Infrared photography – Wikipedia

Infrared image of the Mississippi river, crossed by a bridge and a dam, between leaves on the left (in red) and construction areas on the right (in blue).

In infrared photography , the film or the photographic sensor used are sensitive to infrared light. The part of the capture captured is actually the Near infrared , with a wavelength of 700 to around 900 nm (close to the visible spectrum), different from the distant infrared , used for thermal imagery. An infrared filter is usually added to the camera, to filter visible light and only let the infrared light pass (these filters therefore seem black, or very dark red).

The images obtained are in false colors or in black and white, of a dreamlike appearance thanks to the leaves and herbs which seem to be glowing or white like snow. This appearance is called Wood effect , named after the pioneer of the Robert W. Wood shooting type ^{[ Note 1 ]} . The skies appear black, from which the clouds which remain very white stand out clearly. Finally, the infrared portraits show milky skin, as well as often black eyes.

Until the 1900s, infrared photography was impossible because of the silver halogenure emulsions which were not sensitive to these radiation ^{[ first ]} . The first infrared photos were published in the edition of October 1910 of the Journal of the Royal Photographic Society, illustrating an article by Robert W. Wood, the pioneer who gave his name to the Wood effect ^{[ 2 ]} . The centenary of this event will also be co -organized by the RPS in 2010 ^{[ 3 ]} . As Wood’s photographs were made with a film that required very long exhibition periods, most of his shots concerned landscapes. Some of Wood’s photographs made in Italy in 1911 were made on plates provided by Kenneth Mees of Wratten & Wainwright. Mees took some infrared photos in Portugal in 1910, which are now kept in the Kodak archives. Photographic plates and taints sensitive to infrared were produced in the United States during the First World War, to improve the quality of aerial photographs (which were less embarrassed by mists) ^{[ 4 ]} . After 1930, manufacturers, including Kodak, provided emulsions used for infrared astronomy ^{[ 5 ]} .

Kodak, 1935, A.W. Stevens

It was during the 1930s, with the provision of the first usable film, that the infrared photo became accessible to the public. In 1937, 33 different films were available on the market, produced by five manufacturers, including Agfa, Kodak and Irford ^{[ 6 ]} .
Scenes of American night movies were filmed with this kind of dandruff, as in the night air stages in the film Engaged against reimbursement by James Cagney and Bette Davis ^{[ 7 ]} . In the 1940s, Kodak developed the Aero-Reversal Kodacolor film; It was the first version of the series Ektachrome infrared aero film which broadcast the infrared photo technique in false colors. This film was produced in 35 mm in the 1960s, up to the Kodak Aerochromme III Infrared Film 1443 version.

Popularity in the sixties [ modifier | Modifier and code ]

An infrared photo of a train from the Ringling Brothers Cirque (Cambridge, Massachusetts).

The infrared photo became really popular in the 1960s, when several artists used it: Jimi Hendrix, Donovan, Frank Zappa and Grateful Dead used all this kind of photo for the cover of one of their albums. Jean-Louis Swiners tried for Realities , not conclusive and unpublished. The strange colors and effects of these photographs are well framed with the aesthetics of the psychedelic wave which appeared then. If for some, this technique is only a simple process, certain artists like Elio Ciol used it as derivative of black and white.

With the appearance of digital photography, the infrared photo is gaining popularity. It is sold as a work of art in the galleries.

A peculiarity of the infrared photo is due to the development: the focus of infrared light is offset from the visible light because of its different wavelength ^{[ 8 ]} ; The development must therefore be offset. If most of the objectives with manual focus for 35 mm or medium format SLRs had a specific focus benchmark (a point, a line, a diamond, often accompanied by the letter ‘r’), the autofocus objectives recents no longer have it. The difficulty is that autofocus cannot work since they are blinded by the filter. It is therefore necessary to place the device on tripod, take stock manually, then screw the filter to take the photo. In the absence of a focus benchmark, it is better to close the diaphragm to maximize the depth of field and avoid fuzzy subjects (on the other hand, the diffraction problems prevent closing beyond f/16 or f/22 ). The focus benchmarks for infrared depend in part on the filter and the film used, it is therefore necessary to do tests anyway. Only modern apochromatic objectives (APO) are not sensitive to this discrepancy ^{[ 8 ]} . Finally, the objectives are calculated to be optimal in the face of visible light, are then less well suited to the wavelengths of the infrared. Consequently, the quality of an infrared photo will be lower than that of a photo on the visible spectrum ^{[ 8 ]} .

Most conventional cameras can be used for the photo Near infrared . The infrared shooting distant from the visible spectrum, called thermography, requires specific equipment.

With patience and ingenuity, most dandruff can be used ^{[Ref. necessary]} . On the other hand, some boxes of the 1990s, which use infrared sensors to identify the film’s training holes, can veil the negatives.

Black and white dandruff [ modifier | Modifier and code ]

Infrared black and white dandruff are sensitive to wavelengths between 700 and 900 nm (near infrared spectrum), and for the most part, in blue light. This type of film requires specific development times, but with the same products as normal dandruff.

Photos with negative infrared films are very similar to those taken with classic dandruff, because blue light prints the film in a way that hides the effects of infrared light. Filters are therefore used to remove the wavelengths corresponding to blue, such as orange (15 or 21) or red (23 or 25) filters let a part of blue light pass, dark red filters (29) very little, And the opaque filters (72) let the wavelength corresponding to the infrared.

Some film, such as the Kodak High Speed ​​Infrared (HIE) black-and-white , showed a bright halo in the photos. This effect is not due to any characteristic of infrared films, but to a problem with the design of some of them: they did not have an anti-halo layer, which prevents light from crossing the film, rebounds on the Box and is again printed on film, forming a halo. For the same reasons, these must be loaded and discharged in total darkness.

In November 2007 , Kodak announces the cessation of the production of HIE 35s mm , for reasons of cost ^{[ 9 ]} .

Color dandruff [ modifier | Modifier and code ]

Example of color infrared photo.

The reverse color dandruff (slideshow) have three sensitive layers, two of which capturing the green and red lights, the third capturing the infrared. However, the green layer is also sensitive to blue light, they must be used with a yellow or orange filter to avoid too bluish rendering. By means of what, green light will appear in blue in the image, red light in green, and the close infrared in red. The chlorophyllian activity of foliage can be deducted from their dominance in green and infrared in the photo ^{[ ten ]} , indicating its stage of development or its health condition.

The first film had to be developed with the E-4 treatment, but Kodak then developed a developable film with classic E-6 products, although the best results were obtained with the AR-5 processing process. In general, these dandruffs did not ask to use a quirky development for infrared, nor to be discharged in the dark.

Kodak announced the end of the production of the Ektachrome Professional Infrared (EIR) 35 mm , for reasons of cost.

Example of colorless infrared photography in color, with the inversion of the channels and taken with a device whose anti-infrared filter of the sensor has been dismantled.

Another example of digital infrared photography, without inversion of channels.

The sensors of digital devices are of sensitive origin to infrared light ^{[ 11 ]} , which would pose a problem in normal use since the autofocus would be disrupted, and the red colors supersaturated. The sensors are therefore surmounted by a filter which blocks infrared, which makes these devices difficult to use for the IR photo: very long breaks are necessary, which causes digital noise or blurring. Certain objectives, because of their multilayer treatment optimized for visible light, create a halo in the center of the photo.

A Nikau palm against a background of blue sky: this strong contrast is typical of the IR photo outdoors.

A technique is therefore to dismantle the infrared filter; The shooting is then normally done, with the exception of the output of the focus. In this case, the halo caused by certain objectives disappears. The blue and green photosites of the sensors continuing to operate, it is possible to obtain color images. The few boxes using Foveon X3 sensors, less protected against IRs, are more easily usable. The Sigma SD14, is a special case, since its anti-IR filter is mounted in front of the mirror, and is removable and very easily reassembled ^{[ twelfth ]} . ONE phase markets digital backs (means formats) sensitive to IR. It is usual to add a filter that blocks visible light (to keep only the infrared), but it is possible to do without it, to enjoy a mixture of natural colors and the Wood effect. Driver can also be used as a DIY filter ^{[ 13 ]} . Sony has marketed two aircraft, the DSC-F717 and DSC-F828, whose infrared filter in front of the sensor could rotate, allowing to take infrared photos.

On the other hand, there is no method to obtain an infrared color image directly as we obtained in argentic. The only solution is to make two shots, one in color, the other in infrared, and then mix them in post-processing (by replacing the red channel of the color photo with the infrared photo).

Fuji produced cameras for criminal or medical purposes that do not have an anti-IR filter. The first, the S3 Pro Uvir, also had a sensitivity to ultraviolet. Was also marketed the IS-1, a non-reflex device derived from the Finepix S9100, without sensitivity to ultraviolet. In 2007, Fuji presented a new version based on the Nikon D200/Fujifilm S5 called the IS Pro. These models are reserved for sales for professionals, who must commit to not using them “for purposes contrary to ethics” ^{[ 14 ]} .

In astronomy, it is interesting to capture the Hα line (656.3 nm) that the human eye perceives as a pure red. However, as the eye is less sensitive to these radiation than in the orange, around 600 nm, the anti-infrared filter equipping a standard digital box also strongly reduces this color. To take this problem into account, the Canon manufacturer has made a “astronomy” version for some of its reflex boxes in which the filtering of the deep red and the close infrared has been attenuated ^{[ 15 ]} .

Satellite sensors and thermographic sensors are sensitive to wider wavelengths, and use technologies different from those of cameras. In particular, they are equipped with coolers, to remove radiation from the device because of its temperature.

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