“Develop success from failures. Discouragement and failure are two of the surest stepping stones to success.”
UNIT – 4
DEFINITION OF COLOUR
Color is an optical phenomenon, a sensory impression conveyed by the eye and the brain. Color is not a physical variable; accordingly it has no physical unit .An object is not colored per se, but the sensation of color is produced as a result of irradiation by light. Sunlight, which appears to be white, radiates onto an object and is partially reflected. Consequently an object that reflects the red area of the visible spectrum appears colored. An object that reflects completely in the entire visible spectrum usually appears to be white and a completely absorbent body appears to be black.
A color measuring instrument (colorimeter, spectrophotometer) primarily measures only the chromatic stimulus, from which the color stimulus specification and possibly also the color perception can then be deduced numerically by means of suitable interpretation models. These may, for example, be the standard color spaces defined by the CIE: CIELAB, and CIELUV.
What is a color management system? and its needs
A system that transforms data encoded for one device (such as scanner RGB) into that for
another device (such as printer CMYK) in such a way that it reproduces on print the same colours as
those scanned. Where exact colour matching is not possible the result should be a pleasing
approximation to the original colours. In general the term colour management system is usually
reserved for those systems that use the internationally accepted CIE system of colour measurement
as a reference.
Color terminology
What is the definition of a color?
Colour is the sensation produced in response to selective absorption of wavelengths from visible light. It possesses the attributes of Brightness, Colorfulness and Hue. An international standard developed by CIE can be used for measurement of these attributes for any colour.
CIE Chromaticity Diagram
The CIE color diagram contains all colors. The colors described in the CIE system is plotted on a chromaticity diagram. The diagram is the horse shoe shaped “spectrum locus” (the line connecting the points representing the chromaticities of the spectrum colors). The two dimensional map of color obtained is known as Chromaticity diagram. The wavelengths of the visible spectrum are plotted on the outside. The x and y axes designate two of the three standard color value ratios in relation to the eye of a standard observer. Only a certain number of the colors that occur in nature can be reproduced in printing using the four process colors of CMYK. The colors produced in four color offset are within the polygon. Compare also the color spectrum of a positive slide and the spectrum used in newspaper printing. The vertical from the achromatic center of the color triangle represents the luminance axis ‘capital Y’. if the luminance axis is also plotted, we talk about the CIE color space.
Spectral Reflectance curves
UCR an GCR
Color Management system: Color management is the process of ensuring consistent and accurate colors across various devices, such as monitors, printers, and cameras. It involves the use of color profiles, which are standardized descriptions of how colors should be displayed or reproduced.
Color management is necessary because different devices have different color capabilities and characteristics. For example, a monitor may display colors differently than a printer can reproduce them. Without color management, the same image may appear differently on different devices, leading to inconsistencies and inaccuracies.
To achieve color management, a color profile is created for each device involved in the color workflow. This profile describes the device's color capabilities and characteristics, such as its color gamut (range of colors it can display or reproduce) and color temperature. These profiles are then used to translate colors between devices, ensuring consistent and accurate color reproduction.
Color management is particularly important in industries such as graphic design, photography, and printing, where accurate color representation is crucial. It helps to maintain color consistency throughout the entire workflow, from capturing an image to displaying or printing it.
Parts of color management are implemented in the operating system (OS), helper libraries, the application, and devices. The type of color profile that is typically used is called an ICC profile. A cross-platform view of color management is the use of an ICC-compatible color management system. The International Color Consortium (ICC) is an industry consortium that has defined:
There are other approaches to color management besides using ICC profiles. This is partly due to history and partly because of other needs than the ICC standard covers. The film and broadcasting industries make use of some of the same concepts, but they frequently rely on more limited boutique solutions. The film industry, for instance, often uses 3D LUTs (lookup table) to represent a complete color transformation for a specific RGB encoding.
At the consumer level, system wide color management is available in most of Apple's products (macOS, iOS, iPadOS, watchOS). Microsoft Windows lacks system wide color management and virtually all applications do not employ color management. Windows' media player API is not color space aware, and if applications want to color manage videos manually, they have to incur significant performance and power consumption penalties. Android supports system wide color management, but most devices ship with color management disabled.
Caliberation: In conventional photography, from capturing an image on a color negative to getting a color print back from a photofinisher, most consumers do not have to bother with measuring light and color because the entire image chain (from film to reflection print) has been designed to reproduce good tone and color, and the uncontrolled variables left are taken care of by the automatic focus and exposure algorithms in the camera, and automatic color–density balance algorithms in the photofinishing printer. The conventional photographic system is a closed system and no user intervention is required. In electronic imaging, the situation is quite different. Digital cameras, film scanners, paper scanners, color monitors, and color printers are not manufactured to the same system specifications. Therefore, these imaging devices require careful calibration to ensure that they work together to reproduce good color images. Figure 16.1 shows a general block diagram for a color imaging application. The image data from an input device have to be calibrated so that they can be manipulated and processed according to the algorithm specifications. Similarly, the image processing algorithm outputs a digital image in a chosen color metric and that image has to be converted through an output calibration so that the desired color image can be reproduced by the output device.
Let us say, we have a nice color picture (reflection print) of our relatives and friends, and wewould like to produce more copies of the picture to send to each of them. We use a scanner to digitize the picture into a digital file which is then sent to a color printer for printing.
Calibration is like characterization, except that it can include the adjustment of the device, as opposed to just the measurement of the device. Color management is sometimes sidestepped by calibrating devices to a common standard color space such as sRGB; when such calibration is done well enough, no color translations are needed to get all devices to handle colors consistently. This avoidance of the complexity of color management was one of the goals in the development of sRGB.
Embedding: Image formats themselves (such as TIFF, JPEG, PNG, EPS, PDF, and SVG) may contain embedded color profiles but are not required to do so by the image format. The International Color Consortium standard was created to bring various developers and manufacturers together. The ICC standard permits the exchange of output device characteristics and color spaces in the form of metadata. This allows the embedding of color profiles into images as well as storing them in a database or a profile directory.
Color Transformation:
Color transformation, or color space conversion, is the transformation of the representation of a color from one color space to another. This calculation is required whenever data is exchanged inside a color-managed chain and carried out by a Color Matching Module. Transforming profiled color information to different output devices is achieved by referencing the profile data into a standard color space. It makes it easier to convert colors from one device to a selected standard color space and from that to the colors of another device. By ensuring that the reference color space covers the many possible colors that humans can see, this concept allows one to exchange colors between many different color output devices. Color transformations can be represented by two profiles (source profile and target profile) or by a devicelink profile. In this process there are approximations involved which make sure that the image keeps its important color qualities and also gives an opportunity to control on how the colors are being changed.
Profile connection space: In the terminology of the International Color Consortium, a translation between two color spaces can go through a profile connection space (PCS): Color Space 1 → PCS (CIELAB or CIEXYZ) → Color space 2; conversions into and out of the PCS are each specified by a profile.
Gamut Mapping: In nearly every translation process, we have to deal with the fact that the color gamut of different devices vary in range which makes an accurate reproduction impossible. They therefore need some rearrangement near the borders of the gamut. Some colors must be shifted to the inside of the gamut, as they otherwise cannot be represented on the output device and would simply be clipped. This so-called gamut mismatch occurs for example, when we translate from the RGB color space with a wider gamut into the CMYK color space with a narrower gamut range. In this example, the dark highly saturated purplish-blue color of a typical computer monitor's "blue" primary is impossible to print on paper with a typical CMYK printer. The nearest approximation within the printer's gamut will be much less saturated. Conversely, an inkjet printer's "cyan" primary, a saturated mid-brightness blue, is outside the gamut of a typical computer monitor. The color management system can utilize various methods to achieve desired results and give experienced users control of the gamut mapping behavior.
Rendering Intent: When the gamut of source color space exceeds that of the destination, saturated colors are liable to become clipped (inaccurately represented), or more formally burned. The color management module can deal with this problem in several ways. The ICC specification includes four different rendering intents, listed below. Before the actual rendering intent is carried out, one can temporarily simulate the rendering by soft proofing It is a useful tool as it predicts the outcome of the colors and is available as an application in many color management systems:
Absolute colorimetric
Absolute colorimetry and relative colorimetry actually use the same table but differ in the adjustment for the white point media. If the output device has a much larger gamut than the source profile, i.e., all the colors in the source can be represented in the output, using the absolute colorimetry rendering intent would ideally (ignoring noise, precision, etc.) give an exact output of the specified CIELAB values. Perceptually, the colors may appear incorrect, but instrument measurements of the resulting output would match the source. Colors outside of the proof print system's possible color are mapped to the boundary of the color gamut.
Absolute colorimetry is useful to get an exact specified color (e.g., IBM blue), or to quantify the accuracy of mapping methods.
Relative colorimetric
The goal in relative colorimetry is to be truthful to the specified color, with only a correction for the media. Relative colorimetry is useful in proofing applications, since it can be used to get an idea of how a print on one device will appear on a different device. Media differences are the only thing that one really should adjust for, although some gamut mapping also needs to be applied. Usually this is done in a way where hue and lightness are maintained at the cost of reduced saturation. By default, in-gamut colors are unchanged, while out-of-gamut colors are clamped.
Relative colorimetric is the default rendering intent on many systems.
Perceptual
The perceptual intent smoothly moves out-of-gamut colors into gamut, preserving gradations, but distorts in-gamut colors in the process. Like the saturation intent, the results really depend upon the profile maker. This is even how some of the competitors in this market differentiate themselves. The profile maker tries to make results pleasing on this intent. Perceptual rendering is recommended for color separation.
Saturation
The saturation intent is designed to present eye-catching business graphics by preserving the saturation (colorfulness). It is most useful in charts and diagrams, where there is a discrete palette of colors that the designer wants saturated to make them intense, but where specific hue is less important.
In practice, photographers almost always use relative or perceptual intent, as for natural images, absolute causes color cast, while saturation produces unnatural colors. If an entire image is in-gamut, relative is perfect, but when there are out of gamut colors, which is preferable depends on a case-by-case basis. CMMs may offer options for BPC and partial chromatic adaptation.
A black point correction (BPC) is not applied for absolute colorimetric or devicelink profiles. For ICCv4, it is always applied to the perceptual intent. ICCv2 sRGB profiles differ among each other in a number of ways, one of which being whether BPC is applied.
Implementation:
Color management module: Color matching module (also -method or -system) is a software algorithm that adjusts the numerical values that get sent to or received from different devices so that the perceived color they produce remains consistent. The key issue here is how to deal with a color that cannot be reproduced on a certain device in order to show it through a different device as if it were visually the same color, just as when the reproducible color range between color transparencies and printed matters are different. There is no common method for this process, and the performance depends on the capability of each color matching method.
Some well known CMMs are ColorSync, Adobe CMM, Little CMS, and ArgyllCMS.
Closed loop colour: Closed-loop color can mean something different to different audiences. When I first think about closed-loop color control, I may think about the pressroom, where it is really just a question of integrating measurements directly from the press, adjusting them, measuring and reporting, offering a nice closed-loop system that adjusts, controls, and allows me to report the results. But that’s really only one small aspect. You can incorporate a loop from the ink room, for instance, and bring that information directly into the pressroom as well. Or you can even start sooner and close the loop from the designer or the brand owner.
So, closed-loop color control essentially closes the loop in communication between users. By introducing CxF, X-Rite provided a way to close the loop in communication anywhere in the process.
I am very interested in quality control because I used to produce work. I know that without good checks and balances, you end up creating more waste, which ultimately means you lose money. No matter where you’re implementing it – whether just the actual linearization of your plates or your digital printer, or before that for analog printing – quality control means you’re checking the incoming quality of your supplies, sometimes even before they're delivered to the pressroom.
There’s not a question of quality or whether it’s meeting specification, because a lot of the work that we do today, particularly in the printing industry, is driven by specifications. And those specifications are designed around delivering quality – quality to a number that is established by making sure you have the right paper, and that your ink, whether it’s delivered premixed or mixed in house, is meeting the standard. Without that quality control check, you may produce something that you think is right, but end up delivering the wrong product.
One of the reasons to look at the ink room as a total solution for print is because almost everything passes through the ink room. You need good tools to control the quality of both the incoming supplies and the final output. You also need a good formulation package so you can confidently formulate inks that will meet your requirements. If an ink needs to meet a requirement under different lighting conditions, you can't just test for a single lighting condition. You need to find out whether this ink will create the right match under both store light and home viewing.
X-Rite offers a host of solutions to help you achieve color quality. One of the areas I don’t think we’re as well known for as we should be is the Pantone Certified Printer program. It's a certification program where we look at how the printer is implementing ISO standards all the way through the workflow and whether they can reproduce Pantone Colors correctly. It offers more than a lot of other programs because it considers printing standards, X-Rite’s know-how in Pantone, and the ability of our trainers to walk through every step of the process to provide a really good picture of how to improve the workflow. Pantone Certified Printers give confidence to people who want to buy their work because they have the whole ballgame wrapped up.
We also offer other tools to contribute to the program. From a measurement side we offer the big i1Pro 3 Family for prepress. It’s probably the most well-known product in that whole space. On the printing side we have the eXact series and the eXact Scan, as well as IntelliTrax 2 Pro, which is the fully automated pressroom solution. The eXact and IntelliTrax2 also connect up with our ColorCert quality control and reporting solution. We even have the right lighting solution, whether you’re in the industrial side of the business, or you’re in the printing business.
We can help with any part of the workflow. If you’re a designer picking a color, we offer tools and solutions to specify both physical and digital Pantone Standards and associate them use throughout the workflow. The same thing goes for the brand side. PantoneLIVE allows you to select a color for use throughout the entire workflow with assurance that no matter where it’s being output, the end solution will give the right color and the right quality.
In a traditional photo-to-print workflow, color must travel through different devices – including digital cameras, displays, design programs, printers – leaving many opportunities for color variations. Even when using the best quality devices, color consistency of the specified color can shift if all devices don’t speak the same language. A color management system ensures each particular device can capture and display color correctly so photographers, designers, and printers can work quickly and with confidence.
An ICC color management system uses hardware and software to calibrate and create a color profile for input devices (cameras), display devices (monitors), and different output devices (printers) so they are optimized to transfer color data. The resulting ICC profile includes color settings and data that characterize the behaviors of the color management system, including the input, display, and output devices, to translate color for more control over color reproduction. ICC color space characteristics for icc profiles are defined and managed by the International Color Consortium.
Incorrect color can lead to poor editing decisions for photographers and designers and expensive rework for printers. Even with top-of-the-line equipment, color can go wrong if each device is not calibrated and profiled. Color management ensures that the colors captured by the camera are the same colors that will preview on the monitor for design editing (also called soft-proofing), and the same colors that will print using any printing process. Color management essentially removes the guesswork from color control.
Each device used to capture and create digital images uses slightly different CMYK or RGB formulas to create the same color. A source device like a digital camera, scanner and display use the additive color model, rely on different gamuts, and vary between manufacturers. Printers can be RGB or CMYK and use a variety of different inks and papers. Applications like Adobe Photoshop or InDesign used to prep images and files must also be set up to handle color management. Mixing these color characteristics can lead to surprises in final output.
A color-managed workflow helps all devices speak the same color language so they can share accurate color information. There are four key steps in setting up a color-managed workflow, which we call the four Cs of color management.
Posted August 23, 2023 by Mark Gundlach
Working in prepress holds a unique challenge. Even if your color workflow is tight, everything can fall apart if the customer’s file isn’t color managed.
We’ve all seen it. You receive a file that the customer claims is ready to print, yet when you open it on your computer, the colors don’t look right at all. You can’t send it to print without knowing for sure, because you’re the one who will take the hit for wasted time and materials if it’s wrong.
Knowing how color management for print and packaging works from beginning to end will help you better understand your role in the process and arm you with the knowledge to educate your clients so that future files received reflect the correct color intent.
The goal of color management is to match color appearance as closely as possible from input to output and between devices. These images demonstrate a workflow without color management (above) and with it (below).
A color-managed workflow will help all of your devices speak the same color language so they can share accurate color information.
Each device you use to capture and create digital images uses slightly different CMYK or RGB formulas to create the same color. Digital cameras, scanners and displays use the additive color model, rely on different gamuts, and vary between manufacturers. Printers can be RGB or CMYK and use a variety of different inks and papers. When you’re using an application like Adobe® Photoshop® or InDesign® to prep images and files, you need to set them up to handle color management, too.
There are four key steps in setting up a color-managed workflow, which we call the four Cs of color management.
First, you must ensure your devices are capable of producing consistent colors. If your monitor’s color is brighter on the left side than the right, or your proofing printer can’t produce consistent color from start to finish, then there’s not much color management can do to help. You need a new one.
Once you know your device is capable of reproducing consistent color, you need to bring it back into specification. Device color will drift over time, and calibration re-adjusts everything to achieve the best possible gamut.
Calibrating a monitor with X-Rite’s i1Pro 2 spectrophotometer.
Next, you should use a color measurement instrument, such as a colorimeter or spectrophotometer, to determine the device’s color reproduction characteristics. Even identical devices built on the same day from the same manufacturer will have slight variations in color. Characterization will optimize the settings for the best image reproduction on that particular device.
When characterizing a monitor, software flashes a series of known RGB values on screen, and the color measurement device measures them. To characterize a printer, print a test chart with anywhere from a few to thousands of color samples and measure them with the color measurement device.
Measuring a test chart to profile a printer with X-Rite’s i1Pro 2.
The collected color data is compared with sample colors and used to create an ICC profile, which is basically a three-dimensional map, or color space, of all of the colors the device can capture, display or print. It describes the specific characteristics of the device so that other devices know which color language it is speaking.
Conversion is the process of moving color data from the color space of one device to the color space of another. These controlled conversions take place in a working space. Think of it like an airline hub – a common place to connect workflows.
If an image is captured by an RGB camera, edited in Photoshop, added to a layout in InDesign, then printed on a CMYK printer, it must be converted multiple times. Embedded profiles help retain color appearance as the image moves between working spaces. It’s like wearing a nametag at a meeting. If the image takes its color reproduction characteristics with it, other devices know exactly what it is about so your workflow can produce consistent color.
Embedded profiles help multiple devices speak the same color language. The conversion between devices happens in a working space.
Back to our customer file. Before you launch your editing tools to fix the bad color, there are some things you need to do.
Make sure your monitor is calibrated and profiled to display accurate color so you know you’re seeing a true representation of what’s in that digital file. This is called “soft proofing” and is a very important part of a color-managed workflow. Soft proofing requires a good quality display and a monitor profile that can display the image at the correct color temperature and gamma settings.
If your monitor is set up for soft proofing, the problem isn’t on your end. It’s time to give your customer a call.
If not, make sure he is also working on a calibrated and profiled monitor. (Here’s your chance to provide some education that will save them time and money in the future!) If your customer’s monitor IS set up for soft proofing, compare your ICC profile color settings. You both need to be using the same settings to see accurate colors.
If you and the customer both see the same color casts, the problem most likely occurred when the photo was captured, or during layout design. If the file itself is incorrect, a calibrated display can’t fix it.
Regardless of the cause, the file must be corrected. Ask the customer if they want your department to make the corrections or hand that task back to them. If the customer chooses to make the corrections himself, it is another learning opportunity that likely will contribute to better files in the future. Asking this question will also offer some degree of protection… if the customer asks you to run the file as is, they can’t object to the results when they see the printed piece.
PS color separation: This article pertains to ArcGIS versions 8.x and 9.x only. Later versions of ArcGIS may contain different functionality, as well as different names and locations for menus, commands and geoprocessing tools.
Note:
It is highly recommended to use ArcGIS Pro for printing and exporting, especially when experiencing issues caused by the limitations of the ArcMap display engine. More specifically, ArcGIS Pro is not restricted by the graphical device interface (GDI) limitations that some users experience in ArcMap. For example, transparency is natively supported in ArcGIS Pro, preventing the rasterization of layers. Additionally, ArcGIS Pro supports transparency in layout elements
For ArcMap 8.x:
PostScript separates can not be created nor printed with the PostScript printer engine if the printer driver is not enabled with PostScript.
If intending to print on a printer or imaging device that is not in-house, install a local test printer to duplicate the settings of the target printer. See: How To: Create a test printer and set it to be the default printer for Windows
Creating a PostScript Level 3-compatible separates file will write all four-color separates into a single PostScript file, which may not be compatible with some printers or imaging devices. Be sure to check the manufacturer's documentation before selecting this option.
The screen angles will default with the value found in the PPD file. Be sure to test any modifications you make, as they may drastically change the look of your output image.
ArcMap does not support setting SPOT plate, which is why the SPOT plate saturation percentage is unavailable.
The CIE system
In 1861 Clerk Maxwell (1890) studied ways of representing the additive primaries, red, green and blue, graphically so that a quantitative descrip- tion of colour could be obtained. He arranged the primaries at the three points of an equilateral triangle.
If we refer to the colour diagram of the additive primaries (Fig. 3.5), it can be seen that equal parts of blue and green produce a blue-green colour called cyan. This can be represented on Maxwell's triangle at a point midway between the blue and green points. Similarly red and green produce yellow; red and blue produce magenta. Addition of all three primaries gives white which Maxwell put in the centre of the triangle (Fig. 3.7). If we start at the middle and move along a line to the blue point, we pass from white through increasingly saturated blues to the completely saturated blue primary. Similar lines can be drawn from the white point to the green and red primaries.
If now we carry out a similar exercise with the intermediate colours, cyan, yellow and magenta, we find that point C on the triangle, while being correct for hue, is not a completely saturated cyan. It is possible to produce a more saturated cyan light than that made by adding green and blue lights, since these are not ideal primaries. The saturated cyan will be at a point C1 outside the triangle. This presents problems if we wish to quantify the colour. The desaturated cyan at point C can be described in terms of positive amounts of blue and green, say y parts of green and z parts of blue, but since the saturated cyan C1 is outside the triangle we can only describe it by introducing a third quantity. This lies on the line from
The red point through the centre, but since it is beyond the centre white point the values will be negative. We then have to describe the point Ci on this diagram as being made up of y parts of green, z parts of blue and minus x parts of red, i.e.
C1 = yG+zB XR
If now all the saturated colours are plotted, they will be found to lie outside the triangle, but touching the red, green and blue points. This line is known as the spectrum locus (Fig. 3.8).
To avoid negative quantities in our description of a colour, the locus can be enclosed in a triangle X, Y, Z (Fig. 3.9).
In such a diagram the points X, Y, and Z represent colours which are more saturated than actual colours, they are therefore unobtainable with any light source and are described as imaginary primaries (McLaren, 1983, pp. 96-102). X is a reddish purple of a higher saturation than a real colour, Y has a saturation higher than any green and Z higher than any blue. Using this system we can deline a colour by measuring it with an instrument and obtaining values for X, Y, and Z. These values can be represented as ratios:
x =
X____
X+Y+Z
y =
Y_____
z =
Z____
Then x+y+z = 1.
It is therefore only necessary to use two of these values, known as chromaticity co-ordinates, to define the hue. The values can then be plotted on ordinary graph paper.
This description of a colour does not take luminance or brightness into account. Two colors can have the same x and y values, therefore the same hue, but differ in luminance. To quantity luminance it was decided to define the X and Z stimuli mathematically in such a way that they have zero luminance, while the value of Y, deliberately chosen to equal the response curve of the eye, gives the luminance information.
This system was adopted by the commission international de I’Eclairage (CIE) in 1931. A full explanation is given by McLaren (1983, pp.102-107.)
Tone mapping/Tone compression
Tone mapping is a technique used in image processing and computer graphics to map one set of colors to another to approximate the appearance of high-dynamic-range (HDR) images in a medium that has a more limited dynamic range. Print-outs, CRT or LCD monitors, and projectors all have a limited dynamic range that is inadequate to reproduce the full range of light intensities present in natural scenes. Tone mapping addresses the problem of strong contrast reduction from the scene radiance to the displayable range while preserving the image details and color appearance important to appreciate the original scene content.
Forms of tone mapping long precede digital photography. The manipulation of film and development process to render high contrast scenes, especially those shot in bright sunlight, on printing paper with a relatively low dynamic range, is effectively a form of tone mapping, although it is not usually called that. Local adjustment of tonality in film processing is primarily done via dodging and burning, and is particularly advocated by and associated with Ansel Adams, as described in his book The Print; see also his Zone System.
The normal process of exposure compensation, brightening shadows and altering contrast applied globally to digital images as part of a professional or serious amateur workflow is also a form of tone mapping.
However, HDR tone mapping, usually using local operators, has become increasingly popular amongst digital photographers as a post-processing technique, where several exposures at different shutter speeds are combined to produce an HDR image and a tone mapping operator is then applied to the result. There are now many examples of locally tone mapped digital images, inaccurately known as "HDR photographs", on the internet, and these are of varying quality. This popularity is partly driven by the distinctive appearance of locally tone mapped images, which many people find attractive, and partly by a desire to capture high-contrast scenes that are hard or impossible to photograph in a single exposure, and may not render attractively even when they can be captured. Although digital sensors actually capture a higher dynamic range than film, they completely lose detail in extreme highlights, clipping them to pure white, producing an unattractive result when compared with negative film, which tends to retain color and some detail in highlights.
In some cases local tone mapping is used even though the dynamic range of the source image could be captured on the target media, either to produce the distinctive appearance of a locally tone mapped image, or to produce an image closer to the photographer's artistic vision of the scene by removing sharp contrasts, which often look unattractive. In some cases, tone mapped images are produced from a single exposure which is then manipulated with conventional processing tools to produce the inputs to the HDR image generation process. This avoids the artifacts that can appear when different exposures are combined, due to moving objects in the scene or camera shake. However, when tone mapping is applied to a single exposure in this way, the intermediate image has only normal dynamic range, and the amount of shadow or highlight detail that can be rendered is only that which was captured in the original exposure.
Dodging and burning are terms used in photography for a technique used during the printing process to manipulate the exposure of select areas on a photographic print, deviating from the rest of the image's exposure. In a darkroom print from a film negative, dodging decreases the exposure for areas of the print that the photographer wishes to be lighter, while burning increases the exposure to areas of the print that should be darker.
Any material with varying degrees of opacity may be used, as preferred, to cover and/or obscure the desired area for burning or dodging. One may use a transparency with text, designs, patterns, a stencil, or a completely opaque material shaped according to the desired area of burning/dodging.
Many modern digital image editing programs have "dodge" and "burn" tools that mimic the effect on digital images.
By using completely opaque material as a cover over the preferred area for dodging or burning, absolutely no light will pass through and as a result, an outline of the material may be visible on the print. One way to prevent obvious cover-up lines is to slightly shake the burning material over the covered area while it is being exposed. Another way to prevent obvious cover-up lines is to use slightly less opaque material closer to the outline to produce a more subtle, faded effect.
Techniques
Burning: a darkroom technique
To burn-in a print, the print is first given normal exposure. Next, extra exposure is given to the area or areas that need to be darkened. A card or other opaque object is held between the enlarger lens and the photographic paper in such a way as to allow light to fall only on the portion of the scene to be darkened.
Dodging: also a darkroom technique
A card or other opaque object is held between the enlarger lens and the photographic paper in such a way as to block light from the portion of the scene to be lightened. Since the technique is used with a negative-to-positive process, reducing the amount of light results in a lighter image.
Preflight Check
So-called “preflight checkers” represent a special version of proofing. To avoid the risk of incorrect imaging, above all of PostScript files, preflight checkers carry out a consistency inspection of the files prior to forwarding them to production. Missing type and defective files, which could lead to incorrect imaging or a system crash, are recognized early in this way. The importance of preflight checkers is likely to increase with the growing complexity of the modern data formats. Some software products falling under this category have the function of interpreting PostScript files with a complex structure and converting them into “simple”PostScript data, which, in the majority of cases, can be processed quickly and reliably in any RIP software. Preflight checking has become a special service function for contractors of numerous operations in the graphic arts industry and has also become successful in business models as an additional business for the benefit of all parties (checking the data of the contractor and, if necessary, correcting instead of sending back).