Film speed is a measure of the sensitivity of photographic film to light, determined by sensitometry and measured on various numerical scales, the most recent being an ISO system. The closely-tied ISO system is used to illustrate the relationship between exposure and the brightness of the image output in a digital camera.
Relatively insensitive films, with lower speed indexes, require more light exposure to produce the same image density as the more sensitive films, and thus are usually referred to as slow film . Highly sensitive movies simultaneously called fast movies . In digital and film photography, reduced exposure associated with higher sensitivity use generally leads to image degradation (through coarse film grain or higher image noise than other types). In short, the higher the sensitivity, the more images are generated. The sensitivity is ultimately limited by the quantum efficiency of the film or sensor.
Video Film speed
Film speed measurement system
Historical system
Warnerke
The first known practical sensitometer, which allowed the measurement of the speed of photographic material, was invented by Polish engineer Leon Warnerke - a Polish name W? Adys? Aw Ma? Achowski (1837-1900) - in 1880, among the achievements to which he was awarded the British Photographic Society Progress Medal in 1882. It was commercialized since 1881.
The Warnerke Standard Sensitometer consists of a framed opaque screen frame with an array of typically 25 numbers, gradually pigmented boxes are brought into contact with the photographic plate during exposure to the timed test under glowing tablets that are vibrant before by the light of the Magnesium tape on fire. The emulsion velocity is then expressed in Warner's degree (sometimes seen as Warn or ° ° W) according to the last number seen on the exposed plates after development and fixation. Each number represents an increase of 1/3 in speed, typical plate speed between 10 ° and 25 ° Warnerke at the time.
The system saw some success but proved unreliable because of the sensitivity of the spectrum to light, the intensity of fading from the light emitted by the phosphorescent tablets after excitation as well as high tolerance. The concept, however, was then built upon in 1900 by Henry Chapman Jones (1855-1932) in the development of plate tester and modified speed system.
Hurter & amp; Driffield
Another early practical system for measuring emulsion sensitivity was from Hurter and Driffield (H & D), originally described in 1890, by Swiss-born Ferdinand Hurter (1844-1898) and English Vero Charles Driffield (1848-1915). In their system, the speed rate is inversely proportional to the required exposure. For example, an emulsion rated 250 H & amp; D will require ten times the exposure of an emulsion rated 2500 H & amp; D.
The method for determining sensitivity was then modified in 1925 (in relation to the light source used) and in 1928 (regarding light sources, developers and proportional factors) - this variant was later sometimes called "H & D 10". H & amp; D was officially accepted as a standard in the former Soviet Union from 1928 to September 1951, when it was replaced by GOST 2817-50.
Scheiner
The Scheinergrade System (Sch.) Designed by the German astronomer Julius Scheiner (1858-1913) in 1894 originally as a method to compare the speed of plates used for astronomical photography. The Scheiner system assesses the velocity of the plates by the least exposure to produce visible embezzlement on development. Speed ​​is expressed in Scheiner degrees, initially ranging from 1 ° Sch. to 20 Â ° Sch., where an increase of 19 Â ° Sch. associated with a hundredfold increase in sensitivity, which means an increase of 3 ° Sch. nearly doubling the sensitivity.
The system was later expanded to cover a larger range and some of its practical shortcomings were addressed by Austrian scientist Josef Maria Eder (1855-1944) and Flemish-born botanist Walter Hecht (1896-1960), who, in 1919/1920, developed their Eder-Hecht neutral wedge sensitometer measuring emulsion velocity in the Eder-Hecht class). However, it remains difficult for manufacturers to reliably determine the speed of film, often only by comparing with competing products, so that more modified modified semi-Scheiner systems begin to spread, which no longer follow Scheiner's original procedures and thus defeat comparative ideas.
The Scheiner system was eventually abandoned in Germany, when the standard DIN system was introduced in 1934. In various forms, the system continued to be widely used in other countries for some time.
DIN
The DIN system, officially the DIN standard 4512 by the German Deutsches Institut fÃÆ'¼r Normung (but still named Deutscher NormenausschuÃÆ'Ÿ (DNA) at this time), published in January 1934. Growing from the concept to the standard method of sensitometry put forward by < span lang = "de" title = "German text"> Deutscher NormenausschuÃÆ'Ÿ fÃÆ'¼r Phototechnik as proposed by the committee for the sensitometry of Deutsche Gesellschaft förr Forschung photographische since 1930 and presented by Robert Luther (1868-1945) and Emanuel Goldberg (1881-1970) on influential VIII. International Congress of Photography (Germany: Internationaler KongreÃÆ'Ÿ fÃÆ'¼r wissenschaftliche and angewandte Photographie) were held in Dresden from 3 to 8 August, 1931.
Sistem DIN terinspirasi oleh sistem Scheiner, tetapi kepekaan direpresentasikan sebagai logaritma basis 10 dari sensitivitas dikalikan dengan 10, mirip dengan desibel. Jadi peningkatan 20 Â ° (dan bukan 19 Â ° seperti dalam sistem Scheiner) menunjukkan peningkatan sensitivitas seratus kali lipat, dan perbedaan 3 Â ° lebih dekat dengan logaritma basis 10 dari 2 (0,30103...):
As in the Scheiner system, speed is expressed in 'degrees'. Initially sensitivity is written as fractions with 'tenth' (eg "18/10Ã, Â ° DIN"), where the resultant value of 1.8 represents the base 10 logarithm relative to the velocity. 'Tenth' is then left with DIN 4512: 1957-11, and the above example will be written as "18 Â ° DIN". The degree symbol was finally dropped with DIN 4512: 1961-10. This revision also sees a significant change in the definition of film speed to accommodate recent changes in the ASA standard PH2.5-1960, so that the speed of black and white negative film films will be doubled, ie, films previously marked as "18 Â ° DIN "will now be labeled as" 21 DIN "without emulsion change.
Originally intended only for black and white negative films, the system was then extended and reassembled into nine sections, including DIN 4512-1: 1971-04 for the black-and-white negative film DIN 4512-4: 1977-06 for color reversal films and DIN 4512-5: 1977-10 for color negative film.
At the international level, the German DIN 4512 system was effectively replaced in the 1980s by ISO 6: 1974, ISO 2240: 1982, and ISO 5800: 1979 where the same sensitivity was written in linear and logarithmic form as "ISO 100/21Ã , Â ° "(Now again with a degree symbol). This ISO standard is then adopted by DIN as well. Finally, the latest revision of DIN 4512 was replaced with the appropriate 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 in July 2002.
BSI
The film speed scale recommended by the British Standards Institution (BSI) is almost identical to the DIN system except that the BS number is 10 degrees larger than the DIN number.
Weston
Prior to the advent of the ASA system, the Weston speed movie system was introduced by Edward Faraday Weston (1878-1971) and his father. Edward Weston (1850-1936), an American-born electrical engineer, industrialist, and founder of Weston Electrical Instrument Corporation based in the United States, modeled Weston 617, one of the earliest electric photo exposure meters, in August 1932. the film was created by William Nelson Goodwin, Jr., who worked for them and later received the Howard N. Potts Medal for his contributions to engineering.
The company tested and published a speed rating for most movies at the time. The Weston film speed rating has since been found on most of Weston's exposure meters and is sometimes referred to by film manufacturers and third parties in their exposure guidelines. Because manufacturing is sometimes creative about the speed of film, companies go so far as to warn users about unauthorized use of their movie ratings in their "Weston movie ratings" booklet.
The Weston Cadet (model 852 introduced in 1949), Direct Reading (853 model introduced 1954) and Master III (model 737 and S141.3 introduced in 1956) were the first in their exposure meter line to switch and utilize ASA while established scale instead. Other models use the original Weston scale up to ca. 1955. The company continued to publish ratings of Weston movies after 1955, but while their recommended values ​​often differ slightly from the speed of ASA films found on movie boxes, these newer Weston values ​​are based on the ASA system and must be converted for use with those older. Weston meters by reducing the 1/3 exposure stops as per Weston's recommendation. In contrast, the speed ratings of the "old" Weston film can be converted to "new" Weston and ASA scale by adding the same amount, that is, the 100 Weston film rating (up to 1955) corresponds to 125 ASA (ASA). PH2.5-1954 and earlier). This conversion is not required on Weston meters produced and Weston movie ratings published since 1956 due to the use of inherent ASA systems; However revised changes to ASA PH2.5-1960 can be taken into account when comparing with newer ASA or ISO values.
General Electric
Prior to the formation of ASA scale and similar to Weston movie speed ratings other manufacturers of photo-electric displaying, General Electric, developed their own rating system called the value of General Electric movies (often abbreviated as GE > or GE ) around 1937.
The film speed values ​​for use with their meters are published in the General Electric Film Values ​​brochure updated periodically and in the General Data Book of Electrical .
General Electric switched to an ASA scale in 1946. Meters manufactured since February 1946 were equipped with an ASA scale (labeled "Exposure Index") already. For some of the older meters with scales in "Film Speed" or "Film Value" (eg DW-48, DW-49 and early DW-58 and GW-68 variants), replaceable scales with ASA scale are available from the manufacturer. The company continues to publish the recommended movie value after that date, but then they are aligned with the ASA scale.
ASA
Based on previous research conducted by Loyd Ancile Jones (1884-1954) Kodak and inspired by the Weston movie speed rating system and the value of the film General Electric, the American Standards Association (now called ANSI) defines a new method for determining and determining film speeds of negative black- white in 1943. ASA Z38.2.1-1943 was revised in 1946 and 1947 before the standard grew into ASA PH2.5-1954. Initially, ASA values ​​are often referred to as the standard American speed number or ASA exposure index number . (See also: Exposure Index (EI).)
The ASA scale is a linear scale, ie a film that otherwise has a film speed of 200 ASA two times faster than a film with 100 ASA.
The ASA standard underwent a major revision in 1960 with ASA PH2.5-1960, when methods for determining enhanced film speed and previously applied safety factors against lack of exposure were ignored, effectively doubling the nominal speed of many black and white negative films. For example, an Ilford HP3 that has been assessed at 200 ASA before 1960 is labeled 400 ASA after that without changes to the emulsion. Similar changes were applied to the DIN system with DIN 4512: 1961-10 and BS systems with BS 1380: 1963 in subsequent years.
In addition to the defined arithmetic speed scale, ASA PH2.5-1960 also introduces a logarithmic ASA class (100 ASA = 5 Â ° ASA), where the difference of 1 Â ° ASA represents full exposure and therefore the film speed doubling. For a while, ASA values ​​are also printed on the movie box, and they see life in the form of APEX velocity value S v (without the degree symbol) as well.
ASA PH2.5-1960 was revised as ANSI PH2.5-1979, without logarithmic velocity, and subsequently replaced by NAPM IT2.5-1986 of the National Association of Photographic Manufacturers, which represents the US adoption of the international standard ISO 6 The latest issue of ANSI/NAPM IT2.5 was published in 1993.
The standard for color negative films was introduced as ASA PH2.27-1965 and saw a series of revisions in 1971, 1976, 1979 and 1981, before finally becoming ANSI IT2.27-1988 before withdrawal.
The speed of the color reversing film is defined in ANSI PH2.21-1983, which was revised in 1989 before becoming ANSI/NAPM IT2.21 in 1994, US adoption of the ISO 2240 standard.
At the international level, the ASA system was replaced by the ISO film speed system between 1982 and 1987, however, the scale of ASA arithmetic speed continues to live as a linear velocity value of the ISO system.
GOST
GOST (Cyrillic: ???? ) is scale arithmetic film speeds specified in GOST 2817-45 and GOST 2817-50. It was used in the former Soviet Union since October 1951, replacing Hurter & amp; Driffield Number (H & amp; D, Cyrillic: ???), which has been used since 1928.
GOST 2817-50 is similar to the ASA standard, which is based on the velocity point at a density of 0.2 above the base plus fog, compared to 0.1 ASA. The GOST marks are only found on pre-1987 photography equipment (films, cameras, lightmeters, etc.) from Soviet manufacturing.
On January 1, 1987, the GOST scale was adjusted to the ISO scale with GOST 10691-84,
It evolved into several parts including GOST 10691.6-88 and GOST 10691.5-88, both of which became functional on 1 January 1991.
Current system: ISO
Standard film speeds of ASA and DIN have been incorporated into ISO standards since 1974.
The current International Standard for measuring the speed of color negative films is ISO 5800: 2001 (first published in 1979, revised in November 1987) from the International Organization for Standardization (ISO). The standards relating to ISO 6: 1993 (first published in 1974) and ISO 2240: 2003 (first published in July 1982, revised in September 1994, and corrected in October 2003) determine the scale for black and white negative film speed and reversal color film, respectively.
Determination of ISO speed with digital camera is described in ISO 12232: 2006 (first published in August 1998, revised in April 2006, and corrected in October 2006).
The ISO system defines both arithmetic and logarithmic scales. The ISO arithmetic scale conforms to the arithmetic ASA system, in which the doubling of film sensitivity is represented by the doubling of numeric film speed values. In a logarithmic ISO scale, which corresponds to the DIN scale, adding 3 Â ° to a numerical value is twice that of sensitivity. For example, films rated ISO 200/24 ​​â € <â € <â € Generally, logarithmic velocities are removed; for example, "ISO 100" denotes "ISO 100/21Ã, Â °", while the logarithmic ISO speed is written as "ISO 21Ã, Â °" as per the standard. Conversion between the current scale
Let's think that arithmetic S should be that logosite logarithmic S Ã, Â ° diberikan oleh
dan membulatkan ke bilangan bulat terdekat; log adalah basis 10. It should be noted that logarithmic is a keen arithmetic diberic oleh
and rounded to the nearest standard arithmetic speed in Table 1 below.
Note table:
- The speed displayed in bold under APEX, ISO, and ASA is the actual value set in the speed standard of the relevant agency; the other value is the calculated extension for the defined speed using the same progression as for the specified speed.
- APEX S v values ​​1 to 10 correspond to the logarithmic ASA values ​​of 1 Â ° to 10 Â ° found in ASA PH2.5-1960.
- The ASA arithmetic speed of 4 to 5 is taken from ANSI PH2.21-1979 (Table 1, page 8).
- The arithmetic speed of ASA from 6 to 3200 is taken from ANSI PH2.5-1979 (Table 1, p.Ã, 5) and ANSI PH2.27-1979.
- ISO arithmetic speeds from 4 to 3200 are taken from ISO 5800: 1987 (Table "ISO speed scale", p.Ã, 4).
- The ISO arithmetic speed from 6 to 10000 is taken from ISO 12232: 1998 (Table 1, page 9).
- ISO 12232: 1998 does not specify a velocity greater than 10000. However, the upper limit for <10000 noise is given as 12500, indicating that the ISO may have envisaged a development of 12500 , 25000, 50000, and 100000, similar to 1250 to 10000. This is consistent with ASA PH2.12-1961. For digital cameras, Nikon, Canon, Sony, Pentax, and Fujifilm seem to prefer to express greater velocity in the precise power-of-2 than the previously realized high speed (6400) rather than rounding to an extension of existing developments.
- Most modern 35 mm SLRs films support automatic film speed ranges from ISO 25/15Ã,  ° to 5000/38Ã, ° with DX-coded film, or ISO 6/9Ã,  ° to 6400/39Ã,  ° manually (without exploiting lighting) compensation). Movie speed range with support for smaller TTL flash, usually ISO 12/12Ã,  ° up to 3200/36Ã,  ° or less.
- Accessory Booster for Canon Pellix QL (1965) and Canon FT QL (1966) support film speeds from 25 to 12800 ASA.
- The Canon A-1 (1978) quick movie button supports a range of speeds from 6 to 12800 ASA (but is already called ISO film speed in the manual). On exposure compensation of this camera and extreme movie speed is exclusive. Leica R8 (1996) and R9 (2002) officially support film speeds of 8000/40Ã,  °, 10000/41Ã,  ° and 12800/42Ã,  ° (in the case of R8) or 12500/42Ã,  ° (in this case) of R9), and using the exposure compensation  ± EV, the range can be extended from ISO 0.8/0  ° to ISO 100000/51  ° in half-step exposure.
- The digital camera manufacturer's arithmetic speed from 12800 to 409600 comes from the specifications by Nikon (12800, 25600, 51200, 102400 in 2009, 204800 in 2012, 409600 in 2014), Canon (12800, 25600, 51200, 102400 on in 2009, 204800 in 2011, 4000000 by 2015), Sony (12800 in 2009, 25600 in 2010, 409600 in 2014), Pentax (12800, 25600, 51200 in 2010, 102400, 204800 in 2014) and Fujifilm (12800 in 2011).
Historical ASA and DIN conversions
As discussed in the ASA and DIN sections, the definition of ASA and DIN scales changed several times in the 1950s to early 1960s so it was necessary to convert between different scales. Because the ISO system incorporates newer ASA and DIN definitions, this conversion is also required when comparing older ASA and DIN scales to ISO scaling.
The image shows the conversion of ASA/DIN in a 1952 photography book where 21/10Ã, Â ° DIN was transformed into ASA 80 instead of ASA 100.
Some classic camera exposure guides show old conversations as valid at the time of production, such as Tessina classic camera exposure guides (since 1957), where 21/10 Â ° DIN is associated with ASA 80, 18 Â ° DIN to ASAÃ, 40, etc. The classic camera user, who does not know his historical background, may be confused.
Specify movie speed
The film speed is found from the optical density plot vs exposure log for the film, known as the curve of D -log H or the Hurter-Driffield curve. Usually there are five areas on the curve: the base of fog, toes, linear region, shoulders, and areas that are too bright. For negative black-and-white films, the "speed point" m is the point on the curve where the density exceeds the base of the fog density by 0.1 when the negative is developed so that point n where the log of exposure is 1.3 units is greater. of exposure at point m has a density greater than 0.8 density at point m. Exposure H m , in lux-s, is that for point m when the specified contrast conditions are met. The speed of ISO arithmetic is determined from:
This value is then rounded to the nearest standard speed in Table 1 of ISO 6: 1993.
Determine the speed for negative color films similar in concept but more complex because it involves a separate curve for blue, green, and red. The film is processed according to the recommendation of the filmmaker rather than to the specified contrast. The ISO speed for the color reversal film is determined from the center of the curve threshold; it again involves a separate curve for blue, green, and red, and the film is processed according to the recommendation of the film manufacturer.
Applying movie speed
The film speed is used in the lighting expression to find the appropriate lighting parameters. Four variables are available for photographers to get the desired effect: lighting, film speed, f-number (aperture size), and shutter speed (lighting time). The equation can be expressed as a ratio, or, by taking the logarithm (basis 2) from both sides, by addition, using the APEX system, where each increment 1 is the multiplication of the exposure; This increase is commonly known as "stop". F-number is effectively proportional to the ratio between the focal length of the lens and the diameter of the opening, the diameter itself is proportional to the square root of the aperture area. Thus, the lens set to f /1.4 allows twice as much light to attack the focal plane as the lens assigned to f /2. Therefore, any factor f -number of the square root of two (about 1.4) also stops, so the lens is usually marked in that development: f /1.4, 2, 2.8, 4, 5.6, 8, 11, 16 , 22, 32, etc.
The ISO arithmetic speed has properties that are useful for photographers without equipment to take measurable light readings. Proper exposure will usually be achieved for bright sights in the bright sun if the lens aperture is set to f/16 and the shutter speed is the opposite of the ISO film speed (eg 1/100 sec for 100 ISO film). This is known as the bright 16 rule.
Exposure index
The exposure index, or EI, refers to the rate of speed assigned to a particular movie and shooting situation that is different from the actual film speed. This is used to compensate for the inaccuracy of equipment calibration or process variables, or to achieve certain effects. The exposure index can only be called speed setting , compared to the speed of rating .
For example, a photographer can judge an ISO 400 film on the EI 800 and then use thrust processing to obtain a printable negative under low-light conditions. The film has been exhibited on the EI 800.
Another example occurs where camera shutter is incorrectly calibrated and consistently exposes or overrides the movie; likewise, the light meter may not be accurate. One can adjust the EI rating accordingly to compensate for this defect and consistently produce negatively exposed correctly.
Maps Film speed
Reciprocity
After exposure, the amount of light energy reaching the film determines the effect on the emulsion. If the brightness of the light is multiplied by the factor and the film exposure decreases by the same factor by varying the shutter speed and camera aperture, so that the received energy is the same, the film will be developed to the same density. This rule is called reciprocity. The system for determining the sensitivity to the emulsion is possible because reciprocating holds. In practice, reciprocity works well enough for normal photographic films for the exposure range between 1/1000 seconds to 1/2 second. However, this relationship is broken beyond these limits, a phenomenon known as mutual failure.
Film sensitivity and grain
The size of the silver halide grains in the emulsion affects the sensitivity of the film, which is associated with granularity because larger grains give the film a greater sensitivity to light. Fine-grain films, such as films designed to photograph or copy original negative cameras, are relatively insensitive, or "slow", as they require brighter light or longer exposure than "fast" movies. Fast film, used for shooting in low light or capturing high speed motion, produces relatively coarse images.
Kodak has defined the "Print Grain Index" (PGI) to characterize film grains (only negative films), based on granular differences only seen in the mold. They also defined "granularity", grain measurements using RMS measurements of density fluctuations in uniformly exposed films, measured by microsensitometer with 48 micrometers of aperture. Granularity varies with exposure - less bright films look more mottled than films that are too bright.
Marketing anomalies
Some high-speed black-and-white films, such as the Ilford Delta 3200 and Kodak T-MAXÃ, P3200, are marketed at film speeds exceeding the actual ISO speed as determined by ISO testing methods. According to each data sheet, Ilford's product is actually an ISO 1000 film, while Kodak's film speed is 800 to 1000 ISO. The manufacturer does not indicate that the number 3200 is the ISO rating on the packaging. Kodak and Fuji also market E6 films designed to drive (hence the prefix "P"), such as Ektachrome P800/1600 and Fujichrome P1600, both at ISO 400 base speeds.
Digital camera ISO speed and exposure index
In a digital camera system, an arbitrary relationship between the exposure and the value of the sensor data can be achieved by adjusting the sensor signal strengthening. The relationship between the sensor data value and the finished image brightness is also arbitrary, depending on the parameters selected for the interpretation of the sensor data into the image color space such as sRGB.
For digital photo cameras ("digital photo cameras"), the exposure index rating (EI) - usually called the ISO setting - is determined by the manufacturer in such a way that the sRGB image files generated by the camera will have light similar to what will be obtained with the film from the same EI rating at the same exposure. The usual design is that the camera parameters for interpreting sensor data values ​​to sRGB values ​​are set, and a number of different EI options are accommodated by varying the sensor signal gain in the analog world, before conversion to digital. Some camera designs provide at least some EI options by adjusting the signal amplification sensors in the digital world. Some camera designs also provide EI adjustments via optional lightening parameters for interpretation of sensor data values ​​to sRGB; this variation allows different sacrifices between the range of spotlight that can be captured and the number of sounds introduced into the image shadow area.
The digital camera has far surpassed the film in terms of sensitivity to light, with speeds equivalent to ISO to 4,560,000, an unexpected figure in the field of conventional film photography. Faster processors, as well as advancements in noise reduction techniques, allow this type of processing to be executed when photos are taken, allowing photographers to store images that have higher repair rates and will be time consuming to process earlier. generation of digital camera hardware.
ISO 12232: 2006 standard
ISO standard ISO 12232: 2006 gives digital camera manufacturers a choice of five different techniques to rank exposure index on any sensitivity settings provided by certain camera models. Three techniques in ISO 12232: 2006 were brought from the standard version of 1998, while two new techniques that enable the measurement of JPEG output files were introduced from CIPA DC-004. Depending on the technique chosen, the exposure index rating may depend on the sensitivity of the sensor, the sensor noise, and the resulting image display. The standard sets the light sensitivity measurements of the entire digital camera system and not from individual components such as digital sensors, although Kodak has reported using variations to characterize the sensitivity of two sensors in 2001.
The Exposure Index (REI) Exposure Technique (REI), new in the 2006 version of the standard, allows manufacturers to make arbitrary selections of camera model EI. The choice is based solely on the manufacturer's opinion of what value of EI produces sRGB images that are well exposed to various sensor sensitivity settings. This is the only technique available below the standard for output format that is not in the sRGB color space. This is also the only technique available below the standard when multi-zone metering (also called pattern metering) is used.
The Standard Output Sensitivity (SOS) technique, also new in the 2006 version of the standard, effectively establishes that the average level in the sRGB image should be 18% gray plus or minus 1/3 stop when exposure controlled by an automatic exposure control system calibrated per ISO 2721 and set to EI without exposure compensation. Since the output level is measured in the sRGB output of the camera, it applies only to sRGB images - usually JPEG - and not to display files in raw image format. This does not apply when multi-zone measurements are used.
The DC-004 CIPA standard requires that Japanese digital camera manufacturers use REI or SOS techniques, and DC-008 updates the Exif specification to distinguish between these values. As a result, three IE techniques carried from ISO 12232: 1998 are not widely used in recent camera models (around 2007 and beyond). Because previous techniques do not allow measurements of images produced with lossy compression, they can not be used at all on cameras that produce images only in JPEG format.
The saturation-based technique (SAT or S sat ) is closely related to the SOS technique, with the sRGB output level measured at 100% white rather than 18% gray. The SOS value is effectively 0.704 times the saturation-based value. Since the output level is measured in the sRGB output of the camera, it applies only to sRGB images - usually TIFF - and not to display files in raw image format. This does not apply when multi-zone measurements are used.
Both noise-based techniques are rarely used for consumer digital cameras. These techniques determine the highest EI that can be used while still providing "very good" or "useable" images depending on the technique chosen.
Measurements and calculations
The ISO speed rating of a digital camera is based on the sensor and image processing properties performed in the camera, and expressed in a luminous exposure H (in seconds lux) arrives at the sensor. For typical camera lenses with an effective focal length f that is much smaller than the distance between the camera and the photographed scene, H is given by
di L adalah luminansi adegan (dalam candela per m²), t adalah waktu pencahayaan (dalam detik), N adalah aperture f-number, dan
is the factor dependent on the transmittance of the lens, the vignetting factor v v (? ), and the angle ? relative to the lens axis. Typical values ​​are q Ã, = Ã, 0.65, by ? Ã, = Ã, 10Ã, Â °, T Ã, = 0,9, and v Ã, = Ã, 0,98.
Speed ​​based on saturation
Kecepatan saturation-based didefinisikan sebagai
di mana adalah eksposur máximo yang mungkin yang tidak mengarah that output kamera yang terpotong atau mekar. Biasanya, batas bawah kecepat saturasi ditentukan oleh sensor itu sendiri, tetapi dengan penguatan amplifier anta sensor dan converter analog-ke-digital, kecepatur saturasi dapat ditingkatkan. Faktor 78 dipilih sedemikian rupa sehingga pengaturan eksposur berdasarkan pada light meter standar dan permukaan reflektif 18 persen akan menghasilkan gambar dengan tingkat kelabu 18%/? 2 = 12.7% saturation. Faktor ? 2 menunjukkan bahwa ada setengah stop headroom untuk menangani refleksi spekuler yang akan tampak lebih terang dari 100% yang mencerminkan permukaan putih.
Kecepatan berbasis noise
The noise-based speed is defined as the exposure that will cause a certain signal-to-noise ratio on individual pixels. Two ratios are used, 40: 1 ("excellent image quality") and 10: 1 ratio ("acceptable image quality"). This ratio is subjectively determined based on a resolution of 70 pixels per cm (178 DPI) when viewed at a distance of 25 cm (9.8 inches). The signal-to-noise ratio is defined as the standard deviation of the weighted average of luminance and individual pixel color. The noise-based speed is largely determined by the sensor properties and is somewhat affected by noise in the electronic gain and AD converter.
Standard output sensitivity (SOS)
Selain peringkat kecepatan di atas, standar juga mendefinisikan sensitivitas output standar (SOS), bagaimana pemaparan terkait dengan nilai piksel digital dalam gambar output. Ini didefinisikan sebagai
di mana adalah eksposur yang akan mengarah ke nilai 118 dalam piksel 8-bit, yang merupakan 18 persen dari nilai saturasi dalam gambar yang dikodekan sebagai sRGB atau dengan gammaÃ, = 2.2.
Diskusi
The standard determines how speed ratings should be reported by the camera. If noise-based speeds (40: 1) are higher than saturation-based speeds, noise-based speeds should be reported, rounded down to standard values ​​(eg 200, 250, 320, or 400). The reason is that exposure according to speed based on lower saturation will not produce a better looking image. In addition, exposure latitude can be determined, from saturation-based speeds to 10: 1 noise-based speeds. If noise-based speeds (40: 1) are lower than saturation-based speeds, or are undefined because of high noise , saturation-based speed is determined, rounded up to the default value, because using noise-based speed will cause the image too bright. The camera can also report SOS-based speed (explicitly as SOS speed), rounded to the nearest standard speed rating.
Misalnya, mungkin camera sensor memiliki properti berikut: , , give . Menurut standar, camera harus melaporkan sensitivitasnya sebagai
- ISO 100 (siang hari)
- ISO kecepatan lintang 50-1600
- ISO 100 (SOS, siang hari) .
Peringkat SOS dapat dikendalikan oleh pengguna. Untuk kamera yang berbeda dengan sensor berisik, properti mungkin , , give . Dalam hal ini, camera harus melaporkan
- ISO 200 (siang hari) ,
as well as user customizable SOS values. In all cases, the camera must indicate the white balance setting for which the speed rating applies, such as daylight or tungsten (incandescent).
Despite this detailed standard definition, the camera usually does not clearly indicate whether the "ISO" user setting refers to noise-based speed, saturation-based speed, or specified output sensitivity, or even some number created for marketing purposes. Since the 1998 version of ISO 12232 does not permit the measurement of camera outputs that have lossy compression, it is not possible to properly apply one of these measurements to a camera that does not produce sRGB files in an uncompressed format such as TIFF. After the publication of CIPA DC-004 in 2006, Japanese digital camera manufacturers were still asked to determine whether the sensitivity rating of REI or SOS.
As should be clear from above, the larger SOS settings for a given sensor come with some loss of picture quality, as is the case with analog movies. However, this loss is seen as image noise rather than grain. Currently (January 2010) APS and 35mm digital image sensors, both CMOS and CCD-based, do not produce significant sound until approximately ISO 1600 .
See also
- Frame speed
- The lens speed
- Selected number
References
Further reading
External links
- What does ISO mean for digital cameras? Digital Photography FAQ
- Modeling, estimating and deleting a signal-dependent sound for digital imaging sensors
Source of the article : Wikipedia
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