MP4 is a video file format used by many digital cameras. It’s simple to work with because it produces a single file containing both the video and audio and it’s simple to drag from one device to another. It’s often provided as a similar alternative to AVCHD on Sony and Panasonic cameras.
Definition
Mount adapter
A lens mount adaptor which lets you mount a lens designed for one camera or brand on a different make or type of camera. For example, you can get adaptors for fitting DSLR lenses on some mirrorless cameras. Mount adaptors (lens adaptors) are used widely in videography.
Montage
Two or more images combined, usually using layers in a program like Photoshop or Affinity Photo.
Monopod
One-legged camera support that lacks the stability of a tripod (obviously) but offers invaluable support when using long, heavy telephoto lenses, and very popular amongst sports photographers for that reason.
Monitor calibration
Monitors rarely display colours with complete accuracy, so some professionals use calibration kits that use a sensor to read the monitor’s colours and then apply a software profile to correct the display.
Moiré
A fine interference pattern sometimes visible when you photograph fine patterns. It happens when these clash with the rectangular grid of pixels on the camera sensor. Actually, you almost never see it – most cameras have anti-aliasing/low pass filters to prevent, and it doesn’t seem to be an issue for those that don’t.
Modifier (lighting)
A lighting modifier is designed to change the character of the light from a flashgun, or some other source of artificial lighting. Mostly they soften or diffuse the light, or change its direction.
The most common type of lighting modifiers are the softboxes, brollies, honeycomb grids and other accessories attached to studio lighting systems. However, it’s also possible to get lighting modifiers that attach to regular camera-mounted flashguns, providing a reflective surface for bounced flash or a mini-softbox for smoother and more even lighting.
Modelling lamp
A continuous light built into many professional flashguns so that you can see the effect of the light ahead of taking the picture. Without a modelling lamp, you won’t really be able to gauge the effect of the lighting without taking a shot and looking at the result.
Traditionally, modelling lamps were much lower-powered than the flash unit itself and not designed to provide illumination for taking pictures on their own. However, the increased use of video and its need for continuous lighting has mean that flash makers are now incorporating LED lamps which can be used for this kind of continuous lighting application.
Mode dial
Just about all digital cameras have these or an equivalent and you use it to set the exposure mode, such as full auto, program auto exposure, scene modes, movie mode and so on. More advanced cameras add PASM modes – Program AE, Aperture-priority, Shutter-priority and Manual.
Mirror up mode
An option on more advanced DSLRs that flips the mirror up in advance of the exposure in order to give any vibrations from the mirror mechanism time to die down. It’s popular with fans of macro photography and some landscape photographers.
Miniature effect
Special effect provided in some cameras and image-editing programs which makes real-world scenes look like miniature models. It does this by blurring the top and bottom of the image to simulate the shallow depth of field of a close-up shot.
Midtones
Very broadly, the middle brightness tones in a photo. Imagine the full range of tones in an image split into four equal parts – the darkest quarter makes up the ‘shadows’, the lightest quarter makes up the ‘highlights’ and in between are the ‘midtones’.
Microphone
Any camera which shoots video will have a microphone built in, often stereo mics. For serious video work, though, an external microphone is needed. Some types plug into the camera’s hotshoe, others are used on the end of a boom or clipped to a presenter’s clothing (lapel mics).
Microlens (sensor)
In order to maximise their light gathering power, each photosite on the camera sensor is covered by a tiny domed ‘microlens’ to capture and funnel in the light more effectively. Improvements to the microlens array can improve the sensor’s performance.
Micro Four Thirds (MFT)
This is a sensor and lens format used by Olympus and Panasonic for their mirrorless camera ranges. The MFT sensor measures 17.3 x 13.0mm, so it’s smaller than the APS-C sensors used in rival mirrorless cameras. This does have a modest effect on overall image quality, but the payback is the both MFT cameras and lenses are substantially smaller and lighter than rival APS-C models. The MFT format also has a slightly squarer 4:3 (four-thirds) aspect ratio, which some photographers might prefer.
Metadata
Any information embedded in a digital photo. It can include time, date and shooting information (EXIF data) embedded by the camera, keyword, caption and copyright (IPTC data) added by image cataloguing programs and, sometimes, image processing data added by non-destructive image-editing programs. See also: The ticking time-bomb of non-destructive editing.
Merge (HDR)
HDR (high dynamic range) images are usually created by blending a series of different exposures of the same scene to capture a wider brightness range than the camera could capture with a single exposure. These are then blended together by HDR software using a ‘merge’ process.
Memory card speed
Memory card makers quote the card’s maximum read/write speed in MB/sec, but it’s also important to know the minimum sustained speed for video recording. This is quoted using Class ratings (SD cards). Typically, you need Class 10 for 4K video as a minimum.
Memory card capacity
This is measured in gigabytes (GB), and the larger the memory capacity the more photos and video clips you can store. It’s hard to give precise advice since cameras and user needs vary so much, but 16GB is a good starting point if you shoot RAW files as well as JPEGs, and consider 64GB-256GB if you want to shoot video, especially 4K.
Megapixels (MP)
The number of pixels captured by the camera’s sensor. Smartphones typically have around 8 megapixels and upwards, while regular digital cameras typically have 16 megapixels or more. Megapixels used to be a good guide to image quality but now sensor size is more important.
Medium format
Professional cameras that use sensors larger than full frame. These fill the space previously occupied by 120 roll film cameras, though they are massively more expensive. ‘Medium format’ sounds like there should be a larger size still, but it harks back to the days of film when you could get large format 5×4” or 10×8” sheet film cameras.
Mechanical shutter
The traditional form of camera shutter, a physical device which blocks light from the sensor until the moment you press the shutter release, then opens to expose the sensor for the required amount of time before it closes again. Mechanical shutters are either focal plane types, just in front of the sensor, or in-lens ‘leaf’ types.
Electronic shutters offer shorter shutter speeds on paper, but with current technology they’re less effective at capturing fast-moving objects.
Maximum aperture
The maximum light-gathering power of a lens and a major selling point.It lets you use faster shutter speeds or lower ISO settings in poor light.This lens has a maximum aperture of 1:2.8. This is the same as f/2.8 – different makers use slightly different terminology.
Mask
Related to selections, but a more permanent way of masking out adjustments made to an image. For example, you might make an initial selection in an image-editor and then convert it into a layer mask which can be saved with the file and re-edited later if necessary.
Manual focus
Useful when you want to make the most of depth of field – with often means focusing between two objects rather than on one or the other. It’s also handy for ‘zone focusing’ in shoot-from-the-hip style street photography, where you want an instant shutter response.
Manual exposure
Where you set both the shutter speed and the lens aperture used by the camera. The camera’s exposure meter may recommend the settings, but you’re free to use or ignore this information. Manual exposure gives you total control but requires some experience.
Managed files
Image cataloguing programs store a database of images and their locations on your computer. Most will leave your image files where they are without moving them (‘referenced’ files) while others may offer to store your files within the image database (Aperture) as ‘managed’ files.
Macro lens
Strictly speaking, macro photography where a real-life object is captured at the same size on the sensor. So a bee 10mm long would form an image 10mm long on the sensor. True macro photography needs dedicated ‘macro’ lenses.
Macro mode
Many cameras and some telephoto lenses offer a ‘macro’ button or mode. This is rarely the same as true macro photography at 1:1 magnification. Instead, ‘macro’ is simply used as another word for close-up. This is the macro button on a Fuji X30 compact camera.
Luminar (Skylum)
Comparatively new image-editing software that offers instant effects presets made with a range of different filters and tools which you can combine and adjust manually. It offers easily-customised ‘workspaces’ which contain only the tools you need and which makes the interface as straightforward as possible.
Luminance (contrast) noise
The chief component in image noise and the one that’s most difficult to remove because software can’t easily distinguish between random image noise and real image detail. The result is that the more noise reduction you apply, the more you tend to lose fine image detail, resulting in images with obvious and objectionable ‘smoothing’.
LUT (lookup table)
LUT stands for ‘lookup table’. Essentially, it takes the colours in an image and remaps them on to new ones. It really is a table consisting of a large grid of colour swatches and how they should be adjusted in the converted images. Its closest equivalent is the device profiles used in colour management systems, which work on a similar principle, but LUTs are usually designed for creative effects rather than colour correction.
Low pass filter
A filter directly in front of most camera sensors to prevent interference (moiré) effects between any fine patterns and textures you photograph and the rectangular grid of photosites on the sensor. These filters actually blur fine detail slightly, and some makers no longer use them.
Low key
A photo where most of the tones are dark, such as a black cat in a coal cellar. You can also give photos a low key look with slight underexposure. It gives photos a dramatic, moody look, though the subject matter has to be right for this to work properly.
Loupe
In traditional film photography, this is a small magnifying eyepiece for examining the detail in a negative, slide or print. In digital imaging it’s a magnifying view for use on-screen. Aperture and Capture One use a digital representation of a loupe, while Lightroom has a Loupe view where you can zoom in and out.
Long exposure
Long exposures turn moving subjects like water and clouds into an atmospheric blur. The exposure time often needs to be several seconds or longer, so a tripod is essential. In bright light you’ll need a neutral density (ND) filter to get these long exposures.
Lomography
Company which champions old, analog cameras, outdated or cross-processed film and relaunched classic lens designs. Lomography products are known for their expense, sometimes makeshift construction and general unpredictability, but also revered by their fans for these very reasons (well, probably not the expense), because they introduce the kind of randomness, unexpectedness and engagement lost in the transition to modern digital imaging.
Local contrast
A relatively new type of image adjustment that splits a photo up into different areas, depending on its properties, and applies an optimum contrast adjustment to each. It’s used for a variety of ‘dehaze’ and similar tools. It’s also used as a kind of super-coarse sharpening which doesn’t make the edges of objects crisper in the normal way, but works over a much wider radius to give images more visual ‘punch’ from normal viewing distances.
Local adjustment
Adjustments made only to specific areas in a photo, not the whole picture. You pick out the areas you want to adjust with selections, masks or brush tools.
Live view
Where the camera displays what the sensor is capturing either on the rear LCD or in an electronic viewfinder. All compact cameras and mirrorless cameras are effectively in ‘live view’ all the time. It’s only out of the ordinary on a DSLR, which has to go into a special mirror-up ‘live view’ mode.
Lithium ion
Standard rechargeable battery type for digital cameras. Lithium ion batteries have good capacity, supply a constant output from fully charged until drained and have none of the ‘memory effects’ that affect other rechargeable battery types – you don’t have to wait until a lithium ion battery is flat before charging it again.
Liquify
A Photoshop mode for bending, pinching and distorting areas of an image to create a special effect or ‘improve’ the body shape of a subject. Other applications offer similar tools.
Lightroom Mobile
An app for iOS or Android devices which works alongside the desktop Lightroom app to display images you’ve synchronised via Creative Cloud. When sync a Collection in the desktop app, that Collection and its images will appear in Lightroom Mobile. You can view and even edit images in Lightroom Mobile and your changes will be synchronised with the desktop version.
Lightroom (Adobe)
All-in-one photo cataloguing, organising and editing tool that also synchronised with a mobile app so that you can browse and share your images while you’re on the move. It uses the same RAW conversion engine and tools as Adobe Camera Raw, which comes with Photoshop.
Light meter
A device for measuring light levels. Digital cameras come with their own sophisticated internal light meters, but it is possible to get external light meters where the settings have to be transferred to the camera manually. This is slower, but has advantages in some circumstances.
Light leak
Old and cheap film cameras have poor seals and badly-fitting backs that may let light through on to the film inside. This produces pale streaks across the image or at the edges and has become associated with an ‘old camera’ look. Some programs now replicate light leaks digitally in a variety of colours, patterns and orientations.
Levels
A basic image adjustment found in most image-editing applications. You can use Levels to inspect the image histogram and move the black point and white point sliders so that there’s a full range of tones from solid black to brilliant white.
Lens profile
Almost all lenses suffer from aberrations, including distortion, chromatic aberration and vignetting. These are difficult to eliminate optically in the lens design, so software publishers are increasingly offering lens correction profiles to do this digitally. The software can identify the lens used from the image’s EXIF data and then find and apply the correct profile automatically.
Lens modulation optimiser (LMO)
A processing algorithm used by Fuji in some of its cameras to counteract the softening effects of diffraction at small lens apertures, and image softness at the edge of the frame. It seems likely the LMO is simply applying some intelligent sharpening.
Lens hood
Lens hoods can reduce lens flare and improve contrast when there’s a bright light source just outside the edge of the frame, but they won’t help if the sun, for example, is in the frame. Lens hoods are usually ‘petal’ types that allow for the fact the image frame is rectangular.
Lens corrections
Lenses aren’t perfect – they all have optical aberrations of one sort or another. Now, though, many software applications have lens correction to correct these digitally, either with manual controls or automatic lens correction profiles.
Lens adapter
In principle, you can’t mix and match different types and brands of lenses with different camera bodies. Each camera maker uses its own bespoke lens mount and different mechanical and electronic connections between the camera body and lens. However, it’s often possible to make lenses fit different brands and types of bodies with lens adaptors. These are usually from third-party makers and designed for users who don’t mind a few compromises in camera functions. For example, you may lose autofocus functions and have to use manual focus only, and it’s likely that you’ll have to use manual exposure and lens aperture control rather than the camera’s full range of exposure controls.
Lens
The lens is a fundamental part of any camera. It’s what creates the image on the camera sensor (or film). Some cameras have a fixed, non-removable lens while others offer interchangeable lenses. Your choice of lens has a major impact on the appearance of your pictures, including the lens’s focal length (angle of view) and its aperture setting (which you may or may not be able to adjust). At a simple level the lens is just the thing on the front of the camera, but on a more advanced level lenses open up a whole world of photographic choices, buying decisions and technical comparisons.
LED lighting
New type of ‘continuous lighting’ that uses relatively little power but still provides enough light for video, still lives or portrait shots. Small LED panels can clip to a camera’s hotshoe, larger ones have their own stands and control panels.
Layers
Best thought of as a series of transparent overlays you can place over an image to add other images, text, effects or adjustments. You can also use masks to hide or show different parts of each layer and control the areas they affect.
Lavalier (lav) mic
This is a small microphone designed to attach to a speaker’s clothing for interviews or presentations, for example. They’re usually small and unobtrusive, they’re hands-free and they help exclude other background noises. They may also be called lapel mics. Some are connected to the camera or sound recorder by wire, others work wirelessly.
Lasso tool
A simple selection tool where you drag an outline around the object or area you want to select. The selection is ‘closed’ and ready for use when you finish the loop back at the point where you started. The Lasso tool is not very accurate but when used in conjunction with other selection tools and editing processes it can nevertheless be very effective.
Kit lens
A relatively inexpensive general purpose lens sold with a camera body as a kit. Buying both at the same time is much cheaper than buying them individually. Most DSLRs and mirrorless cameras are also sold ‘body only’ for those who already have lenses.
Keystoning
Where the tops of tall buildings appear to converge. This happens when you’re so close you have to tilt the camera upwards to get everything in. You can correct it by choosing a more distant viewpoint and keeping the camera level, or by using keystone correction tools in software.
RAW vs JPEG
Most digital photos are shot as JPEG images. This is a universal image file format that uses sophisticated compression to keep the files small and manageable. JPEGs are created by processing the RAW data captured by the camera. Some cameras let you save these RAW files instead. The files are larger and you need to process them later on a computer, but they offer the potential for better quality.
JPEG
This is a standardised, universal file format for digital photos that can be displayed by practically any device without any kind of conversion. It uses powerful compression to reduce the file size of digital photos so that you can get more on to a memory card or a hard disk, and they’re quicker to transfer. There can be some loss of quality (often invisible to the naked eye), so for ultimate quality many photographers shoot photos in their camera’s RAW format instead. It’s only more advanced cameras that offer this RAW option, and it produces much larger files which you will need to process yourself later on.
ISO expansion
This setting increases the camera sensor’s sensitivity to light. Each ISO step doubles the sensitivity, so it’s easy to use ISO as another exposure control alongside shutter speed and lens aperture. The more you increase the ISO, though, the more the image quality degrades.
Intervalometer
A camera setting or remote controller which fires the camera’s shutter at set intervals, stopping when it’s taken a specified number of images. The pictures can then be used to analyse movement or change over time or, more likely, combined to make a time lapse movie.
Interval timer
Sometimes called an ‘intervalometer’, this is a feature on more advanced cameras that takes picture at fixed intervals automatically. It’s most often used for time lapse photography. You set the interval between pictures and the number of shots you want the camera to take.
Interpolation
Using mathematical analysis to fill in the gaps in data. The photosites on sensors only capture red, green or blue light, so interpolation is used to examine surrounding pixels and calculate full colour values from those. When you increase the size (in pixels) of a photo, the software interpolates new pixels from the existing ones.
Inpainting (Serif)
An automatic object removal tool in Serif Affinity Photo. You brush over the object or blemish that you want to remove and the Inpainting Brush automatically fills in the area with pixels and patterns from surrounding regions. It’s quick and often very effective and comparable to Adobe’s ‘content aware’ retouching tools.
Infra red
A branch of photography that uses parts of the light spectrum not normally visible to the naked eye but which can still be captured on film or digitally using black and white or colour film made sensitive to infra red or a digital camera modified to remove the infra red filter that normally covers the sensor.
Import
With some programs you can’t just open an image straight away, you have to import it into the software’s catalog first. This is how database-driven cataloguing programs like Lightroom, Capture One and Aperture work.
Image editor
Any program which can edit, enhance or manipulate digital images is technically an image editor, though usually this term is reserved for more advanced, technical programs like Photoshop rather than simpler everyday photo management tools like Apple Photos or Google Photos.
Image circle
All lenses produce a circular image on the camera sensor or film, and this ‘image circle’ must be at least large enough to cover the full film/sensor area. Different lenses designed for different sensor sizes and formats have different-sized image circles. Lenses designed for APS-C format cameras, for example, have a smaller image circle than lenses for full frame cameras. Some specialised perspective control or tilt-shift lenses have larger image circles to allow for lens movements relative to the camera.
ILC (interchangeable lens camera)
Any camera where you can change lenses. Once, this was just DSLRs, but now mirrorless cameras are included in this category and, for the sake of argument, Leica’s ‘rangefinder’ cameras should be included too. ILC is not a widely used term but it is the most correct description.
iCloud
Apple’s cloud-based storage service, integrated into its desktop and iOS (iPhone and iPad) operating systems. You can use it to make your photos available on all your devices via iCloud Photos and the Photos app, though as with other cloud services, once you’ve used up your initial free allocation, further storage has to be paid for on a subscription basis.
IBIS (in body image stabilisation)
Short for ‘in-body image stabilisation’ and a term used by Fujifilm for its X-H1 pro mirrorless camera. In-body image stabilisers shift the camera sensor to counteract any camera movement during the exposure. It’s the first time Fujifilm has used in-body stabilisation, but it’s already used by Pentax, Panasonic, Sony and Olympus.
Hybrid autofocus
Autofocus system that combines contrast autofocus and phase detection autofocus. It works using special phase-detection sensors built into the sensor. Contrast AF is typically slow but accurate, while phase detection AF is typically fast if potentially less accurate.
Hue/saturation
A way of adjusting the colours in an image – the Hue adjustment shifts the colour along a continuous spectrum, while the Saturation adjustment changes its intensity. For example, you can shift the hue of leaves away from yellow towards blue and increase their saturation to make the leaves look ‘fresher’.
Hotshoe
Accessory shoe on the top of more advanced cameras that’s designed for sliding in an external flashgun, though these days it may also be used for electronic viewfinders, wireless remote control units and more.
Honeycomb grid
A honeycomb grid is a lighting attachment designed to narrow the light from a flash or continuous lighting source into a tight beam. It gets its name from the hexagonal shape of the holes in the grid. Where other lighting attachments are designed to spread and soften the light, a honeycomb grid is design to focus it tightly on a single area. It’s a type of light modifier.
History
Many programs can store a ‘history’ of all the editing changes you’ve made since you opened an image. Using this you can check what you’ve done and even backtrack to an earlier image state if you realise you’ve made a mistake. Some programs can store the history as part of the saved image file, while non-destructive editors like Lightroom will store it indefinitely as part of the image’s adjustment metadata.
Histogram
A graphical display of the brightness values in the picture. The darkest tones are at the left and the brightest on the right, and the vertical bars show the number of pixels for each brightness value. Histograms are an invaluable exposure aid when taking pictures, and when editing them later.
Highlight recovery
When you shoot RAW files there is often a little extra highlight detail in the data than is initially visible, and a good RAW converter will be able to recover this detail to correct any ‘blown out’ areas. There’s no much margin for correction, however – typically you might be able to recover 1EV of additional highlight detail, but rarely more.
High speed sync
High-speed sync is a flash mode that counters limited flash synchronisation speeds of focal plane shutters by pulsing the flash several times, potentially impacting flash power. Elinchrom’s ‘High Sync’ reduces this power loss.
Highlights
The lightest tones in a picture. It’s a pretty vague definition, but most photographers take it to mean tones which are at or near a full, featureless white. Retaining or recovering highlight detail – in bright skies, for example – is a big priority for keen photographers.
High key
A photo where the tones are predominantly bright or white. It’s partly the subject that makes a photographer high key – a white cat on a white cushion, for example, and partly the exposure technique – slight overexposure will give a high key look.
Healing
A process or set of tools for removing an object from a picture or repairing a blemish simply by painting over it. It’s like cloning, except that you don’t have to define a nearby clone ‘source’ to use for the repair – the healing tool chooses and matches pixels automatically.
Headphone socket
All DSLRs or compact system cameras which shoot video will have an external microphone socket for better sound quality – but for pro videographers it’s just as important to have a headphone socket for monitoring sound levels while shooting. You only get this on more advanced models.
HDR Efex (Nik Collection)
Software plug-in for creating HDR (high dynamic range) effects from single images or bracketing sets of exposures. It’s part of the Google Nik Collection. You can apply preset HDR styles with a single click or adjust and make your own effects using extensive manual controls.
HDR (high dynamic range)
HDR stands for high dynamic range photography. It combines a series of frames taken at different exposures to capture a much wider dynamic (brightness) range than the camera could capture with a single exposure. These exposures are merged using HDR software.
HDMI
Standard digital interface for connecting video and display equipment. Cameras have HDMI ports for direct connection to TVs, for example, but more advanced models can also connect to external monitors for video recording, or external video recorders.
HD video
‘HD’ stands for ‘high definition’ to distinguish it from older, lower resolution video standards. HD actually comes in two formats: standard HD has a resolution of 1280 x 720 pixels, full HD is 1920 x 1080 pixels. Both use the same 16:9 aspect ratio.
Handheld photography
Any photography – obviously – where you’re holding the camera with your hands rather than using a tripod or some other form of camera support. It has special implications for night and low light photography where it’s important to use shutter speeds fast enough to prevent camera shake.
Guide number (GN)
A measure of the power of a flashgun, whether it’s a built in flash or an external flashgun. You take the guide number and divide it by the subject distance in metres to get the lens aperture you should use. Flash power is usually controlled automatically these days, though, so the guide number is just an indication of the maximum power.
Group (lens)
Camera lenses used complex configurations of different optical elements, often cemented or fixed together in ‘groups’. Lens groups may be designed to counteract common optical aberrations and you may have autofocus ‘groups’ and zoom groups. Lens elements and groups often move relative to each other in complex ways as the focus and zoom settings are changed.
Grip
Also known as battery grips, these are accessories that attach to the bottom of some DSLRs or mirrorless cameras to offer extended battery life and, usually, a duplicate set of controls to make the camera suitable for extended use in portrait (vertical) mode. In some cases, a battery grip may also increase the continuous shooting speed of the camera. For example, the battery grip of the Nikon D850 increases its continuous shooting speed from 7fps to 9fps.
Gray card
Used for accurate white balance calibration, usually under artificial lighting where the colour of the light sources is unknown or variable. You can use the camera’s manual white balance preset control to take reading from the grey card, or set the white balance using the card and the WB eyedropper tool in many image-editing programs.
Grain
Film grain is caused by the random clumping of silver halide grains (black and white) or dye clouds (colour film) – the individual grains or colour spots are too small to see. Film grain looks very different to digital noise – many photographers use film grain simulation filters and tools.
Graduated filter
Graduated filters are clear at the bottom but darkened at the top, with a smooth, graduated blend in between. You use them in landscape photography to tone down bright skies without affecting the land. You can also create graduated filters ‘digitally’ in image-editing software.
Grading
The video equivalent of the image-enhancement stills photographers carry out on their images. Videographers ‘grade’ video to match the colours and exposures between clips, to create a certain ‘look’ or to edit video shot in a ‘log’ mode for extra dynamic range.
Gradient mask
An image mask that transitions from clear to opaque gradually using a soft gradient. It could be used to darken a bright sky in a landscape shot, for example, without producing a hard edge where the adjustment takes effect.
Gradient Map
A type of adjustment layer that translates the different brightness levels in a photo on to points on a gradient. It’s an effect you wouldn’t necessarily use that often, though you can effectively convert a colour image to black and white using a black-white gradient map, for example.
GPS
GPS receivers use global positioning satellites to fix the camera’s location and embed this in the photo’s metadata. You can look this up later and many programs can show the location the photo was taken on a map. Only a few cameras have GPS built in, but it’s standard on smartphones.