Digital Photography Terminology

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If you've been baffled by digital photography terminology, I hope this glossary of terms will help.

Throughout the pages of this site, I always endeavour to be as clear and straight forward as possible but perhaps the odd piece of jargon slips through!

It therefore occurred to me that an on-tap glossary might be a big help, so here it is for you.

I'm adding to it whenever relevant terminology springs to mind.

However, if YOU would like me to explain a term or phrase then please click on the link below entitled "Digital Photography Terminology to Add?" and navigate your way to the comments.

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New! Make requests and leave comments by using the Facebook Comments feature at the bottom of the page!

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Without further ado, here is an alphabetical list of digital photography terminology for you...

ACR:

Adobe Camera Raw, a Photoshop plug-in for opening and processing image files captured using the RAW File Format.

Aperture:

1. Light travels through a camera's lens or small hole (in the case of pinhole cameras) and is focussed on either a light-sensitive digital chip, film or paper. The path through the glass lens or the small hole is known as the aperture.

   The size of the aperture is described in f-stops. For example: f2, f2.8, f4, f5.6, f8, f11, f16 and so on. The smaller the number, the bigger the opening and vice versa.

2. Image cataloging and editing software manufactured by Apple in direct competition with Adobe Photoshop Lightroom.

Aperture Priority:

A shooting mode seen on many cameras with automatic metering capabilities (most cameras in the modern era!). It usually appears as AV in a menu or on a control knob.

Aperture Priority allows the user to select the desired aperture, the camera will then automatically select the appropriate shutter speed to make the correct exposure.

Banding:

This term is often used interchangeably with posterisation (see definition below).

However, strictly speaking, it should only be used to describe a printing flaw whereby undesirable stripes are seen in a print, perhaps caused by a blocked ink cartridge or the like.

Bit Depth:

Digital image files are comprised of their smallest unit, pixels. The pixels not only have height and width but they also have depth, known as bit depth or color depth.

The depth is purely a mathematical notion; the files are not three-dimensional!

The bit depth of a digital file tells us how many grades or steps of color can be described by the pixels in that file; as the bit depth becomes higher, the colors are in effect described more accurately, as they can be described by a greater number of shades or steps.

As you can see, quite an involved topic and one I will write about in more detail soon.

Bit Depth is not to be confused with Gamut (see definition below).

Calibration:

The first stage in a two-part process to bring a color device (such as a display, camera, scanner or printer) into a neutral state ahead of profiling.

CCD:

Charge-Coupled Device, a type of light-sensitive digital chip found in many digital cameras and scanners.

Channel Chops:

A geeky piece of jargon referring to Channel Operations; the editing and compositing of files using an advanced knowledge of channels in editing programs such as Photoshop.

Channels:

Digital files are comprised of channels each describing the amount of a certain color within that channel.

Example: RGB files (see below) contain three channels (Red, Green and Blue) whilst CMYK files contain four channels (Cyan, Magenta, Yellow and Black).

Chip:

A light-sensitive chip is housed within scanners and digital cameras, capturing the light that falls or is focussed on it.

By the way, the chip doesn't store information, that's the job of a memory card or hard drive.

Chromatic Aberration:

One of the hallmarks of a high-quality lens is to focus all the wavelengths of light into the same point at any given position on a digital chip or other light-sensitive material.

If it doesn't, unsightly splitting of the wavelengths occurs and this is known as Chromatic Aberration. It usually manifests itself in areas of high-contrast, particularly at the edges and corners of photographs.

CMOS:

Complementary metal–oxide–semiconductor (well, you did ask), a type of light-sensitive digital chip found in many digital cameras.

CMYK:

Cyan, Magenta, Yellow and Black, the four colors that form the foundation of most ink-based printing processes.

In truth the 'K' isn't actually from the word 'Black'. That's just an easy way to remember it.

'K' actually refers to the Key channel.

In theory, if Cyan, Magenta and Yellow ink is mixed then black ink should result.

However, due to the impossibility of making such pure ink as to fulfill this theory, a brown sludgy mess occurs.

Therefore, the black channel is added and is the key to making a deep black actually print on paper.

Color Management:

A process used to accurately describe the color capabilities of digital devices, so that they can all be used in conjunction with one another to produce expected results.

Color Temperature:

Measured in kelvins, color temperature is a method used to describe the color of white light, to indicate whether it is warm, neutral or cool (or something else!)

Compact Flash:

A type of solid-state flash memory card for use in certain digital cameras to store the digital photographs created by the camera.

Contrast:

Of course, images tend not to be one solid color or tone.

They have a brightest point and a darkest point. Contrast is the difference between the two.

A foggy scene tends to be low in contrast and, conversely, a bright sunny scene is usually high in contrast.

DPI:

Dots Per Inch, see Resolution below.

DNG:

Short for Digital Negative, DNG is a RAW file format designed by Adobe in an effort to make digital files future-proof.

It is fast-becoming the industry standard.

Dynamic Range:

The range of tones contained within a digital file, from the deepest shadows to the brightest highlights.

Digital photographs that contain high amounts of detail in both the shadows and the highlights are said to have a High Dynamic Range, often abbreviated to HDR.

Gamut:

The total extent of tones and colors a particular digital device is capable of displaying, capturing or printing.

Giclée:

A term first coined in the Nineties to differentiate the new era of higher quality commercial inkjet printing from the cheaper, fast-fading offerings on the market at the time.

One of these days, I'll tell you the full reasons not to use this word. Maybe you can work it out in the meantime?

Put it this way, the French don't take giclée to mean inkjet...!

Grayscale:

A grayscale file is comprised of shades of gray and contains no color information—also known as a monochromatic or black and white image.

Hue:

Very simply put, hue refers to the appearance of a color.

To shift the appearance of a color, without altering its brightness or saturation, is to shift its hue (measured on a scale of 0-360 degrees).

ICC Profile:

In short, ICC Profiles are small files that give a jacket of meaning to digital photographs and digital hardware.

They act as the cover on a book, telling the user and/or a computer how to interpret the data being presented to him, her or it.

For a more complete explanation, check out my article What is an ICC Profile?

Interpolation:

There are two methods of changing the dimensions and/or size of a file: see resizing and resampling.

The latter (resampling) is also known as interpolating and describes the act of increasing the number of pixels in a file, usually in an effort to increase the linear dimensions (the width and height) and/or the resolution.

When an instruction is given to increase the file size (through Photoshop's Image Size dialog box, for example), neighbouring pixels are interpolated to create extra new pixels between them, based on data from the existing ones.

Beware: Although extra pixels are created, this almost certainly won't result in increased detail!

ISO:

In this context, ISO refers to the degree of a digital chip's apparent sensitivity to light.

The higher the ISO, the more sensitive the chip is to light falling on it.

ISO 50 is low and is therefore suited to bright conditions.

On the other hand, ISO 800 is high and suited to low-light conditions.

The term stems from 'the old days' of film when the ISO range typically ran from 25 to 3200 including 50, 64, 100, 160, 200, 400, 800 and 1600 along the way.

Each time the number doubles, the film becomes more sensitive by one stop. So, ISO 400 film is two stops more sensitive than ISO 100 film, for example.

Don't be misled in the modern era, however, as a digital chip doesn't actually become more sensitive to light. It just appears to; a result of the camera's software algorithms adjusting the appearance of the image, according to the settings chosen by the user, in a meaningful way to which we can relate.

IQ:

Image Quality

JPEG:

A digital image file format which saves data using lossy (see below) compression.

Files are usually saved as JPEGs to make them as small as possible to be viewed and/or delivered efficiently via the internet...

...or perhaps to increase the possible quota of images that can be stored on a camera's memory card.

The user can choose different quality levels in order to adjust the compromise between file size and image quality.

By the way, JPEG stands for Joint Photographic Experts Group!

Lossless:

A form of compression that doesn't discard or compromise on the quality of data stored.

The TIFF file format's LZW option is an example of lossless compression.

However, when selecting this option, the files takes longer to read and write.

Lossy:

A form of compression that discards and compromises on the quality of data stored.

The JPEG file format is an example of lossy compression.

Luminance:

Refers to the strength of light being reflected or emitted from an object.

The stronger the luminance, the brighter the object appears to be.

You will see this term crop up throughout the digital photography workflow but also when discussing and assessing prints. For example:

"The platinum prints by Frederick H. Evans have a real luminance to them."

Megapixel:

One megapixel = one million pixels when discussing a digital file.

This need to be a full-blown article as there are many things to discuss surrounding the term megapixel.

For example, megapixels are often used to describe camera resolution but you must bear in mind that pixels are the smallest unit in a digital file and the capture chip in a camera is not a digital file.

Therefore, megapixels, as far as cameras are concerned, describe the total number of image sensor elements or receptors.

There's also the question of "How many pixels is enough?", an answer that I will certainly need to answer in a dedicated page to follow very soon...!

Keep your eyes peeled, it will likely be called "What is a Megapixel?"

Micro Four Thirds:

A camera design and format built from the ground up, entirely with digital technology in mind (as opposed to adapting existing film equipment).

Manufacturers claim that this results in fittings and optics being better-optimised to the digital chips capturing the data.

Panasonic and Olympus are currently the forerunners in this arena, producing beautiful cameras that certainly pack a punch in terms of ergonomics and image quality.

Monochromatic:

Meaning "constructed of one color", this term is often used to describe greyscale (black and white) images.

However, it's worth noting that if an image is entirely constructed of light and dark tones of one shade of red, for example, then that is also a monochromatic image!

Panchromatic:

A panchromatic capture or response is one that is sensitive to all wavelengths of light.

Therefore all visible colors are captured in a way that looks natural to the human eye.

Pixel:

The smallest unit of a digital image file.

A pixel can vary in size but you can't have anything less than one pixel!

Plug-in:

A piece of software designed to work seamlessly within another, usually larger, piece of software.

For example, there are plug-ins galore for Photoshop and Lightroom, all of which are designed to increase and improve the functionality of their respective 'mother ships'.

PMT:

PMT stands not for what you may think but, in this context, for Photomultiplier Tubes.

PMTs are found in drum scanners and tend to provide the ultimate in image quality in the world of scanning.

PPI:

Pixels Per Inch, see Resolution below.

Posterization:

The uneven transition of tones from one tone to the next.

Often (though not entirely accurately) referred to as banding, this phenomenon can often appear in skies where smooth gradations of color and tone are crucial but sometimes difficult to achieve.

Profiling:

A process of measuring multiple specified color patches in order to accurately describe the color capabilities of a digital device (such as a scanner, camera, monitor or printer).

Not to be confused with calibration (see definition above), this measuring process usually results in the creation of an ICC Profile (also see definition above).

PSD:

Adobe Photoshop's native file format: Photoshop Document

This file format is ideally suited to saving and storing files that contain layers, paths and alpha channels as well as other features specific to Photoshop.

RAM:

Random Access Memory.

A form of memory used in a computer to store data on a rapid temporary basis to speed up the computer's immediate performance.

As they say, "You can never have too much RAM!"

This is actually a slightly silly thing to say as there is always an upper limit to how much can be fitted in a computer!

RAM is different to storage in that no data is permanently written. The user isn't able to choose how or where data gets written to RAM; everything is controlled and determined by software and hardware configurations.

At the time of writing, 2-4GB is par for the course and a state-of-the-art Apple Mac Pro can take up to 32GB.

So, it would perhaps seem more sensible to say, "You can never have too much RAM, as long as it's not more than 32GB!"

RAW:

RAW is a digital image file format produced by scanners and cameras.

It does what it says on the tin and captures raw, untouched data.

All scanners and cameras capture raw data at the start of the process but only some equipment actually lets you save it and work with it afterwards.

If you have the facility, always shoot RAW, as described in my RAW File Format article.

Resampling:

Making a digital file larger or smaller by increasing or reducing the number of pixels.

Downsampling reduces the quantity of pixels and upsampling increases the quantity of pixels.

Resizing:

Making a digital file larger or smaller by maintaining the same number of pixels.

Therefore, if keeping the quantity of pixels the same (rather than adding pixels or taking them away), the height, width and resolution will always be connected and alter their relationship to each other accordingly.

For example, if a file is downsized by reducing the height and width, the resolution will increase as the same number of pixels must fit into a shorter distance.

Conversely, if a file is upsized by increasing the height and width, the resolution will decrease as the same number of pixels must now spread over a greater distance.

Resolution:

1. Digital Image Files:

   A digital image file is comprised of a quantity of pixels.

   The frequency at which those pixels occur within a specified distance defines the resolution of an image.

   Common units of resolution are pixels per inch and pixels per centimetre; not to be confused, as is commonly the case, with dots per inch for describing output devices (dpi).

   300ppi is considered to be a standard print resolution and 72ppi is screen resolution.

   Beware, however, as resolution means little without also knowing the total quantity of pixels!

   A file may be 300ppi but only 300x300 pixels in height and width (one inch by one inch). This is not very much information despite the high resolution.

2. Printers:

   Printer resolution is different from file resolution and the two are not connected (they are not interdependent)!

   Only use the term dots per inch or dpi to describe the resolution of an output device that prints using dots, such as an inkjet printer!

RGB:

Red, Green and Blue, the three colors that form the foundation of all digital capture processes.

In digital photography Red, Green and Blue are the primaries of transmitted light and, therefore, it is not possible in the digital arena 'to shoot in black and white' or 'to scan in CMYK' as all data starts as RAW or RGB at some point, from which it can then be converted to some other form...

Saturation:

The purity and, therefore, apparent intensity of a color or tone.

The higher the saturation, the purer and stronger the appearance of the color or tone.

A highly saturated color is one comprised from a very narrow wavelength range.

Combining or contaminating the color with other wavelengths from the light spectrum makes it less saturated.

Scratch Disk:

A disk assigned to an application to offer it even more temporary memory and, therefore, to increase performance.

Ideally, the disk should be a fast hard drive dedicated to the task and not used for any other purpose.

Adobe Photoshop, for example, allows the user to assign up to four scratch disks via the application's Preferences and is a very simple way to enormously increase performance.

Sharpening:

Most digital capture processes rely on slight softening to enable smooth gradations and the faithful reproduction of colors and tones in an image.

Sharpening counteracts this by applying increased local contrast, usually just to edges.

A variety of software tools allow the user to apply judicious amounts of sharpening throughout the digital photography workflow in order to compensate for initial softening effect.

Sharpening is also appropriate when it comes to printing so as to make an image 'pop'.

Be careful though, as there is nothing so unsightly in digital imaging as over-sharpening!

SD Card:

Secure Digital is a type of solid-state flash memory card for use in certain digital cameras to store the digital photographs created by the camera.

Shutter Priority:

A shooting mode seen on many cameras with automatic metering capabilities (most cameras in the modern era!). It usually appears as TV in a menu or on a control knob.

Shutter Priority allows the photographer to select the desired shutter speed, the camera will then automatically select the appropriate corresponding aperture to make the correct exposure.

Spot Metering:

A method of making an accurate light meter reading from a tiny area of a camera's field of view.

The area from which the reading is taken is usually 1% or less.

TIFF:

The Tagged Image File Format is perhaps one of the most robust file formats around.

I use TIFF as my preferred choice to supply finished files to clients.

Although they do now support layers and other Photoshop features, I would strongly recommend saving files containing those features as PSDs (see definition above).

Use TIFFs for your RGB, Grayscale or CMYK master files with all layers flattened and alpha channels removed.

White Balance:

A system used to describe the color temperature of the light source used in the making of a color photograph.

The normal aim is to adjust the white balance of an image to 'neutralise' it; to make blacks, greys and whites appear neutral.

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I hope you have found this glossary of digital photography terminology helpful.

Several terms have been added in response to requests from visitors like you.

In fact, whole new articles have been written as a result!

If you feel there is something to add, a detail is missing or needs clarifying, don't forget to return to the top of this page and let me know!

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