colors, as can be seen in the figure to the right. These color spaces are device dependent and will be limited to the device being used. Gamut- Or color gamut, is a certain complete subset of colors. Original Image +75% Contrast in RGB Color Space +75% Contrast in L*a*b* Color Space 14 The most complete color space is referred to as L*a*b* and is designed to approximate human vision. This color space is device-independent and was created to be used as a reference. This color space is excellent for accurate color balance corrections by modifying output curves in the a* and b* components. As well as color balance, modifying the L* contrast will result in a better conversion due to not adjusting the color. This process is shown in the images to the left. In the RGB or CMYK color spaces, which model the output of physical devices rather then human visual perception, these similar affects can only be done with the help of blending options in editing applications. L*a*b* is the most complete color space. L* reflects the brightness of a color from white (+L*) to black (-L*). a* represents where a color falls between red (+a*) and green (-a*). b* represents where a color falls between yellow (+b*) and blue (-b*). 15

9 Chapter One 7 still frames removed from a fps (1080p) video capture. The time stamp has not changed from the first image to the last image due to there being close to 30 still frames each second. Temporal Resolution With the rise of video production in DSLR cameras, it is appropriate to understand Temporal or Time Resolution. Temporal Resolution has different applications when referring to different devices. In regards to understanding resolution capture, we will focus on the recording of the data. Temporal Resolution also refers to refresh rate when regarding a television or computer screen. Temporal Resolution Temporal Resolution is measured in frames/sec or fps. A typical DSLR will capture video data at fps and can usually be adjusted to capture different fps (24 fps or fps). High-end video cameras can capture data upwards of 1000 fps and this will allow for smooth slow motion when adjusted down to a lower fps fps is the North American and Japan standard for television and 25 fps is the European standard, along with many other countries. 30 fps is widely used in reference to fps. This is rounded up for convenience and is usually meant as fps. 30 fps is rarely used. This is also done with 60 fps, which is meant as Video capture at high definition (HD) is categorized with the numbers 720 and These numbers refer to the vertical resolution or horizontal lines that are within the frame. These numbers are also coupled with its vertical lines; 720x1280 (921,600 pixels of resolution), 1080x1920 (2,073,600 pixels of resolution) seems like the obvious choice with over a million more pixels of resolution but there are other factors that will influence the quality. There are two different forms of 1080 HD capture, 1080i and 1080p. The i stands for interlaced and the p stands for progressive scan. When an image uses interlaced it scans twice, once for the even horizontal lines and again for the odd horizontal lines. Because of persistence of vision these two fields merge in our brains to form one frame. Depending on the video being captured this can be an issue. Fast moving objects can create unwanted blur due to the even and odd lines not matching exactly. It would be better to capture sports in 720p instead of 1080i, definitely since 1080p would use too Persistence of Vision- Phenomenon of the eye by which an afterimage is thought to persist for approximately one twenty-fifth of a second on the retina. Interlaced capture showing scanning process of first image (even) then second image (odd) 16 17

10 Chapter One 7320 Horizontal Lines Resolution Calculation Calculating the file size can be very useful when determining appropriate storage space needed during an assignment. Understanding the different forms of resolution and then being able to use this information in practical situations will encourage job opportunities and enhance problem solving skills. Camera Data Make Phase One A/S Model P40+ Focal Length mm Shutter Speed 1/125 sec F/stop f/6.3 ISO 100 Resolution Calculation 5484 Vertical Lines Spatial Resolution Vertical Lines x Horizontal Lines Image Size = X Tonal Resolution 8 bits/pixel = 1 byte (256 Gray Levels) X Spectral Resolution 3 Channels (RGB) (5484 x 7320 x (1 byte) x 3) (1024 x 1024) X Temporal Resolution Frames per second (fps) Optional Spatial resolution information is determined with the camera and will be different between images. This information can be found in the meta-data, which I have added to the right. Spatial Resolution can be found under Dimensions. Tonal Resolution is under bit depth and has to be switched to bytes in order to calculate it into megabytes. 8 bits represents 1 byte. When dividing (1024 x 1024) bytes will be recalculated to megabytes. If the bytes were divided by (1024) then it would be recalculated to kilobytes. Spectral Resolution can be found under Color Mode. RGB represents the 3 channels; Red, Green, Blue. The spatial resolution of an image is recorded 3 separate times. This is calculated by the (x 3) in the first equation. File Properties Document Type Tiff Image Dimensions 5484 x 7320 Dimensions (In) 22.9 x 30.5 Resolution 240 pixels/inch Bit depth 8 bits/pixel Color Mode RGB Color Profile Adobe RGB 1998 File Size M Bytes File size is different here because of the added meta-data (copyright info, etc.) Image Size = 120,428,640 (bytes) 1,048,756 Temporal Resolution was not calculated in the equation to the left due to it being a still image. Still images can omit this step but in reference to video this will need to be calculated. The example below shows the equation that will be used when determining video size. The is the frames per second and increases the size tremendously due to having almost 30 still images. The resolution is changed to show full HD. Byte Equivalents 8 bits = 1 byte 1024 bytes = 1 kilobyte 1024 kilobytes = 1 megabyte Image Size = ~ Mega Bytes Video Size = (1920 x 1080 x (1 byte) x 3 x 29.97) (1024 x 1024) Video Size = ~ MBytes/ Sec 18 19

11 Chapter Two Chapter Two Chapter Two Digital Input Electronic Sensors; CCD, CMOS Color Filter Array; CFA Scanners; CCD, CIS Digital images are captured on an image sensor, which is a device that converts an optical image into an electronic signal. Most digital cameras either use CCD (charged-coupled device) or CMOS (complementary metal-oxide-semiconductor). 21

12 Chapter Two CCD CMOS Digital Input Charge-Coupled Device- A high-speed semiconductor used chiefly in image detection. Photo-diodes (Pixels) Vertical shift registers Blooming effect Horizontal shift register A charge-coupled device (CCD) is a device used to transfer photons (light) into an electrical charge. When light bounces off of a subject and travels through the lens of a camera it is carrying different variations of brightness. This reaches the photo-diodes (pixels) and is then transformed into an electrical charge. Different intensities are varied across the pixels due to the amount of light that reaches them. A darker area on the subject will cause less light to reach that portion of the pixels, which will result in a smaller electrical charge and converted to binary code that is read as a darker area. The CCD is comprised of Vertical and Horizontal shift registers. The pixels are struck with light and the electrical charge is transferred down to the horizontal shift, one row at a time. This analog information is then cycled through an output amplifier and into an analog to digital converter where the electrical charge is transformed into a binary code that can be read by a computer. Think of pixels as a bucket and photons as rain. The more rain that fills the bucket the more information that is captured. The buckets are then transferred down the vertical shift register and then across to the output amplifier by the horizontal shift register. This process is performed one row at a time at a high rate of speed. The CCD is a major technology for digital imaging and is used in cameras where high quality image data is required. Professional, medical, and scientific applications commonly use the CCD sensor for capture where a great amount of detail and quality are necessary. A CCD sensor can cause a blooming effect, where a light source has overloaded the sensitivity of the sensor and caused the sensor to bleed the light onto neighboring pixels. This usually occurs when photographing a subject against a bright background. A complimentary metal oxide semiconductor (CMOS), also known as active-pixel sensor (APS), performs the same task as a CCD. The difference between the two sensors has to do with the pixel itself. In a CMOS APS sensor the pixel consists of a photodetector, a floating diffusion, a transfer gate, reset gate, selection gate and source follower readout transistor. This is known as the 4T cell but more often the 3T cell is used and in the 3T cell the transfer gate is not present. The CMOS sensor gets its name from the way it is manufactured. They are cut from the CMOS wafer, which is cheaper to produce then the CCD wafer, has less power consumption, and has more involved circuitry along side the photo-diode (pixel). This circuitry along side the photodiode can cause noise due to portions of the light hitting the transistors. The biggest advantage with the CMOS sensor is that it is typically less expensive. It is also immune to the blooming effect caused by overloading the sensitivity of the CCD. A major disadvantage to the CMOS is that it can cause a rolling shutter effect, where the image seems to tilt to one side. This is caused because the CMOS captures one row at a time at approximately 1/60 th, depending on refresh rate. CMOS APS is most commonly used in cell phone cameras, web cameras and is rising in high-end DSLR production. Cost Power Noise Maturity Extended Functionality CCD Expensive to produce Consumes up to 100x more power High quality, low noise Produced for longer period Technically feasible CMOS Complimentary Metal Oxide Semiconductor- An image sensor consisting of an integrated circuit containing an array of pixel sensors, each pixel containing a photodetector and an active amplifier. Inexpensive to produce Low power consumption Susceptible to noise (getting better) Less mature but equal in lower resolution Circuitry easily incorporated on same chip 22 23

13 Chapter Two CFA Scanners Digital Input Color Filter Array- Tiny color filters placed over the pixel sensors to capture color information. Bayer Pattern- A color filter array for arranging RGB color filters on a square grid of photosensors (pixels). Original Sensor Array CFA refers to Color Filter Array also known as mosaic sensor. It is important to understand that a sensor captures raw data in grayscale. It is the job of the color filter array to create color images from the raw grayscale capture. Most cameras use a Bayer pattern, which is red, green, and blue, while some will use CMY (cyan, magenta, and yellow) because they transmit more light. It is also possible to add a fourth color to the mix. The fact to understand is that no matter what color arrangement is used, each element captures only one color. The red filter elements create a grayscale value proportionate to the amount of red light reaching the sensor. This is continued with green and blue or any color arrangement used. Raw files contain two different types of information, the pixel data and metadata. Metadata is essentially the data about the data. Metadata records camera information in regards to image size, focal length, shutter speed, f-stop, etc. Metadata also includes a decoder ring, which is used by the raw converter to convey the arrangement of the color filters on the sensor, so it tells raw converters which color each pixel represents. The raw converter then uses this information to convert the grayscale raw capture into a color image. Scanners are fundamentally the same device as cameras with one difference, they come equipped with their own light source. Scanners have been used to create images as well as copying existing printed photographs for use of documentation and artistry. Two common flatbed scanners are CCD and CIS scanners. A CCD scanner has thousands of CCD elements. The scanner shines through red, green and blue filters and the reflected light is directed into the CCD array assisted by a series of mirrors and lenses. The document has to be 30cm from the sensor in order to transfer a standard 8.5x11 page onto a 1in CCD sensor. A CIS (contact image sensor) was developed to improve upon deficiencies of the image sensor lens reduction system found in CCD scanners. Document distance has been reduced to 2cm since the CIS module length is a direct one-to-one relationship. Red, Green and Blue LEDs are used to produce white light and the lenses and mirrors are replaced with a single row of sensors extremely close to the source image. CIS scanners are thinner and lighter, more energy efficient and cheaper to manufacture but unable to produce equal image quality as of yet. CCD Scanner Photo-multiplier tube- A rotating drum scanning one row of pixels at a time. Used in high-end scanners. PPI- Pixels per Inch. Will be explained in Chapter 4 (output). CIS Scanner Desktop film scanners regenerate the image stored on film. Light is transmitted through film and an electrical signal is generated. The electrical signal is fed to an electronic sensor like silicon (CCD) or a PMT (photo-multiplier tube). The resolution is capable of reaching ppi, which is needed to make the smaller size of a negative into a larger print. Incomplete Red, Green, and Blue Channels Raw Converter RGB File 24 25

14 Chapter Three Chapter Three Digital Processing Chapter Three Imaging Processing Pipeline Imaging processing pipeline is the steps an image takes from capture to output. Every digital image takes the same path with varying degrees depending on camera manufacturer. Depending on camera settings, an image can take two paths; JPEG and/or RAW. 27

15 Chapter Three In Camera Processing Capturing images with camera set to JPEG compression Image Processing Pipeline Image Processing Pipeline B&W One Channel Capture Pixel Defect Correction Photo Response Non-Uniformity RAW Data Color Filter Array Interpolation - RGB Neutral White Balance Camera Profile; srgb, A-RGB, ProPhoto Gamma Correction Exposure Correction Set White Point Exposure Correction Set Black Point Stored as JPEG. Camera has most control over file adjustments. File only capable of minor manipulation. Creates a Color Correction Profile. Used in both JPEG and RAW pipelines. Tone Corrections Sharpening / Noise Reduction Lens Correction Vignetting/ Aberrations Output Spectral Power Distribution Light Source Characteristics MACBETH Color Checker Human Eye Characteristics Standard Human Observer Camera Profile; srgb, A-RGB, ProPhoto. RAW Image Processing Open RAW file in RAW processor (Camera RAW, Lightroom) RAW Data Color Filter Array Interpolation - RGB Neutral White Balance Camera Profile; srgb, A-RGB, ProPhoto Gamma Correction Exposure Correction Set White Point Exposure Correction Set Black Point Tone Corrections Sharpening / Noise Reduction Lens Correction Vignetting/ Aberrations A RAW processor will perform the first four steps for you, up through Exposure Correction. RAW data looks very dark and without the processors automatic configuration it wouldn t be viewable. RAW files are then saved; DNG / TIFF / PNG or other file formats. This diagram does not take artist manipulation into account

16 Chapter Three B&W One Channel Capture Pixel Defect Correction Photo Response Non-Uniformity RAW Data Image Processing Pipeline Original capture of an image will be in black and white. A sensor has no way of capturing color except through the filter array process. Original image is dark and unviewable. There is a possibility that an image will have a number of defective pixels caused by manufacturing faults or operation conditions where some pixels will respond to light differently than surrounding pixels. This step finds those defects and averages out neighboring pixels to determine the appropriate value of the missing pixel. Manufacturing processes are rarely perfect and often there are slight variations across the surface of a sensor that can result in sensitivity differences with pixels. This step corrects for this sensitivity shift. RAW data is black and white and naturally dark. RAW processors will perform the calculations for Color Filter Array, Neutral White Balance, Camera Profile and Gamma Correction just like the camera will do with JPEG compression. Using a RAW processor, like Camera RAW or Lightroom, will give more artistic freedom when manipulating photographs. Color Filter Array Interpolation - RGB Neutral White Balance Camera Profile; srgb, A-RGB, ProPhoto Gamma Correction Exposure Correction Set White Point and Black Point Color Filter Array Interpolation takes the information from the RAW data produced by the Bayer pattern and formulates three color channels. Combining these three channels produces a full color image. See page 26. A camera will do a certain degree of white balance and this is usually altered within manipulation. This step is also usually operator preference since it can be set on most cameras. Camera Profile will determine the amount of color correction that is needed. This will also directly influence the amount of color that is captured. srgb is used for web while the bigger gamut of A-RGB or ProPhoto is better for printing. Gamma Correction is needed due to the dark image of the original capture. Without Gamma Correction the image would be unviewable. Exposure Correction goes in unison with Gamma Correction for it allows the image output to be closely replicating the original scene. Setting white point and black point is necessary in accomplishing the greatest amount of Dynamic Range possible. This is also subjective and can be manipulated for artist effect. Image Processing Pipeline Image Processing Pipeline B&W One Channel Capture Pixel Defect Correction Photo Response Non-Uniformity RAW Data Color Filter Array Interpolation - RGB Neutral White Balance Camera Profile; srgb, A-RGB, ProPhoto Gamma Correction Exposure Correction Set White Point Exposure Correction Set Black Point 30 31

17 Chapter Three Tone Corrections Sharpening / Noise Reduction Lens Correction Vignetting / Aberrations Output Image Processing Pipeline Remaps wide pixel values to a range that a display is capable of viewing. Noise can be produced by many things, including the sensor (shot noise), ADC (readout noise), or weak signals (snow). The most common techniques for noise reduction are image averaging, which improves the signal to noise ratio, and median filtering, which replaces pixels by the median value of the pixel and that pixels neighbors. Corrects lens distortion whether it be from barrel distortion (where lines bow outward from the center of an images) or pincushion distortion (where lines bow inwards from the center of an image). Most camera lens suffer from some degree of distortion. Output is represented by a print, viewing on a monitor (Internet, ipad, etc.), or archiving of the processed image. Different output applications will result in different processing in regards to resolution and image size. Certain decisions have to be made on a case by case basis. Spectral Power Distribution Light Source Characteristics MACBETH Color Checker Human Eye Characteristics Standard Human Observer Camera Profile srgb, A-RGB, ProPhoto This is pre-determined by analyzing the power of the light at each wavelength in the visual spectrum. The result contains all the basic physical light data and serves as a starting point for analysis of color. Most cameras come preset with options, which is under whitebalance. These presets are usually characterized by the specific setting that the photograph is being captured. Flash, Sunny, Tungsten, shade, etc. are a few of the presets. Custom white balance is also available for a more precise calculation. The MACBETH color checker is often used for a more precise color calculation, which is done after capture and then processed through its native software. This color profile can then be applied to other images under the same lighting conditions. Experiments were conducted to calculate the ability of the human eye to perceive color. This was done across the entire visual spectrum and the results determined the color sensitivity of the average human. The above three steps in the imaging pipeline are combined to calculate a correct color profile that then can be applied to images. The RAW data pipeline will give you more creative control over this process when editing in a RAW processor. srgb, A-RGB and ProPhoto are separate camera settings that will allow more or less color capture. srgb being the smallest and ProPhoto being the largest. Image Processing Pipeline Image Processing Pipeline Stored as JPEG with in-camera processing. Stored as.tiff,.dng,.png, etc. with RAW processing. Images then archived Creates a Color Correction Profile. Used in both JPEG and RAW pipelines. Tone Corrections Sharpening / Noise Reduction Lens Correction Vignetting/ Aberrations Output Spectral Power Distribution Light Source Characteristics MACBETH Color Checker Human Eye Characteristics Standard Human Observer Camera Profile; srgb, A-RGB, ProPhoto

18 Chapter Four Chapter Four Digital Output Digital Output Printer Technologies Monitor Display Technologies Halftoning DPI & PPI Digital output consists of the final outcome that is desired by the artist or demanded by the client. The rapid ascent of digital technology is altering the output process and forcing artists to capture images that will be viewed on digital monitors but also to understand the printing process for continuous replication. Understanding both processes is vital to match monitor display and print quality. 35

19 Chapter Four Printer Technologies There are two categories of printing, which are desktop and commercial based. Desktop printers are by nature slower but will give more control over each print. Commercial based printers are reliant on speed and producing a high quantity of prints. Inkjet, Laser, and Dye-sublimation, are the types of processes that are used in todays modern photo printers. Continuous Ink Jet is used commercially for marking and coding of products and packages. Liquid ink is directed by a highpressure pump from a reservoir through a microscopic nozzle, which creates a continuous stream of ink droplets. A crystal is used to break up the droplets at regular intervals. A charging electrode creates an electrostatic field, which is varied according to the degree of drop deflection desired. Continuous Ink Jetprintheads that are characterized by three processes: (1) continuous pressurized drop generation, (2) modulation by drop deflection, (3) ink recirculation. Digital Output Inkjet Printers- Printing process that operates by propelling tiny droplets of ink onto paper. Thermal Ink Jet- Incorporates a heater located in the floor of an ink channel near the exit nozzle. A liquid-to-vapor-transition results in a volume expansion of the heated liquid. Piezoelectric Ink Jet- Uses Piezoelectric crystals to deposit materials directly on substrates. Inkjet printers are the most common type of computer printing for the general consumer. Inkjet is low cost, high quality, and ease of use. The operating process used by Inkjet printers is to propel tiny droplets of liquid ink onto paper. There are different types of Inkjet printing used to distribute the ink across the paper. These types can be classified into three categories; Thermal Ink Jet, Piezoelectric Ink Jet, Continuous Ink Jet. Thermal Ink Jet works by having a print cartridge with a series of tiny electrically heated chambers. A pulse of current through the heating elements forms a bubble, which propels a drop of ink onto the paper. This is the process of most consumer based ink jet printers. This is not the same as Thermal Transfer. Piezoelectric Ink Jet applies the same principle as thermal ink jet but doesn t use the heating element. When voltage is applied, the crystal (piezoelectric material) changes shape or size, this generates pressure in the fluid forcing a drop of ink out of the nozzle. Most commercial and industrial ink jet printers use this process and are more expensive. Laser Printers produce high quality text and graphics on plain paper. These printers use an electrically charged, light sensitive metal drum that is exposed by a laser in the regions corresponding to image areas. This forms an image out of many microscopic dots. The exposed areas become oppositely charged and will accept oppositely charged particles of toner. The toner adheres to the drum in the areas exposed by the laser and is then transferred to the paper passing beneath it. Heat and pressure are then applied to keep the toner from rubbing off. Dye-sublimation is a process that uses heat to transfer dye onto a medium; paper, fabric, plastic, etc. The dye transitions between solid and gas state without going through a liquid stage. This technology allows for continuous tone printing as well as dry prints. Dye-sub coats the paper with one color and then winds the ribbon to the next color to prepare for the second cycle. This is done 4 times, which accounts for three colors (Cyan, Magenta, Yellow) and one clear overcoating to protect the paper from discoloration due to UV light, air, as well as warm conditions. This coating also renders the paper water resistant. Laser Printers- A printer linked to a computer producing good-quality printed material by using a laser to form a pattern of electrostatically charged dots on a light-sensitive drum, which attract toner (or dry ink powder). The toner is transferred to a piece of paper and fixed by a heating process Dye-Sublimation- A printing process using small heating elements to evaporate pigments from a carrier film, depositing these smoothly onto a substrate

20 Chapter Four Monitor Display Technologies Digital Output LCD- Liquid Crystal Display, an electronic visual display in which the application of an electric current to a liquid crystal layer makes it opaque. Modern technology is rapidly changing the output industry. Printing is shifting to a more monitor display medium. Smartphones and handheld tablets are becoming a larger part of our output industry and causing the traditional print technologies to become decreasingly sought after. The three widely used display technologies are liquid crystal display (LCD), plasma display panel (PDP), and organic light-emitting diode (OLED). LCDs are used in a wide range of applications from televisions to aircraft cockpit displays and are common in consumer devices such as clocks, watches, calculators, and gaming devices. Each pixel of an LCD display consists of a layer of molecules aligned between two transparent electrodes and two polarizing filters. Liquid crystals are positioned between the polarizing filters, which block light or allow light to pass. The liquid crystals do not produce light directly and have to rely on natural incoming light or a backlight. OLEDs are used across most display mediums. These mediums range from television screens, computer monitors, and portable systems such as mobile phones and personal digital assistants (PDAs). OLEDs consist of a layer of organic materials situated between two electrodes, the anode and cathode. An electrical current causes the electrodes to emit light, which allows the device to work without a backlight. The absence of this backlight allows an OLED to be thinner and lighter. Liquid Crystal Display Pros No geometric distortion Usually no refresh rate flicker Razor sharp images Can be made in any size or shape No theoretical resolution limit OLED- Organic light-emitting diode, a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compounds which emits light in response to an electric current. Cons Limited viewing angle Black levels may appear bright Smearing and ghosting artifacts Fixed bit depth Input Lag PDP- Plasma Display Panel, a display made from pixels that have been illuminated by either plasma or a gas charge. PDPs are common in large television displays over 30 inches. This technology utilizes small cells containing electrically charged ionized gases, referred to as fluorescent lamps. Plasma displays are typically brighter, have a larger color gamut and have a darker black level compared to LCDs. Plasma Display Panel Organic Light-Emitting Diode High contrast ratios Millisecond response time Excellent viewing angle Zero color, saturation, brightness distortion Variable power consumption Very high contrast Excellent viewing angle Very light weight Excellent black level Wide gamut and vivid colors Large pixel pitch Some image flicker Can suffer image burn-in Relatively fragile Defective pixels may occur Can suffer screen burn-in Poor readability in bright light Prone to water damage Presently expensive to manufacture Organic materials can decay over time 38 39

21 Chapter Four Halftoning- A picture in which the gradations of light are obtained by the relative darkness and density of tiny dots produced by photographing the subject through a fine screen. Halftoning Halftoning is a process of projecting a continuous tone image through a halftone screen to break the image into a number of dots. Darker areas make a larger shadow and therefor a larger dot is utilized. DPI & PPI Dots per inch (DPI) refers to the measure of spatial printing, the number of dots that can be placed within the span of one inch. A dot is the smallest binary element that a device can generate. Dots per inch- The number of individual dots that can be placed in a line within the span of 1 inch. Digital Output Pixels per inch (PPI) refers to the measure of the resolution of devices in context such as computer displays, image scanners, and digital camera image sensors. Pixels per Inch- The number of pixels in an image that occur in one line along one inch. Ppi is the same as lpi. Moiré effect- The effect of superimposing a repetitive design, such as a grid, on the same or a different design in order to produce a pattern distinct from its components. Color Halftoning is the same process but is repeated through each color channel (CMYK). A varying degree of each color channel will result in a solid color as demonstrated in the image shown here. There are also different dot shapes that when used simultaneously will eliminate the moiré effect. Round dots are the most commonly used and suitable for light images and skin tones. Elliptical dots are appropriate for images with many objects and square dots are best for detailed images. Square dots are not recommended for skin tones. It is common to refer to ppi as dpi but is incorrect. To determine which one to use in certain situations you can ask yourself if a device is capable of handling multiple gray levels and if it is then it should be assumed that dpi really means ppi. Pixels are capable of capturing multiple gray levels within the pixel (scanner, etc.) and dots are capable of different gray levels by placing them closer together or farther apart, which means that each dot cannot handle multiple gray levels. Converting ppi into dpi and vice versa is quite simple and needs to be understood in order to maintain crisp and clear images when printing. An image is captured in ppi and, at times, printed as dpi. The rule of 16 is applied to transition between dpi and ppi. The generic formula for converting dots to pixels is dpi/16. The opposite also applies when converting from pixels to dots, ppi X 16. Rule of 16- Equation for converting dpi into ppi Posterization- Of an image entails conversion of a continuous gradation of tone to several regions of fewer tones, with abrupt changes from one tone to another. The resolution of a halftone screen is measured in lines per inch (lpi). This refers to the number of lines of dots within one inch. This is dependent on the printing application and the file resolution must match the output resolution or there will be posterization

22 Diagram References Applications of Electrostatics. (July 5, 2012). In Connexions. Retrieved November 4, 2012, from content/m42329/latest/. Bradley, R., & Gryffenberg, J. (March 5, 2010). What is Dye Sublimation?. In TogBlog gazette. Retrieved November 4, 2012, from Coursaris, C. (1999). Liquid Crystal Technology. In TC201 Web Tutorial. Retrieved November 6, 2012, from Credner, T. (1999). Astronomical Image Processing with Preserved Colors. In Preserving Colors in Color Composites. Retrieved September 4, 2012, from html. Design, Thyon. (June 14, 2010). Gamut: Let s get Techni-Colour. In Thyon Design Blog. Retrieved October 4, 2012, from Inkjet. (2012). In DP3, Digital Print Preservation Portal. Retrieved November 4, 2012, from dp3project.org/technologies/digital-printing/inkjet. Omo, J. (November 1, 2010). Color Space, Escape the Ordinary World. In Around Hawaii: Oceanic Time Warner Cable s Community Website. Retrieved October 4, 2012, from com/lifestyle/art_and_leisure/ color-. Ottawa s Plasma TV Store. (1999). In Stereo Plus & Design. Retrieved November 6, 2012, from spodesign.com/products/video/plasmatv.php. Ozil, Riana. (November 2, 2010). Printer or Printer. In Welcome to My Blog. Retrieved November 4, 2012, from Ravi. (April, 2009). Micro-Inkjet Printer Head. In Ravi s Blog. Retrieved November 4, 2012, from nanoravi.wordpress.com/2010/07/25/inkjet-printer-head/. Book Created for Imaging Systems Minor Rochester Institute of Technology Professor: Nitin Sampat All Images 2012 Ira Morris IraMorrisPhotographer.com 42

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