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While looking at pages relating to photography and images on Commons, users often encounter terms that might be difficult to understand. This is particularly true if the user's knowledge of photography is very basic, or if they are not a native speaker of English. This page aims to explain several of these terms in basic English, with the help of images. If you meet a term that you do not understand, please add it at the bottom of this page at Suggestions for terms to add to the list. If you know what one of these terms mean, please explain it is as simple a language as you can.
- A definition allowing one to understand what is being talked about (a link to Wikipedia is welcome)
- An explanation of why/when this is important in photography, and possible how to get a good result on this aspect.
- Please try and write in basic English: most users are not Native English speakers, nor are they photographers.
|Creation on commons|
Abbreviations of Photography TermsEdit
- AF: Autofocus
- BW, B/W or B&W: Black and white
- CA: Chromatic aberration
- CCW: Counterclockwise
- compo: Composition
- CW: Clockwise
- DOF or DoF: Depth of Field
- DS: Dust spots
- FOV: Field of view
- HDR: High-dynamic-range
- NR: Noise reduction
- OE: Overexposed
- OOF: Out of focus
- PF: Purple fringing
- UE: Underexposed
- WB: White balance
List of Photography TermsEdit
The aspect ratio of an image describes the proportional relationship between its width and its height. It can more commonly also be called "image size" or "image format" even if those terms usually means something else. Some of the most common ratios used in photography are:
- 4:3 (most common in the Micro Four Thirds system and in many point-and-shoot cameras)
- 3:2 (most common among APS-C and full-frame sensor cameras)
- 16:9 (most common for computer screens and TVs)
See also: Format shape
A problem of inaccurate colour presentation in photos where not every shade can be shown because there are not enough bits to represent them. Instead of a smooth gradient (light to dark nuance of a color), you see abrupt changes between shades of the same colour.
Black and white, (BW, B/W or B&W) is... (to be written)
Areas in a photo that are so overexposed or so bright that no details can be seen are often described as "blown" or "blown out". The areas are usually just pure white, but "blown" areas can also appear in colored parts of a photo when at least one channel (red, green or blue) is overexposed. This leads to color shifts, for example from blue to cyan in a blown blue sky.
When an area is "blown", no structure or details can be retrieved in it by any editing program since the information simply isn't there.
See also: Focus
An image is "blurred" when it is not displayed sharp and clear. To avoid blur and get clear images, it is generally neccessary to set the focus distance precisely to the correct value, which can usually be done automatically via autofocus.
The term bokeh is used to describe the aesthetic appearance of areas in a photo that are out of focus sufficiently to make them not only slightly blurry but create a more abstract, heavily blurred look.
Bokeh is often considered to be plesant when it is not distracting from the parts of the image that are in focus, makes the out-of-focus elements as blurry and unrecognizable as possible, and is devoid of any structure within the bokeh dots. As such, lenses with a wide maximum aperture (when shot at or close to that aperture), rounded aperture blades, a long focal length and well-corrected spherical aberration tend to produce the smoothest and strongest bokeh, although many aspects of the lens design can have an impact on the appearance.
When an object, usually branches and leaves, is photographed against a very bright, overexposed sky, the strong light can obscure the edges of the branches leaving only the center visible. The branches are said to be "burned out" since they in fact look like they have been partially consumed by fire. If there is some information left in the photo, the branches can be "filled out" to normal thickness in post processing with the help of an editing program, but most of the time this damage is irreparable.
Digital SLR (Single Lens Reflex). This is like a film camera, but instead of a film, there is an electronic sensor. It has a viewfinder. When you look through the viewfinder, a prism and mirror lets you see directly through the lens. When you take a photograph, the mirror moves out of the way, letting light through to the sensor. You can buy extra lenses to fit onto a DSLR. They can be very expensive. These lenses let you take photographs in very poor light, and very difficult situations, such as taking photographs of fast cars or sports.
A mirrorless interchangeable-lens camera (MILC), sometimes simply called a mirrorless camera, has an electronic viewfinder that shows the image directly from the sensor. This has the benefit that the camera can show information about this image, such as a live histogram, overexposed areas, a preview of the current exposure or areas that are in focus directly in the viewfinder, before the image is taken. As the name suggests, MILCs offer the ability to change the lens, making them as flexible as DSLRs and usually slightly more compact and more suitable for recording video. The most notable drawbacks compared to DSLRs are a focusing system that is often not quite as fast as that of a modern DSLR, as well as a smaller range of available lenses for most cameras, as most MILC systems are still quite young.
A bridge camera is a camera with a focus on good ergonomics and the ability to control most of the settings of the camera easily with dedicated buttons and dials, just like on a DSLR. Unlike with mirrorless ILCs, the lens of these cameras cannot be changed. The viewfinder is electronic, i.e. a screen which shows the image from the sensor. Sensor size and image quality are usually in-between compact cameras and DSLR/mirrorless cameras, sometimes just as good as the latter, with slightly less flexibility due to the fixed lens.
A compact camera is a "simple" camera. It is fully automatic and does all of the settings for you. It is easy to use and to carry. These cameras sometimes have extra controls to meet more specific needs, such as poor lighting conditions, but otherwise they work best in good light.
Chromatic aberration (CA) is an effect resulting from dispersion of light in which the lens can not focus all colors to the same point of convergence (i.e. the same position in the picture). It happens because lenses "bend" different wavelengths of light to different degrees.
CA most visibly appears as colored fringes along boundaries that separate dark and bright parts of the image in areas that are away from the center of the sensor. The fringes often show up in pairs with one color on one side of an object and another on the other side. These colors can range from blue through cyan to green on one side and from orange through red to magenta on the other. Sometimes, only one of the colors is present.
Removing chromatic aberrationEdit
Most of the advanced post processing tools have automatic, semi-automatic or manual tools for removing CA. These should be used if available as they preserve more detail than most manual methods and are far quicker and easier to apply.
There are, however, also ways to get rid of the unwanted green, red, purple or cyan "shadows" in a photo by using the regular tools in any image editing program.
Getting rid of CA in places that are almost black/grey/white is rather easy. Most programs have a tool to desaturate or remove color connected to a brush-tool of some kind. Set that to a size that just covers the CA you want to remove and move it over that place. The green or purple will turn grey instead and become as one with the rest of the picture. For places that are next to something with color, you select a tool with a brush for replacing color. You choose the color of the background close to the CA and move the replace-brush over the CA. For CA close to a part of heaven you can use the clone-tool and clone a bit of the sky right next to the CA over that CA to get the same shade of sky. To make it easier to work on the right area, first enlarge the picture to 100% to see where the CAs are, and then work on it at 200%. This will make it easier to hit the right spot.
Chromatic noise (sometimes shortened to chroma noise) or color noise is an area in a photo that is supposed to show only one color can be made up of a many colors that are very different from the color it is should be. Chromatic noise is usually not visible until you look at the photo at full size (100%), apart from photos taken at high ISO values. For example, a grey area can show red, green and blue specks. Some chromatic noise is always present in a color photo because digital camera sensors have noise on a pixel level, where different pixels are responsible for different parts of the color spectrum.
While some luminance noise is not usually very distracting, even relatively low levels of chromatic noise are quite visible in an image. Thankfully, removing chromatic noise is also much less problematic than removing luminance noise because noise reduction in the chroma components of an image will not affect most fine detail and humans do not notice loss of chroma information as much as loss of luminance information.
See White balance
Composition or compo is ... (to be written)
Compression artifacts, jpeg artifacts or just artifacts is... (to be written)
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Dead pixels or hot pixels are small dots in bright colors that can appear in a photo due to some technical error or camera shortcoming. The dead pixels occur in the original photo and are not the result of post-processing. Dead pixels are more common in long exposure photos taken in weak light, than in daylight photos. The spots are usually only visible when the photo is viewed at 100%. Click on the example photo to see them better.
Depth of Field (DOF or DoF) is decided by the given lens opening (aperture) or f/stop. It is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in a photo. A small aperture (large f/number: f/16, f/22, etc.) will give "large DOF"; the image will be sharp/in focus from the foreground to infinity. A large aperture (small f/number: f/1.8, f/2.8, etc.) will give "shallow DOF". Depending on the type of lens used, DOF can be as shallow a a few millimeters, for example when using Macro lenses or extension tubes. Good photographers know how to make use of DOF and/or use selective DOF to make their images more interesting. Some types of special lenses, known as "Lens Baby" can generate a very specific type of selective DOF, reminiscent to the imperfections of turn of the XIX century lenses, where the image gets blurred and/or distorted towards the edges. With a "Lens Baby" however, this selective focus blur/distortion can be controlled.
In photography, diffraction usually refers to aperture diffraction, where very small apertures (large f-numbers, like f/22) cause an image to appear somewhat blurry or unsharp. This is because light passing through a very small opening spreads out and becomes less focused; see Airy disk for more information. If you need a wide Depth of Field, but diffraction is making your images blurry, you may wish to consider Focus stacking.
This term, in general, refers to the reduction of the sampling rate of a signal. In photography, it is used to describe the process of reducing the pixel resolution of a given image, usually relative to the native resolution of the camera sensor with which the image was taken. This is often done to reduce the file size, to increase the perceived sharpness or to reduce the perceived noise level of an image when viewed at a 100 % magnification.
In downsampling, some information in the image is irretrievably lost, which is why it is generally discouraged on Wikimedia Commons.
Dust spot (DS) is... (to be written)
Photos taken with a digital camera are likely to have embedded Exif data, with automatically recorded date and time the photo was taken, exposure settings, focal length, and so on. You can read more about the use of Exif on Commons at Commons:Exif.
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Used on both digital and film SLR's as well as Mid-Format cameras (6×6, 4.5×6, 6×9 cm.) to achieve close focus in close-up and macro photography. To achieve close focus on large format (4×5″, 8×10″) technical cameras, bellows are used.
Field of view (FOV) or angle of view. The extent of the scene that can be captured on the camera sensor or by the eye. Typically the horizontal angle of view in degrees is used, but the vertical and diagonal angle of view can also be relevant. For a given distance, the field of view can be measured as an area, in metres for example. The human eye has a field of view around 135° vertically and 180° horizontally, though binocular vision only extends to around 120° horizontally. Much of this is blurred, however, so the area we can see well is limited to about 55°. This corresponds to the diagonal field of view of a 43mm lens on a full frame camera (i.e., a 50mm "standard" lens). An ultra wide angle lens of 12mm has a horizontal field of view around 120° whereas a telephoto lens of 300mm would only see around 8°.
To focus means to adjust the lens so that one part of your photograph is sharp. This is usually done automatically; some people choose to do it manually, although it is possible only with a DSLR camera.
To focus onEdit
To focus on something means to choose a part of the photograph in which you are interested, and thus want to be sharp.
When a subject or element is in focus, it means that this element is within the depth of field range around the focal plane. As a result, the element will be sharp in the resulting photo.
Out of focusEdit
When a photograph is taken out of focus, it means the whole photograph is blurry.
The focal length of a lens is defined as the distance between the centre of the lens and the focused image. However photographic lenses do not consist of a single thin element, so the physics becomes more complicated. The longer the focal length, the narrower the field of view seen by the camera sensor. For a full frame camera, a focal length around 50mm is considered "standard". A "wide angle" lens has a much shorter focal length, and a "telephoto" lens typically has a much longer focal length. A lens with a fixed focal length is called a "prime" lens, and a lens that can vary its focal length is called a "zoom" lens.
Focus stacking involves taking several photos with a gradual change in the focal plane relative to the subject and later combining these photos using image editing software. The focal plane can be adjusted either by changing the focus of the lens or by moving the distance between the camera and the subject.
Effectively, this makes it possible to extend the depth of field at a given aperture size. A tripod is almost always necessary for focus stacking to guarantee that the position of the camera does not change between the shots. The software can then easily align the photos and pick the most detailed area from each of the shots, combining them into one single image.
Focus stacking is especially useful in macro photography, where even relatively small aperture settings produce shallow depth of field, and an even smaller aperture would reduce the sharpness of the resulting image due to diffraction. It is also commonly used in landscape photography, when combining elements on the ground close to the camera with a distant landscape.
Landscape, portrait, square, or panorama are terms used to describe the shape of a photo, regardless of what is really photographed. The formats have been named after the sort of photos that are usually taken in that format.
- A landscape format is a photo that is wider than it is high:
- A portrait format is higher than it is wide:
- A square format is exactly as high as it is wide:
- A panorama format is often very wide in relation to height:
A file format is a standard way that information is encoded for storage in a computer file. There are some common formats used for photographs or graphics.
- JPEG (or JPG) is a common format with irreversible compression. It is used for digital photography. The compression can cause visible artifacts (undesirable small distortions).
- PNG is a format with lossless data compression (the compression can be reversed) which also supports transparency. It is used for graphics or animations.
- TIFF is a universal format for graphic or photographic images. TIFF files can include lossy or lossless container formats and vector graphics.
- SVG is an XML-based format for vector images.
A digital camera sensor that has the physical size of a single frame on standard 135 film, which is 36 mm × 24 mm. This can typically be found on high-end DSLR and MILC cameras; most other cameras have smaller sensors. Despite the name, Full Frame is much smaller than both Medium and Large format.
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A type of chart that shows the brightness of an image by displaying the amount of pixels in each shade from complete black to complete white. The left side of the chart represents dark areas of an image (shadows), and the right side shows bright areas (highlights). The histogram is useful when taking digital photos and editing them, because it helps ensure a proper Exposure. If all or almost all of the pixels are somewhere close to the middle of the chart, you will usually have a good exposure. Photographers often discuss "clipping" the histogram; this means that significant parts of the image are so dark or so bright that they have no detail. If many pixels are leaning against or "clipping" the left side of the histogram, that means parts of the image are too dark, and you will not be able to brighten them later. If there are many pixels close to the right edge of the chart, parts of the image are too bright, and will appear simply as pure white. In this instance, your image may be described as "Blown out".
You can access a photo's histogram on your digital camera display and again in your editing software. It is most useful when you have trouble seeing your image, as in bright sunshine. If an image seems too dark or too bright, but the histogram is not "clipped", you will likely be able to save the photo.
It should be noted that, even when taking only RAW photos, histograms shown by the camera are based on the processed jpeg image in all currently available digital cameras. For this reason, a clipped histogram on the back screen of the camera does not necessarily mean that the information is actually lost and can not be recovered later. This problem can be mitigated to some extent by choosing a relatively flat color profile when shooting RAW.
See also: Lenses for SLR and DSLR cameras
The lens or set of lenses converts light toward the camera eyes. The quality of the lens allows for a clear image instead of a blurred one.
Technically, a macro image is an image taken with 1:1 or greater magnification at the sensor/film plane. This means that if the object were 30mm across, it would measure 30mm across on the film negative. Greater than 1:1 magnification is possible with true macro lenses, for example a 4:1 macro setting would enable a 5mm object to be 20mm across on the negative/sensor. The term has become misappropriated and used to refer to 'close up' photography in general, particularly by manufacturers of point and shoot cameras, whose lenses are rarely if ever come capable of anything close to true 1:1 macro magnification. Modern digital cameras have a macro mode. This is a mode which enables close focusing, allowing the maximum possible magnification from the camera/lens.
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Noise is random, mostly undesirable, variation of brightness or color information in photos, and is usually a result of electronic noise. It can be produced by the sensor and circuitry of a digital camera or it can originate in film grain in films for analogue cameras. Noise can also be added as an effect in post processing.
Noise reduction (NR) or denoising is... (to be written)
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Panning means panning or moving the camera in order to follow a moving subject. The result is a clear, sharp picture of the subject, with the surroundings blurred by movement.
For the effect to be noticeable, it is usually necessary to have a relatively slow shutter speed. This can be achieved by shooting with a small aperture, by using an ND filter, or by shooting in relatively low light. Panning will often become necessary with fast moving subjects in low light in order to keep the ISO low and achieve good image quality.
Keep in mind that, for extreme panning, the subject may change its orientation and size throughout the exposure. As a consequence, even a perfect pan may leave parts of the subject with motion blur. For example, panning with the cockpit of an aircraft can leave the wingtips and the tail slightly blurred.
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- For tips about How to make a panorama see Panorama on image guidelines
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Pixel peeping is a term describing the analysis of an image at a pixel level, i.e. at a magnification of 100% (one pixel in the file corresponds to one pixel on the screen) or higher. The term is often used in a derogatory manner, criticising a focus on small technical defects of an image, implying a lack of regard for other aspects such as the composition and subject of the photo. For more info, see this essay.
A lens with a fixed focal length (compared with "zoom" lens, which can vary its focal length). Advantages compared to a zoom are that it is cheaper to design a high quality prime lens, and easier to make one with a larger aperture. It will typically be smaller and lighter than a zoom covering the same focal length. The drawback to prime lenses is that one cannot vary the extent of the scene captured other that by moving closer towards, or further away from the subject, or by cropping the image afterwards.
Post processing or image editing is everything that is done with a photo after it has been taken. The alterations and improvements of the photo are done with editing programs. Some cameras have very simple editing programs installed in the camera, that allows you to adjust the photo, but most post processing is done on a computer with a more powerful program. Some of the free programs are described at Commons:Software.
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Purple fringing (PF) or fringing is the term for an out-of-focus purple or magenta "ghost" image in a photograph. The fringing is generally most visible along the edge of dark areas adjacent to bright areas such as daylight or various types of gas discharge lamps.
The effect is usually a result of axial chromatic aberration of the lens, as well as other ways in which lens design is not optimized for very short visible light wavelengths.
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Reproduction ratio of 1:1Edit
A 1:1 reproduction ratio means that the image formed on the film or sensor is identical in size to the original object.
Lenses that are capable of producing such a magnification are called macro lenses. They need to be designed to focus to subjects very close to the very front element of the lens (the exact distance depends on the focal length). In most lenses, the maximum reproduction ratio that can be achieved is between 1:3.5 and 1:9, making them unsuitable for true macro photography.
Image resolution is the detail an image holds. The term applies to raster digital images, film images, and other types of images. Higher resolution means more image detail. Resolution of an optical system describes how close objects in real life can be while still being discernable as being separate in the resulting photograph. Because of varying acceptable levels of blurryness, resolution is not so easy to measure definitevely.
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Sharpness describes how accentuated/contrasted the edges of objects are. If not sharp enough, lines and edges appear blurry but when viewed in reality they have clear boundaries. Oversharpening in software can cause halos/glowing margins around edges. The term is often misused when someone meant to describe resolution.
Stitching is the process of combining multiple photographs showing different parts of a scene, thereby creating one large, seamless image. This has two main benefits:
- It allows a photographer to take an image of a higher total resolution than with a single photograph, and
- it allows for a wider field of view than the widest one possible with the current lens. For example, if the widest focal length of the lens is 18 mm and you want to take an image at 14 mm focal length, the only way to achieve that with this lens is by taking four images at 18 mm, changing the orientation between those 4 photos to cover the entire desired range, and stitching those photographs together using software later.
A stitching error is a point in the image where the seam between two images is still noticeable in the final result. This is usually the result of
- differences in exposure
- a slight shift in the camera position between shots (more precisely a shift of the point of no parallax of the lens),
- a failure of the stitching software to correctly align the photographs because it could not recognize good overlapping features, or
- a failure of the stitching software to correct for lens distortion, vignetting or other aberrations.
To avoid the most common errors, you should shoot stitched images with a locked manual exposure whenever possible to achieve matching brightness between frames, and use a tripod to make sure the camera does not move between frames. Manual focus can also help guarantee that the focus does not shift between shots. Changes in the position of the point of no parallax are more critical the closer you are to the closes object in the photograph. Therefore, it is sometimes (especially for indoor scenes) necessary to use specialized panoramic rigs to move the camera around precisely the right point, which is usually somewhere around the front element of the lens.
Stitched images are sometimes also referred to as panoramas, though technically, that term only refers to the wide aspect ratio common among images that have been stitched together horizontally. Consequently, a panorama can also be achieved by cropping a regular wide angle image (see Panorama).
Making a stitched image - example
The photographer's own comment about making a stitched image:
"Having planned this for a while, I finally had an evening with suitable light and weather conditions. The light conditions changed very quickly so it wasn't easy to find the right settings to have a short exposure (to avoid that the first frames of the stitched mosaic were differently exposed compared to the last frames) and to get the water of the river Spree smooth (for this purpose I'd preferred a longer exposure even more but then the light situation would have change too much in-between the single exposures). For the same reason I used a 35mm lens in this case, instead of the 50mm: I wanted to have less frames to take."
"The dynamic range of the scene was very high so I had to use the HDR technique. To have a short exposure I decided not to take five exposures as usual, but only three exposures (-2 EV, 0 EV, +2 EV) for each frame. For the stitching itself I had to play around a little bit with different kinds of projections. In the end I chose a 'Vedutismo' projection because the rectilinear projection caused extreme stretching for such a wide field of view. Regarding the crop I decided to use a 16:9 ratio because 2:3 would have ended in too much empty space at the top and the bottom. Placing the buildings right in the middle of the picture follows the rule of thirds."
For more tips about making good stitched images see Panorama Howto (at the moment only in German).
Strip or slit photography. The best way to understand how strip photography works is to imagine that you are standing with your camera in a fixed position behind a door that is only open a very small crack. You rapidly take photos of what you can see through the crack from that point of view. At first nothing happens so your photos will all be a very thin vertical line that looks the same in each frame. Then something, a streetcar, passes by the crack and you get a small piece of the vehicle in each of your photos. When it has passed by the opening, the scene may go back to what it was before and once again all the photos you take of the crack will look the same.
After shooting this sequence, you take all the photos and crop away all the black around the crack in the doorway, leaving you with lots of photos of just the crack and you paste them side by side in chronological order. As you do this a photo of the streetcar as it passed the crack will start to appear. If you were taking photos at the same time-interval during the shooting session and the car moved at a constant speed, you'd end up with a photo like the one in this example.
Imagine if the car had slowed down, then you would have got more photos with it in the crack towards the end of the session and the back of it would have been sort of "drawn out". And if it had stopped in front of the crack all your photos until the end of the session would have had a bit of streetcar in them that looked the same until the end. This is done with a special camera that shoots only a slit that is two pixels wide and the photos are taken in an automatic fashion to make sure the time between shots is the same and the shots are merged into a photo with software, but the principle is the same as photographing through a crack in the doorway.
Refers to a photo taken indoors where a subject is set up and photographed under controlled conditions. A studio shot can be made under conditions as simple as photographing something on a kitchen work top with the overhead lamp as light source, or it can be done in a dedicated room with special backdrops, studio lights, screens, reflective surfaces and other professional equipment.
Strictly, a "telephoto" is a design of lens where it is physically shorter than its focal length, but the term is commonly used to refer to lenses with a long focal length and a narrow field of view.
Texture photography refers to photographing a surface, pattern, repetition or clutter rather than a scene or composition. The key components for such photos are colors, light and depth. The texture usually fills the whole image, giving the impression that the photo is just part of something that goes on forever outside the frame.
Tilt, rotation, rotated refers to cases where the vertical axis in an image is not aligned with the vertical in the scene that was photographed. This results in horizons not being level as well as buildings and trees leaning towards one side. Even in the absence of a visible horizon or perfectly vertical structures, a tilted image will usually look unbalanced.
In rare cases, tilt can be intentional and make an image more interesting. This is called a Dutch angle.
When describing the amount that an image is tilted, people usually give an amount of x degrees of tilt to the left (rotated cw, short for clockwise) or right (rotated ccw, short for counterclockwise). To correct the tilt, a rotation by that amount in the opposite direction must be applied.
A level horizon is only one way of determining if an image is tilted, and this method is often not practical due to the horizon not being visible in the image — either because it is not in frame or because it is hidden behind hills, structures or objects. In these cases, a good way of determining the tilt is to find structures that are perfectly vertical (often found on buildings) or reflections of features in water. Because water will almost always be horizontal due to the force of gravity, a line through a feature above the water and its reflection in water will usually be perfectly vertical.
The terms upsampling or upsizing refer to the process of increasing the resolution of an image though interpolation, i.e. stretching out the same image across more pixels. This can either be from the native resolution of the camera sensor or based on an image that was previously downsampled.
In almost all cases, upsampling increases the file size while adding no additional information. For this reason, images on Wikimedia Commons should, in general, not be upsampled. In many cases, some information will actually be lost when an image is upsampled (depending on the upsampling ratio and the interpolation method that is used).
An exception where information in the image can be increased in upsampling (compared to keeping the resolution the same) are steps in image processing where any geometric transformation is applied to an image. This could be applying perspective or distortion correction (ideally done based on a RAW file) or creating a stitched image. In these cases, upsampling can reduce the amount of information that is lost through the tranformation.
Vignetting is a reduction of an image's brightness or saturation at the periphery compared to the image center or in plainer words, it is a soft darker border along the sides of the photo. Vignetting can be a result of how the light enters the camera lens or it can be added in post processing as an effect. The vignette can be of any size, intensity and shape. It can be just darker corners in the photo or around the whole edge of the photo, leaving a square or round central area.
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A lens that can vary its focal length (compared with "prime" lens, with a fixed focal length). Zoom lenses are popular and convenient as they allow you to easily change the extent of the scene captured without having to move or change lenses. However, they are heavier and larger than prime lenses, and it is expensive to make them of high quality. The maximum aperture of a zoom lens is usually smaller than a similar prime lens, and this may vary depending on the focal length the lens is set to. A zoom lens that maintains the same bright maximum aperture throughout the focal length range is known as a constant (or fixed) aperture zoom, and this is considered a desirable property. The "kit lens" that is often sold with a DSLR often has a variable and small maximum aperture, as well as other optical compromises to achieve low cost.