Film_speed

context: Relatively insensitive film, with a correspondingly lower speed index, requires more exposure to light to produce the same image density as a more sensitive film, and is thus commonly termed a slow film. Highly sensitive films are correspondingly termed fast films. In both digital and film photography, the reduction of exposure corresponding to use of higher sensitivities generally leads to reduced image quality (via coarser film grain or higher image noise of other types). In short, the higher the sensitivity, the grainier the image will be. Ultimately sensitivity is limited by the quantum efficiency of the film or sensor.
qas: answers: text: sensitivity
question: What does the film's quantum efficiency limit? 

answers: text: slow film
question: What speed of film is produced by insensitive film? 

answers: text: reduction of exposure
question: What leads to lower quality images?

answers: text: Highly sensitive films
question: What types of film are considered fast films?

answers: text: reduced image quality
question: What effect does highly sensitive film have on images?

context: The Warnerke Standard Sensitometer consisted of a frame holding an opaque screen with an array of typically 25 numbered, gradually pigmented squares brought into contact with the photographic plate during a timed test exposure under a phosphorescent tablet excited before by the light of a burning Magnesium ribbon. The speed of the emulsion was then expressed in 'degrees' Warnerke (sometimes seen as Warn. or °W.) corresponding with the last number visible on the exposed plate after development and fixation. Each number represented an increase of 1/3 in speed, typical plate speeds were between 10° and 25° Warnerke at the time.
qas: answers: text: The Warnerke Standard Sensitometer
question: What consists of 25 pigmented squares touching a plate below a phosphorescent tablet under the light of a burning Magnesium ribbon?

answers: text: The speed of the emulsion
question: What do degrees Warnerke measure?

answers: text: an increase of 1/3 in speed
question: How much speed is associated with each degree Warnerke?

answers: text: between 10° and 25° Warnerke
question: What were usual ranges of Warnerke speeds? 

answers: text: 'degrees' Warnerke
question: What does the last exposed number on the plate represent? 

context: The Scheinergrade (Sch.) system was devised by the German astronomer Julius Scheiner (1858–1913) in 1894 originally as a method of comparing the speeds of plates used for astronomical photography. Scheiner's system rated the speed of a plate by the least exposure to produce a visible darkening upon development. Speed was expressed in degrees Scheiner, originally ranging from 1° Sch. to 20° Sch., where an increment of 19° Sch. corresponded to a hundredfold increase in sensitivity, which meant that an increment of 3° Sch. came close to a doubling of sensitivity.
qas: answers: text: the German astronomer Julius Scheiner
question: Who created the Scheinergrade system? 

answers: text: comparing the speeds of plates used for astronomical photography
question: What is the Scheinergrade system used for?

answers: text: the speed of a plate
question: What do degrees Scheiner indicate?

answers: text: from 1° Sch. to 20° Sch
question: What is the range of Scheiner speeds?

answers: text: an increment of 3° Sch
question: Approximately how many degrees indicate double the sensitivity? 

context: The system was later extended to cover larger ranges and some of its practical shortcomings were addressed by the Austrian scientist Josef Maria Eder (1855–1944) and Flemish-born botanist Walter Hecht (de) (1896–1960), (who, in 1919/1920, jointly developed their Eder–Hecht neutral wedge sensitometer measuring emulsion speeds in Eder–Hecht grades). Still, it remained difficult for manufactures to reliably determine film speeds, often only by comparing with competing products, so that an increasing number of modified semi-Scheiner-based systems started to spread, which no longer followed Scheiner's original procedures and thereby defeated the idea of comparability.
qas: answers: text: Austrian scientist Josef Maria Eder (1855–1944) and Flemish-born botanist Walter Hecht (de)
question: Who developed a device that improved on the shortcomings of Scheiner's invention?

answers: text: emulsion speeds
question: What did the Eder-Hecht device measure?

answers: text: comparing with competing products
question: What method did manufacturers use much of the time to compare film speeds?

answers: text: modified semi-Scheiner-based systems
question: What type of measurement methods began to proliferate?

answers: text: modified semi-Scheiner-based systems
question: What eliminated comparability?

context: The DIN system, officially DIN standard 4512 by Deutsches Institut für Normung (but still named Deutscher Normenausschuß (DNA) at this time), was published in January 1934. It grew out of drafts for a standardized method of sensitometry put forward by Deutscher Normenausschuß für Phototechnik as proposed by the committee for sensitometry of the Deutsche Gesellschaft für photographische Forschung since 1930 and presented by Robert Luther (de) (1868–1945) and Emanuel Goldberg (1881–1970) at the influential VIII. International Congress of Photography (German: Internationaler Kongreß für wissenschaftliche und angewandte Photographie) held in Dresden from August 3 to 8, 1931.
qas: answers: text: January 1934
question: When was the DIN system established? 

answers: text: Deutsches Institut für Normung
question: Who created the DIN system?

answers: text: a standardized method of sensitometry
question: What was proposed at the VIII International Congress of Photography?

answers: text: Robert Luther (de) (1868–1945) and Emanuel Goldberg (1881–1970)
question: Who presented the idea that grew into the DIN?

answers: text: Dresden
question: Where was the VIII International Congress of Photography held?

context: As in the Scheiner system, speeds were expressed in 'degrees'. Originally the sensitivity was written as a fraction with 'tenths' (for example "18/10° DIN"), where the resultant value 1.8 represented the relative base 10 logarithm of the speed. 'Tenths' were later abandoned with DIN 4512:1957-11, and the example above would be written as "18° DIN". The degree symbol was finally dropped with DIN 4512:1961-10. This revision also saw significant changes in the definition of film speeds in order to accommodate then-recent changes in the American ASA PH2.5-1960 standard, so that film speeds of black-and-white negative film effectively would become doubled, that is, a film previously marked as "18° DIN" would now be labeled as "21 DIN" without emulsion changes.
qas: answers: text: degrees
question: What unit was used in the DIN to express speeds? 

answers: text: as a fraction with 'tenths' (for example "18/10° DIN")
question: How was sensitivity expressed at first in the DIN system?

answers: text: with DIN 4512:1961-10
question: When did the degree symbol fall out of use in the DIN system?

answers: text: to accommodate then-recent changes in the American ASA PH2.5-1960 standard
question: Why did the definition of film speeds change considerably?

answers: text: would become doubled
question: What happened to film speeds of black-and-white negative film?

context: On an international level the German DIN 4512 system has been effectively superseded in the 1980s by ISO 6:1974, ISO 2240:1982, and ISO 5800:1979 where the same sensitivity is written in linear and logarithmic form as "ISO 100/21°" (now again with degree symbol). These ISO standards were subsequently adopted by DIN as well. Finally, the latest DIN 4512 revisions were replaced by corresponding ISO standards, DIN 4512-1:1993-05 by DIN ISO 6:1996-02 in September 2000, DIN 4512-4:1985-08 by DIN ISO 2240:1998-06 and DIN 4512-5:1990-11 by DIN ISO 5800:1998-06 both in July 2002.
qas: answers: text: ISO 6:1974, ISO 2240:1982, and ISO 5800:1979
question: What took the place of the German DIN 4512 system?

answers: text: in linear and logarithmic form as "ISO 100/21°"
question: How is sensitivity shown in the ISO systems?

answers: text: ISO standards
question: What standards did the DIN begin to use?

answers: text: in the 1980s
question: When were the ISO standards first adopted?

answers: text: July 2002
question: When were the last ISO standards adopted? 

context: Before the advent of the ASA system, the system of Weston film speed ratings was introduced by Edward Faraday Weston (1878–1971) and his father Dr. Edward Weston (1850–1936), a British-born electrical engineer, industrialist and founder of the US-based Weston Electrical Instrument Corporation, with the Weston model 617, one of the earliest photo-electric exposure meters, in August 1932. The meter and film rating system were invented by William Nelson Goodwin, Jr., who worked for them and later received a Howard N. Potts Medal for his contributions to engineering.
qas: answers: text: the system of Weston film speed ratings
question: What system was used previous to the ASA system?

answers: text: Edward Faraday Weston (1878–1971) and his father Dr. Edward Weston (1850–1936)
question: Who devised the Weston film speed ratings? 

answers: text: the US-based Weston Electrical Instrument Corporation
question: What company did Dr. Edward Weston start? 

answers: text: August 1932
question: When was the Weston model 617 created?

answers: text: William Nelson Goodwin, Jr.
question: Who is credited with creating the film and meter system?

context: The Weston Cadet (model 852 introduced in 1949), Direct Reading (model 853 introduced 1954) and Master III (models 737 and S141.3 introduced in 1956) were the first in their line of exposure meters to switch and utilize the meanwhile established ASA scale instead. Other models used the original Weston scale up until ca. 1955. The company continued to publish Weston film ratings after 1955, but while their recommended values often differed slightly from the ASA film speeds found on film boxes, these newer Weston values were based on the ASA system and had to be converted for use with older Weston meters by subtracting 1/3 exposure stop as per Weston's recommendation. Vice versa, "old" Weston film speed ratings could be converted into "new" Westons and the ASA scale by adding the same amount, that is, a film rating of 100 Weston (up to 1955) corresponded with 125 ASA (as per ASA PH2.5-1954 and before). This conversion was not necessary on Weston meters manufactured and Weston film ratings published since 1956 due to their inherent use of the ASA system; however the changes of the ASA PH2.5-1960 revision may be taken into account when comparing with newer ASA or ISO values.
qas: answers: text: The Weston Cadet (model 852 introduced in 1949), Direct Reading (model 853 introduced 1954) and Master III (models 737 and S141.3 introduced in 1956)
question: Which cameras were first of their type to adopt the ASA scale?

answers: text: the ASA system
question: What were updated Weston values based on?

answers: text: by subtracting 1/3 exposure stop
question: How were Weston values changed to ASA values?

answers: text: 1956
question: Beginning with which year was the Weston to ASA conversion not necessary?

answers: text: 1955
question: Until what year did other models use the original Weston scale?

context: General Electric switched to use the ASA scale in 1946. Meters manufactured since February 1946 were equipped with the ASA scale (labeled "Exposure Index") already. For some of the older meters with scales in "Film Speed" or "Film Value" (e.g. models DW-48, DW-49 as well as early DW-58 and GW-68 variants), replaceable hoods with ASA scales were available from the manufacturer. The company continued to publish recommended film values after that date, however, they were now aligned to the ASA scale.
qas: answers: text: General Electric
question: Which company adopted the ASA scale in 1946?

answers: text: 1946
question: Beginning what year were cameras built with the ASA meter?

answers: text: replaceable hoods with ASA scales
question: How did older models convert to ASA scale?

answers: text: labeled "Exposure Index"
question: How was the ASA scale shown on models built after 1946?

answers: text: they were now aligned to the ASA scale
question: What were recommended film values lined up with after 1946?

context: Based on earlier research work by Loyd Ancile Jones (1884–1954) of Kodak and inspired by the systems of Weston film speed ratings and General Electric film values, the American Standards Association (now named ANSI) defined a new method to determine and specify film speeds of black-and-white negative films in 1943. ASA Z38.2.1-1943 was revised in 1946 and 1947 before the standard grew into ASA PH2.5-1954. Originally, ASA values were frequently referred to as American standard speed numbers or ASA exposure-index numbers. (See also: Exposure Index (EI).)
qas: answers: text: Loyd Ancile Jones
question: Who pioneered research that led to the new ANSI values?

answers: text: Weston film speed ratings and General Electric film values
question: What standards were the ANSI developed from?

answers: text: black-and-white negative films
question: What types of film did the ANSI measure?

answers: text: 1943
question: When did the ANSI define its new measure?

answers: text: American standard speed numbers or ASA exposure-index numbers
question: What were ANSI values often called in the beginning?

context: The ASA standard underwent a major revision in 1960 with ASA PH2.5-1960, when the method to determine film speed was refined and previously applied safety factors against under-exposure were abandoned, effectively doubling the nominal speed of many black-and-white negative films. For example, an Ilford HP3 that had been rated at 200 ASA before 1960 was labeled 400 ASA afterwards without any change to the emulsion. Similar changes were applied to the DIN system with DIN 4512:1961-10 and the BS system with BS 1380:1963 in the following years.
qas: answers: text: 1960
question: In what year were big changes made to the ANSI?

answers: text: effectively doubling the nominal speed of many black-and-white negative films
question: What did the 1960 changes to film speed measures lead to?

answers: text: the DIN system
question: Which other system were these changes applied to?

answers: text: 1963
question: In what year was the BS system modified?

answers: text: safety factors against under-exposure
question: What safety factors were done away with beginning with the modifications to the standards?

context: Film speed is found from a plot of optical density vs. log of exposure for the film, known as the D–log H curve or Hurter–Driffield curve. There typically are five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region. For black-and-white negative film, the “speed point” m is the point on the curve where density exceeds the base + fog density by 0.1 when the negative is developed so that a point n where the log of exposure is 1.3 units greater than the exposure at point m has a density 0.8 greater than the density at point m. The exposure Hm, in lux-s, is that for point m when the specified contrast condition is satisfied. The ISO arithmetic speed is determined from:
qas: answers: text: the D–log H curve or Hurter–Driffield curve
question: What is the plot from which film speed is derived called?

answers: text: five
question: How many regions does the Hurter-Driffield curve have?

answers: text: a plot of optical density vs. log of exposure for the film
question: What is plotted in the Hurter-Driffield curve?

answers: text: The exposure Hm, in lux-s
question: What is denoted when the specified contrast condition is met?

answers: text: the base + fog, the toe, the linear region, the shoulder, and the overexposed region
question: What are the five regions of the Hurter-Driffield curve?

context: Film speed is used in the exposure equations to find the appropriate exposure parameters. Four variables are available to the photographer to obtain the desired effect: lighting, film speed, f-number (aperture size), and shutter speed (exposure time). The equation may be expressed as ratios, or, by taking the logarithm (base 2) of both sides, by addition, using the APEX system, in which every increment of 1 is a doubling of exposure; this increment is commonly known as a "stop". The effective f-number is proportional to the ratio between the lens focal length and aperture diameter, the diameter itself being proportional to the square root of the aperture area. Thus, a lens set to f/1.4 allows twice as much light to strike the focal plane as a lens set to f/2. Therefore, each f-number factor of the square root of two (approximately 1.4) is also a stop, so lenses are typically marked in that progression: f/1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc.
qas: answers: text: the ratio between the lens focal length and aperture diameter
question: What is the effective f-number proportional to?

answers: text: Film speed
question: What is used to discover the right exposure parameters?

answers: text: lighting, film speed, f-number (aperture size), and shutter speed (exposure time)
question: What variables help the photographer produce the desired effect?

answers: text: twice as much
question: A lens with a setting of f/1.4 lets how much to hit the focal plane compared with a setting of f/2?

answers: text: "stop"
question: In the APEX system, the increment that doubles the exposure is called what?

context: Upon exposure, the amount of light energy that reaches the film determines the effect upon the emulsion. If the brightness of the light is multiplied by a factor and the exposure of the film decreased by the same factor by varying the camera's shutter speed and aperture, so that the energy received is the same, the film will be developed to the same density. This rule is called reciprocity. The systems for determining the sensitivity for an emulsion are possible because reciprocity holds. In practice, reciprocity works reasonably well for normal photographic films for the range of exposures between 1/1000 second to 1/2 second. However, this relationship breaks down outside these limits, a phenomenon known as reciprocity failure.
qas: answers: text: the amount of light energy that reaches the film
question: What determines the effect on the emulsion after exposure?

answers: text: between 1/1000 second to 1/2 second
question: In what range of exposures does reciprocity usually work?

answers: text: by varying the camera's shutter speed and aperture
question: How is the exposure of film changed?

answers: text: because reciprocity holds
question: How are ways of finding an emulsion's sensitivity possible?

answers: text: reciprocity failure
question: What happens outside the 1/1000 second to 1/second exposure range?

context: Some high-speed black-and-white films, such as Ilford Delta 3200 and Kodak T-MAX P3200, are marketed with film speeds in excess of their true ISO speed as determined using the ISO testing method. For example, the Ilford product is actually an ISO 1000 film, according to its data sheet. The manufacturers do not indicate that the 3200 number is an ISO rating on their packaging. Kodak and Fuji also marketed E6 films designed for pushing (hence the "P" prefix), such as Ektachrome P800/1600 and Fujichrome P1600, both with a base speed of ISO 400.
qas: answers: text: Ilford Delta 3200 and Kodak T-MAX P3200
question: What are two examples of films that are marketed with speeds above their true ISO speed?

answers: text: ISO 1000
question: What speed of film is the Ilford Delta 3200?

answers: text: Kodak and Fuji
question: Which two companies produced E6 films meant for "pushing"?

answers: text: ISO 400
question: What is the base speed of Ektachrome P800/1600 and Fujichrome P1600?

answers: text: high-speed black-and-white films
question: What type of films are Ilford Delta 3200 and Kodak T-MAX P3200?

context: For digital photo cameras ("digital still cameras"), an exposure index (EI) rating—commonly called ISO setting—is specified by the manufacturer such that the sRGB image files produced by the camera will have a lightness similar to what would be obtained with film of the same EI rating at the same exposure. The usual design is that the camera's parameters for interpreting the sensor data values into sRGB values are fixed, and a number of different EI choices are accommodated by varying the sensor's signal gain in the analog realm, prior to conversion to digital. Some camera designs provide at least some EI choices by adjusting the sensor's signal gain in the digital realm. A few camera designs also provide EI adjustment through a choice of lightness parameters for the interpretation of sensor data values into sRGB; this variation allows different tradeoffs between the range of highlights that can be captured and the amount of noise introduced into the shadow areas of the photo.
qas: answers: text: ISO setting
question: What is another name for an exposure index rating?

answers: text: by adjusting the sensor's signal gain in the digital realm
question: How do some camera designs give some EI choices?

answers: text: the manufacturer
question: Who provides the exposure index rating?

answers: text: digital still cameras
question: What are digital photo cameras also called?

context: Digital cameras have far surpassed film in terms of sensitivity to light, with ISO equivalent speeds of up to 409,600, a number that is unfathomable in the realm of conventional film photography. Faster processors, as well as advances in software noise reduction techniques allow this type of processing to be executed the moment the photo is captured, allowing photographers to store images that have a higher level of refinement and would have been prohibitively time consuming to process with earlier generations of digital camera hardware.
qas: answers: text: Digital cameras
question: What types of cameras have proven to be much more sensitive to light than film?

answers: text: 409,600
question: What ISO equivalent speeds can digital cameras obtain?

answers: text: Faster processors, as well as advances in software noise reduction techniques
question: What is responsible for these vast increases in speed?

answers: text: prohibitively time consuming to process
question: What is one thing that limited speeds of older digital hardware?

answers: text: a higher level of refinement
question: What does the higher speed do for the images produced?

context: The ISO standard ISO 12232:2006 gives digital still camera manufacturers a choice of five different techniques for determining the exposure index rating at each sensitivity setting provided by a particular camera model. Three of the techniques in ISO 12232:2006 are carried over from the 1998 version of the standard, while two new techniques allowing for measurement of JPEG output files are introduced from CIPA DC-004. Depending on the technique selected, the exposure index rating can depend on the sensor sensitivity, the sensor noise, and the appearance of the resulting image. The standard specifies the measurement of light sensitivity of the entire digital camera system and not of individual components such as digital sensors, although Kodak has reported using a variation to characterize the sensitivity of two of their sensors in 2001.
qas: answers: text: five
question: How many techniques are available because of ISO 12232:2006?

answers: text: two new techniques allowing for measurement of JPEG output files
question: What techniques did CIPA DC-004 provide?

answers: text: the sensor sensitivity, the sensor noise, and the appearance of the resulting image
question: What factors affect the exposure index rating?

answers: text: the measurement of light sensitivity of the entire digital camera system and not of individual components
question: What does the standard of ISO 12232:2006 specify?

answers: text: 2001
question: In what year did Kodak start using a different way of characterizing two sensors?

context: The Recommended Exposure Index (REI) technique, new in the 2006 version of the standard, allows the manufacturer to specify a camera model’s EI choices arbitrarily. The choices are based solely on the manufacturer’s opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings. This is the only technique available under the standard for output formats that are not in the sRGB color space. This is also the only technique available under the standard when multi-zone metering (also called pattern metering) is used.
qas: answers: text: to specify a camera model’s EI choices arbitrarily
question: What option does the Recommended Exposure Index give manufacturers? 

answers: text: pattern metering
question: What is another name for multi-zone metering?

answers: text: the only technique available under the standard for output formats that are not in the sRGB color space
question: What distinction does the Recommended Exposure Index have?

answers: text: 2006
question: When was the Recommended Exposure Index introduced?

answers: text: Recommended Exposure Index (REI) technique
question: What is the only technique that can be used when multi-zone metering is used?

context: The Standard Output Sensitivity (SOS) technique, also new in the 2006 version of the standard, effectively specifies that the average level in the sRGB image must be 18% gray plus or minus 1/3 stop when the exposure is controlled by an automatic exposure control system calibrated per ISO 2721 and set to the EI with no exposure compensation. Because the output level is measured in the sRGB output from the camera, it is only applicable to sRGB images—typically JPEG—and not to output files in raw image format. It is not applicable when multi-zone metering is used.
qas: answers: text: 2006
question: What year was the Standard Output Sensitivity technique introduced?

answers: text: sRGB images—typically JPEG
question: What does the Standard Output Sensitivity technique apply to?

answers: text: the sRGB output from the camera
question: What is the output level measured in?

answers: text: multi-zone metering
question: With what type of metering can the Standard Output Sensitivity not be used?

answers: text: ISO 2721
question: With what standard is the automatic exposure control system calibrated?

context: The CIPA DC-004 standard requires that Japanese manufacturers of digital still cameras use either the REI or SOS techniques, and DC-008 updates the Exif specification to differentiate between these values. Consequently, the three EI techniques carried over from ISO 12232:1998 are not widely used in recent camera models (approximately 2007 and later). As those earlier techniques did not allow for measurement from images produced with lossy compression, they cannot be used at all on cameras that produce images only in JPEG format.
qas: answers: text: REI or SOS techniques
question: Which methods are required by CIPA DC-004?

answers: text: approximately 2007 and later
question: In what year did the three EI techniques from ISO 12232:1998 largely stop being used?

answers: text: cameras that produce images only in JPEG format
question: With what cameras can earlier techniques not be used?

answers: text: Japanese
question: What nation's cameras does the CIPA DC-004 apply to?

answers: text: the Exif specification
question: What does the DC-008 change?

context: where  is the maximum possible exposure that does not lead to a clipped or bloomed camera output. Typically, the lower limit of the saturation speed is determined by the sensor itself, but with the gain of the amplifier between the sensor and the analog-to-digital converter, the saturation speed can be increased. The factor 78 is chosen such that exposure settings based on a standard light meter and an 18-percent reflective surface will result in an image with a grey level of 18%/√2 = 12.7% of saturation. The factor √2 indicates that there is half a stop of headroom to deal with specular reflections that would appear brighter than a 100% reflecting white surface.
qas: answers: text: lower limit of the saturation speed
question: What does the sensor usually determine?

answers: text: with the gain of the amplifier between the sensor and the analog-to-digital converter
question: How can the saturation speed be increased?

answers: text: there is half a stop of headroom to deal with specular reflections that would appear brighter than a 100% reflecting white surface
question: What is indicated by the factor √2?

answers: text: clipped or bloomed camera output
question: What can too much exposure lead to?

context: The noise-based speed is defined as the exposure that will lead to a given signal-to-noise ratio on individual pixels. Two ratios are used, the 40:1 ("excellent image quality") and the 10:1 ("acceptable image quality") ratio. These ratios have been subjectively determined based on a resolution of 70 pixels per cm (178 DPI) when viewed at 25 cm (9.8 inch) distance. The signal-to-noise ratio is defined as the standard deviation of a weighted average of the luminance and color of individual pixels. The noise-based speed is mostly determined by the properties of the sensor and somewhat affected by the noise in the electronic gain and AD converter.
qas: answers: text: the 40:1 ("excellent image quality") and the 10:1 ("acceptable image quality") ratio
question: Which ratios are employed to calculate noise-based speed?

answers: text: the exposure that will lead to a given signal-to-noise ratio on individual pixels
question: What is the noise-based speed?

answers: text: subjectively determined based on a resolution of 70 pixels per cm (178 DPI) when viewed at 25 cm (9.8 inch) distance
question: How are the two ratios found?

answers: text: the standard deviation of a weighted average of the luminance and color of individual pixels
question: What is a definition of signal-to-noise ratio?

answers: text: the properties of the sensor and somewhat affected by the noise in the electronic gain and AD converter
question: What factors influence the noise-based speed?

context: The standard specifies how speed ratings should be reported by the camera. If the noise-based speed (40:1) is higher than the saturation-based speed, the noise-based speed should be reported, rounded downwards to a standard value (e.g. 200, 250, 320, or 400). The rationale is that exposure according to the lower saturation-based speed would not result in a visibly better image. In addition, an exposure latitude can be specified, ranging from the saturation-based speed to the 10:1 noise-based speed. If the noise-based speed (40:1) is lower than the saturation-based speed, or undefined because of high noise, the saturation-based speed is specified, rounded upwards to a standard value, because using the noise-based speed would lead to overexposed images. The camera may also report the SOS-based speed (explicitly as being an SOS speed), rounded to the nearest standard speed rating.
qas: answers: text: from the saturation-based speed to the 10:1 noise-based speed
question: What is the range for exposure latitude?

answers: text: SOS-based speed
question: What is another speed that can also be reported by the camera?

answers: text: the noise-based speed (40:1) is higher than the saturation-based speed
question: When should the noise-based speed be used?

answers: text: exposure according to the lower saturation-based speed would not result in a visibly better image
question: Why should noise-based speed be rounded down to a lower standard?

answers: text: how speed ratings should be reported by the camera
question: What does the standard specify?

context: Despite these detailed standard definitions, cameras typically do not clearly indicate whether the user "ISO" setting refers to the noise-based speed, saturation-based speed, or the specified output sensitivity, or even some made-up number for marketing purposes. Because the 1998 version of ISO 12232 did not permit measurement of camera output that had lossy compression, it was not possible to correctly apply any of those measurements to cameras that did not produce sRGB files in an uncompressed format such as TIFF. Following the publication of CIPA DC-004 in 2006, Japanese manufacturers of digital still cameras are required to specify whether a sensitivity rating is REI or SOS.[citation needed]
qas: answers: text: the noise-based speed, saturation-based speed, or the specified output sensitivity, or even some made-up number for marketing purposes
question: What measures might the user "ISO" setting correspond to?

answers: text: measurement of camera output that had lossy compression
question: What did the 1998 version of ISO 12232 not permit?

answers: text: REI or SOS
question: What types of sensitivity ratings can be specified by a camera?

answers: text: CIPA DC-004
question: What standards changed what Japanese camera makers have to specify?

answers: text: 2006
question: In what year was CIPA DC-004 introduced?