Photographic Glossary-H

H&D curve
Another name for the D/log E curve, after its originators, Ferdinand Hurter and Vero C. Driffield.

Halation
Is a diffused ring of light typically formed around small brilliant highlight areas in the subject. It is caused by light passing straight through the emulsion and being reflected back by the film base on the light sensitive layer. This records slightly out of register with the original image. The production of "halos" round bright spots in an image, by light reflecting from the back of the film-base. General film bases are given a light absorbing coat the anti-halation back to prevent this.

Halftone image
An image reproduced through a special screen made up of dots of various sizes to simulate shade of gray in a photograph. Typically used for newspaper or magazine reproduction of images.

Halftone screen
A pattern of dots of different sizes used to simulate a continuous tone photograph, either in colour or black and white.

Halo
A light line around object edges in a image, produced by the USM (sharpening) technique.

Handle Mount flash
Also often referred as bracket flash. It comprised of one arm of the L-shaped bracket extends under the camera body and uses the camera's tripod socket to mount the camera on the bracket. The vertical arm of the bracket serves as a handle and mounts a flash unit in an accessory shoe often on top of the handle portion, but there are other methods. Flash mounted in a bracket usually requires a separate electrical cord to make the electrical connection between camera body and flash unit.

Hanger
A frame for holding sheet film during processing in a tank.

Hard copy
Refers to a print or proof, as opposes to viewing on a monitor.

Hard drive
A built-in or off-line fixed storage medium which holds large amounts of data that can be accessed rapidly depending on the power of the computer.

Hard proof
A printed proof of an image or document, intended to accurately convey colour. Contrast with soft proof.

Hardeners
Are chemicals often used with a fixing bath to strengthen the physical characteristics of an emulsion. The most common hardeners are potassium or chrome alum.

Header
Technical information packaged with an image file, which may be of use in displaying the image (e.g., length and width in pixels), identifying the image (e.g., name or source), or identifying the owner.

H-Format
One of the three selectable Advanced Photo System print formats; identical to the 9:16 aspect ratio used in high-definition television (HDTV); suitable for wider shots than usual, such as groups; produces prints of 3.5 x 6 inches or 4 x 7 inches

Hi 8
Video recording format, also refer a High Band 8mm format.

High contrast
A wide range of density in a print or negative.

High key
A light image that is intentionally lacking in shadow detail.

High-bit
An RGB system or image containing more than 24 bits of colour data per pixel.

Highlights
Small, very bright part of image or object. Highlights should generally be pure white, although the term is sometimes used to describe the lightest tones of a picture, which, in that case, may need to contain some detail.

Highlights
The whitest or brightest part of an image; the opposite of shadows.

Histogram
A graphic representation of how brightness and darkness pixels are distributed in an image. A histogram skewed heavily to the left indicates a dark image, while a histogram skewed to the right indicates a light image.

History palette
The history palette lists the actions that have been done to an image and allows you to step forward or backward to a certain point.

HMI Lighting
Halide Metal Iodine lighting uses special bulbs and power supplies to produce flicker free lighting. This is useful when using slow digital scanning backs for Large Format cameras. These scanning backs would take a few seconds for exposure, during that time period the lights must remain flicker free to produce even illumination and constant exposure through out the scan. Hot lights could not provide such a task.

Honeycomb
Grid which makes light from a flash (or other source) more directional, like a spot rather than a flood.

Horizontal Resolution
The number of vertical lines that a system is capable of producing (counted on a horizontal axis).

Host
The computer that performs centralized functions in a network.

Hot Shoe
A flash connector generally found on the top of the camera that lets you attach a flash unit and trigger it in sync with the shutter. There are two methods of firing a flash, PC cord or hotshoe. The hotshoe use, flash has a foot that connects to socket on top of the camera which contains the contacts needed to fire the flash. Hotshoe flashes can be used on a flash bracket with the aid of a off camera cord which simply acts as an extensions of the camera's hotshoe.

Hot Shoe
Usually rest around the pentaprism of the camera (but some were designed around the film rewind knob). It has an electrical contact which mated with a contact in the mounting foot of the flash unit. This allows the camera to fire the flash at the proper time without any other electrical connections between flash and camera. The fitting on a camera that holds a small portable flash. It has an electrical contact that aligns with the contact on the flash unit's "foot" and fires the flash when you press the shutter release. This direct flash-to-camera contact eliminates the need for a PC cord. Some referred it as accessory shoe. Modern flash demand more than just the main electrical contact and often has more dedicated functions such as TTL control, viewfinder ready light etc. and thus, you will find more secondary contacts other than the main.

Hotlight
Unlike a strobe which provides a quick burst of light, a hotlight is constantly on and does not strobe. Because these lights are always on, metering becomes much easier and a flash meter is not necessary. The disadvantage of hot lights is just as they sound, they produce a lot of heat because of the intensity of the light.

Hot-spot
Concentration of light in a particular area.

HSB The hue, saturation. brightness colour model.

HSL
Hue, Saturation, and Lightness. A method of describing any colour as a triplet of real values. The hue represents the colour or wavelength of the colour. It is sometimes called tone and is what most people think of as colour. The hue is taken from the standard colour wheel and is thus calibrated in degrees about the wheel. Saturation is the depth of the colour. It states how gray the colour is. It is real valued parameter from 0.0 to 1.0 with 0.0 indicating full gray and 1.0 representing pure hue. The lightness is how black or white a colour is. It also ranges from 0.0 to 1.0 but with 0.0 representing black and 1.0 white. A lightness of 0.5 is pure hue.

HTML
Hypertext Markup Language. An encoding format for identifying and linking electronic documents used to deliver information on the World Wide Web.

Hue error
The degree of contamination in a process colour ink or other pigments that alters its appearance from that of a perfect process colour. For example most magenta inks are contaminated with yellow, making them appear to be red, rather than purplish-red.

Hue
The aspect of colour that distinguished it from another colour (what makes a colour red, green, or blue). Hue is distinct from saturation, which measures the intensity of the hue.

Hybrid Imaging
Electronic imaging systems that mix traditional silver-halide technologies with digital imaging technologies.

Hydroquinone
A developing agent, also know as Quinol.

Hyperfocal Distance
Distance of the nearest object in a scene that is acceptably sharp when the lens is focused on infinity. The distance to the nearest plane of depth of field ( the nearest object in focus) when the lens is focused on infinity. Also the distance to the plane of sharpest focus when infinity is at the farthest plane of the depth of field. Focusing on the hyperfocal distance extends the depth of field from half the hyperfocal distance to infinity. The point at which the maximum depth of field exists. At any given aperture, the depth of field extends twice as far behind the point of focus as in front of this same point. In order to have the greatest possible sharpness through out as much of the scene as possible, focusing at the hyperfocal point is necessary. To do this, the lens must have a focusing window which contains info on the distance which the lens is focused, as well as aperture settings. If the object you are focusing on is at infinity, simply note which aperture is being used, lets assume f/22. Simply focus on the object, then rotate the focusing ring such that the infinity now lies at the f/22 mark on the focusing window. If however, you were focusing on a tree which was 50' away (by reading the focusing window, again, simply rotate the focusing ring such that 50 is now located over f/22, assuming the use of f/22.

Hyperlinks
Typically text, but also graphics, that serve as links that let you move around on the Internet and connect to different web sites. Hyperlinks are usually blue and underlined.

Hypo
A common name for any fixer; from the abbreviation for sodium hyposulfite, the previous name for sodium thiosulfate (the active ingredient in most fixers).

Hz
An abbreviation for hertz-an international unit of frequency which equals one cycle per second.