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35-400: The E-PM1 was announced on June 30, 2011 together with two other Olympus Micro Four Thirds cameras, EP3 and E-PL3. Reviewers generally praised the image quality and wide range of customization it offers, although there were some criticisms of its performance. The small size also divided reviewers, with some praising its compactness and others criticising it as difficult to handle and noting that

70-408: A 3x3 matrix . This type of transformation is appropriate if the image was captured using the wrong white balance setting on a digital camera, or through a color filter. In principle, one wants to scale all relative luminances in an image so that objects which are believed to be neutral appear so. If, say, a surface with R = 240 {\displaystyle R=240} was believed to be

105-426: A button on a camera is a way for the user to indicate to the processor the nature of the scene lighting. Another option on some cameras is a button which one may press when the camera is pointed at a gray card or other neutral colored object. This captures an image of the ambient light, which enables a digital camera to set the correct color balance for that light. There is a large literature on how one might estimate

140-431: A change in illuminant is not necessarily a diagonal matrix in a fixed color space. It has long been known that if the space of illuminants can be described as a linear model with N basis terms, the proper color transformation will be the weighted sum of N fixed linear transformations, not necessarily consistently diagonalizable. Gray card A gray card is a middle gray reference, typically used together with

175-535: A compromise between the small size and lack of physical controls, making it harder to quickly change between modes and settings, but found it was a good upgrade from a compact digital camera . No Video | Weather Sealed | All the Rest Auto white balance In photography and image processing , color balance is the global adjustment of the intensities of the colors (typically red, green, and blue primary colors ). An important goal of this adjustment

210-465: A displayed image appear to have the same general appearance as the colors in an original scene. It is particularly important that neutral (gray, neutral, white) colors in a scene appear neutral in the reproduction. Humans relate to flesh tones more critically than other colors. Trees, grass and sky can all be off without concern, but if human flesh tones are 'off' then the human subject can look sick or dead. To address this critical color balance issue,

245-422: A factor of more than two in favor of camera RGB. This means that it is advantageous to get color balance right at the time an image is captured, rather than edit later on a monitor. If one must color balance later, balancing the raw image data will tend to produce less distortion of chromatic colors than balancing in monitor RGB. Color balancing is sometimes performed on a three-component image (e.g., RGB ) using

280-425: A matrix P {\displaystyle \mathbf {P} } so that: where L R {\displaystyle L_{R}} , L G {\displaystyle L_{G}} , and L B {\displaystyle L_{B}} are the un- gamma corrected monitor RGB, one may use: Johannes von Kries , whose theory of rods and three color-sensitive cone types in

315-421: A number of different RGB spaces have identified several such spaces that work better than others, and better than camera or monitor spaces, for chromatic adaptation, as measured by several color appearance models ; the systems that performed statistically as well as the best on the majority of the image test sets used were the "Sharp", "Bradford", "CMCCAT", and "ROMM" spaces. The best color matrix for adapting to

350-535: A reflective light meter , as a way to produce consistent image exposure and/or color in video production , film , and photography . A gray card is a flat object of a neutral-gray color that derives from a flat reflectance spectrum. A typical example is the Kodak R-27 set, which contains one 8 in × 10 in (20 cm × 25 cm) card and one 4 in × 5 in (10 cm × 13 cm) card, each with an 18% reflectance across

385-443: A white object, and if 255 is the count which corresponds to white, one could multiply all red values by 255/240. Doing analogously for green and blue would result, at least in theory, in a color balanced image. In this type of transformation the 3x3 matrix is a diagonal matrix . where R {\displaystyle R} , G {\displaystyle G} , and B {\displaystyle B} are

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420-403: Is one of the most common kinds of balancing, and is when colors are adjusted to make a white object (such as a piece of paper or a wall) appear white and not a shade of any other colour. Image data acquired by sensors – either film or electronic image sensors – must be transformed from the acquired values to new values that are appropriate for color reproduction or display. Several aspects of

455-413: Is to provide a standard reference object for exposure determination in photography. A gray card is an (approximate) realization of a Lambertian scatterer; its apparent brightness (and exposure determination) therefore depends only on its orientation relative to the light source. To establish the exposure for a photograph Kodak recommends placing the gray card as close to the subject as possible and "aiming

490-436: Is to render specific colors – particularly neutral colors like white or grey – correctly. Hence, the general method is sometimes called gray balance , neutral balance , or white balance . Color balance changes the overall mixture of colors in an image and is used for color correction . Generalized versions of color balance are used to correct colors other than neutrals or to deliberately change them for effect. White balance

525-477: The illuminant under which an image was captured; and second, scaling the components (e.g., R, G, and B) of the image or otherwise transforming the components so they conform to the viewing illuminant. Viggiano found that white balancing in the camera's native RGB color model tended to produce less color inconstancy (i.e., less distortion of the colors) than in monitor RGB for over 4000 hypothetical sets of camera sensitivities. This difference typically amounted to

560-508: The retina has survived as the dominant explanation of color sensation for over 100 years, motivated the method of converting color to the LMS color space , representing the effective stimuli for the Long-, Medium-, and Short-wavelength cone types that are modeled as adapting independently. A 3x3 matrix converts RGB or XYZ to LMS, and then the three LMS primary values are scaled to balance the neutral;

595-418: The visible spectrum , and a white reverse side with a 90% reflectance. Note that flat spectral reflectance is a stronger condition than simply appearing neutral; this flatness ensures that the card always has the same color as its illuminant (see metamerism ). Gray cards are used in a variety of ways by photographers, cinematographers, video engineers and video camera operators. A primary use of gray cards

630-423: The acquisition and display process make such color correction essential – including that the acquisition sensors do not match the sensors in the human eye, that the properties of the display medium must be accounted for, and that the ambient viewing conditions of the acquisition differ from the display viewing conditions. The color balance operations in popular image editing applications usually operate directly on

665-406: The ambient lighting from the camera data and then use this information to transform the image data. A variety of algorithms have been proposed, and the quality of these has been debated. A few examples and examination of the references therein will lead the reader to many others. Examples are Retinex , an artificial neural network or a Bayesian method . Color balancing an image affects not only

700-420: The camera to compensate for the illuminant color in a scene. Gray cards can be used for in-camera white balance or post-processing white balance. Many digital cameras have a custom white balance feature. A photo of the gray card is taken and used to set white balance for a sequence of photos. For post-processing white balance, a photo of the gray card in the scene is taken, and the image processing software uses

735-591: The color balanced red, green, and blue components of a pixel in the image; R ′ {\displaystyle R'} , G ′ {\displaystyle G'} , and B ′ {\displaystyle B'} are the red, green, and blue components of the image before color balancing, and R w ′ {\displaystyle R'_{w}} , G w ′ {\displaystyle G'_{w}} , and B w ′ {\displaystyle B'_{w}} are

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770-515: The color can then be converted back to the desired final color space : where L {\displaystyle L} , M {\displaystyle M} , and S {\displaystyle S} are the color-balanced LMS cone tristimulus values; L w ′ {\displaystyle L'_{w}} , M w ′ {\displaystyle M'_{w}} , and S w ′ {\displaystyle S'_{w}} are

805-597: The color-balanced tristimulus values; X w {\displaystyle X_{w}} , Y w {\displaystyle Y_{w}} , and Z w {\displaystyle Z_{w}} are the tristimulus values of the viewing illuminant (the white point to which the image is being transformed to conform to); X w ′ {\displaystyle X'_{w}} , Y w ′ {\displaystyle Y'_{w}} , and Z w ′ {\displaystyle Z'_{w}} are

840-491: The data from the pixels in the gray card area of the photo to set the white balance point for the whole image. Gray cards are made of a variety of materials including fabric, plastic, paper, and foam. A gray card is useful for setting or correcting the balance of neutral colors, as well as for exposure. Other charts, such as various color charts , provide standard reference patterns with calibrated reflectance spectrum and color coordinates, for use in adjusting color rendering in

875-466: The exposure parameters using these criteria: This technique is similar to using an incident meter, as it depends on the illuminance but not the reflectivity of the subject. (Of course taking photographs with side lighting or back lighting implies that the gray card should be oriented toward the camera instead.) In addition to providing a means for measuring exposure, a gray card provides a convenient reference for white balance, or color balance , allowing

910-520: The lack of external controls making it hard to quickly change settings. DP Review rated it 71% and a silver award, praising its image quality, small size, and wide range of customisable features. What Digital Camera called it "an easy to use camera" while criticising the auto white balance accuracy, weak performance in low light, and lack of physical grip on the camera body. Expert Reviews gave it 4/5, praising its flexibility and good value while calling it "far from perfect". PC Advisor noted

945-462: The latter are specified; matrices can also be found in reference books. By Viggiano's measure, and using his model of gaussian camera spectral sensitivities, most camera RGB spaces performed better than either monitor RGB or XYZ. If the camera's raw RGB values are known, one may use the 3x3 diagonal matrix: and then convert to a working RGB space such as sRGB or Adobe RGB after balancing. Comparisons of images balanced by diagonal transforms in

980-546: The neutral surfaces perfectly neutral. If the image may be transformed into CIE XYZ tristimulus values , the color balancing may be performed there. This has been termed a "wrong von Kries" transformation. Although it has been demonstrated to offer usually poorer results than balancing in monitor RGB, it is mentioned here as a bridge to other things. Mathematically, one computes: where X {\displaystyle X} , Y {\displaystyle Y} , and Z {\displaystyle Z} are

1015-550: The neutrals, but other colors as well. An image that is not color balanced is said to have a color cast , as everything in the image appears to have been shifted towards one color. Color balancing may be thought in terms of removing this color cast. Color balance is also related to color constancy . Algorithms and techniques used to attain color constancy are frequently used for color balancing, as well. Color constancy is, in turn, related to chromatic adaptation . Conceptually, color balancing consists of two steps: first, determining

1050-418: The red, green, and blue channel pixel values, without respect to any color sensing or reproduction model. In film photography, color balance is typically achieved by using color correction filters over the lights or on the camera lens. Sometimes the adjustment to keep neutrals neutral is called white balance , and the phrase color balance refers to the adjustment that in addition makes other colors in

1085-495: The red, green, and blue components of a pixel which is believed to be a white surface in the image before color balancing. This is a simple scaling of the red, green, and blue channels, and is why color balance tools in Photoshop have a white eyedropper tool. It has been demonstrated that performing the white balancing in the phosphor set assumed by sRGB tends to produce large errors in chromatic colors, even though it can render

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1120-432: The surface of the gray card toward a point one third of the compound angle between the camera and the main light. For example, if the main light is located 30 degrees to the side and 45 degrees up from the camera-to subject axis, aim the card 10 degrees to the side and 15 degrees up." The card should be metered from approximately six inches (15 cm) away. Once a meter reading has been obtained, Kodak further recommends adjusting

1155-539: The tri-color primaries themselves are formulated to not balance as a true neutral color. The purpose of this color primary imbalance is to more faithfully reproduce the flesh tones through the entire brightness range. Most digital cameras have means to select color correction based on the type of scene lighting, using either manual lighting selection, automatic white balance, or custom white balance. The algorithms for these processes perform generalized chromatic adaptation . Many methods exist for color balancing. Setting

1190-516: The tristimulus values of an object believed to be white in the un-color-balanced image, and L ′ {\displaystyle L'} , M ′ {\displaystyle M'} , and S ′ {\displaystyle S'} are the tristimulus values of a pixel in the un-color-balanced image. Matrices to convert to LMS space were not specified by von Kries, but can be derived from CIE color matching functions and LMS color matching functions when

1225-415: The tristimulus values of an object believed to be white in the un-color-balanced image, and X ′ {\displaystyle X'} , Y ′ {\displaystyle Y'} , and Z ′ {\displaystyle Z'} are the tristimulus values of a pixel in the un-color-balanced image. If the tristimulus values of the monitor primaries are in

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