BGI Glossary: Image Editing

Image Editing

Acquire Module: Software that can expand the functions of the Adobe Photoshop program. Typically created by a scanner manufacturer, once installed it allows the user to perform scans while running Photoshop and to immediately have the scan available for image editing.
Anti Aliased: Anti aliasing an edge of an element or a mask is to give it a slightly soft edge that makes it appear smoother. It is similar to feathering by one or two pixels.
Bitmap: Another term for a line-art scan file or scanner setting. Refers to the pattern (map) of bits that are either black or white.
Black Limit: A color separation setting for the maximum allowable percentage of black ink in a CMYK image. This setting is made before an RGB image is converted to a CMYK image. The proper black limit setting is determined by the press and paper planned for the publication.
Black Point Adjustment: An adjustment made that will determine the amount of shadow detail in an image. It is considered proper to set the black point so that the darkest part of an image will only just have zero detail.
Channel: A part of an image in Adobe Photoshop. An RGB image has three channels, CMYK has four and line-art has one. The user can perform edits on individuals. Additional channels can be created to contain masks, type, patterns, or other images. These additional channels can be combined with the main image or used for special effects.
Clipping Path: A function of the PostScript language that allows a shape to mask part of an image. A clipping path shape acts much like a cookie cutter. Clipping paths are most frequently used in Adobe Photoshop to outline or silhouette an image.
Cloning Pixels: A function in image editing software that allows scratch removal or the removal of more significant portions of an image like telephone poles or a blemish on a models cheek. The function works by picking up pixels from another part of the image and painting them over the unwanted element. Pixel cloning can even be used cloning pixels from one image into another.
Color Cast: An image is said to have a color cast if its colors are not true. A color cast will usually be described by stating the particular color predominant in the image: "The grass appears to have a red color cast."
Color Correction: The act of correcting for and eliminating an unwanted color cast. Color correction is performed on an entire image (called global color correction) or on just one part (called local color correction.)
Color Separation: The act of converting an RGB color image into CMYK color image. The act of color separation is a technical function during which critical press specific settings such as GCR, black ink limit and total ink limit are applied to the image. If an image is already CMYK it would be described as being already color separated and would not need to be separated again.
Cropping: The act of discarding unwanted detail around the edge of a picture. Cropping in this way permanently discards the detail from the file and reduces file size.
DCS File Format: A color separated photo made up of 5 files. One each representing each of the process printing colors CMYK and one master file that is used for layout positioning.
Digital Densitometer: Image editing software has the ability to measure the values in pixels and read them out in RGB or CMYK. These values are accurate when compared with the actual values stored within the files and will remain unchanging regardless of which computer display the file is shown on.
EPS File Format: Encapsulated PostScript file. A file format commonly used for photographic and drawn graphics. An EPS file is created and later placed onto a page layout in a page assembly program.
EPS Rasterizer: A feature of Adobe Photoshop that allows a PostScript illustration saved in the EPS format to be converted into pixels for special effect editing.
GCR: Grey component replacement. A color separation setting used on color photographs where cyan, magenta and yellow inks are swapped out of an image (in a balance that would yield a grey value) and black ink is swapped in instead. The advantages are a reduction in overall ink usage, a more consistent press run, and some increase in image detail.
Grayscale: A term for a black & white photographic image or a scanner setting. Refers to the range of 256 grey tones that make up the image.
Hue: A measurement of color as can be related by pointing towards a certain color on the color wheel. Hue indicates the relative redness, blueness, greenness, yellowness, etc. of a color.
Image Assembly: An act where parts of two or more images are composited together to create a new hybrid image. A typical example of image assembly would be to position a picture of sunny blue sky into the background of a picture of the Seattle skyline.
Magic Wand Tool: A tool in Photoshop used to quickly select a part of a picture. If clicked on a the fender of a red car, the magic wand will select the entire fender and maybe the hood and door. A setting called "tolerance" allows the user to define the relative selectivity of the magic wand. A tight tolerance and the magic wand will only select the highlights of the car fender. A loose tolerance and the magic wand will select the green trees behind the car. The selections made by this tool always select areas that are connected and not divided.
Mask: A function within image editing software that allows the user to restrict their image edits to only a part of the image. A mask can have a hard or soft edge allowing the user to achieve a variety of obvious or subtle effects.
Noise: A term used to describe the occurrence of pixels within in an image that contain random colors. Also refers to a filter in Photoshop that can sometimes be used to give a smoother, more natural appearance to graduated screens. This filter is also used for special effects.
Opacity: A characteristic of painting and other tools within image editing software. By adjusting opacity to a percentage of less than 100%, the user can paint a color onto an image and allow some of the image beneath to show through. (Paint with transparent paint versus opaque paint.) This same characteristic is available while performing image assembly steps and allows one image to be transparently floated in front of or behind another.
Pixel: The smallest building block within a scanned line-art or photographic image. A pixel is the small square picture element that is filled with a color, or black or white. Pixels come in various sizes and their size is expressed in terms of resolution. Resolution is measured in pixels per inch (PPI.)
Printable Color: A term used to describe a color that falls within the gamut of a particular output device. A printable color will output as expected. Compared to a color that falls out of gamut which will print as an unexpectedly different shade. See also Gamut
RAM Needs: When deciding how much RAM you need in your computer, determine the average size of picture (expressed in MB) you will regularly handle. It is desirable to have 3 times that amount of RAM installed in your computer.
Re-sample an Image: A function available in image editing that allows the user to change the resolution of the image. Resampling an image is possible to any degree but there is a high quality penalty to pay if the image is resampled above 150% or below 50%. The quality loss will come in terms of decreased image sharpness. See also Re-sizing an Image
Re-sizing an Image: A function available in image editing software. Re-sizing an image is possible to any percent but there is a high quality penalty to pay if the image is scaled above 150% or below 50%. The quality loss will come in terms of decreased image sharpness.
Resolution of an Image: Expressed as PPI (pixels per inch.) The resolution of an image is a major factor that determines the attainable output quality. Proper resolution depends on the image type: Line-art should have a resolution of 600 PPI or above and photographs should have resolution twice the anticipated halftone screen frequency.
Rotate: A function found within image editing software that allows all or part of a pixel image to be rotated by any number of degrees. Rotation in 90° increments is fast and carries no quality penalty but this is not the case for other angles. This is why it is important to carefully orient artwork on a scanner so that rotation will not be necessary.
Selective Color Correction Adjustment: An adjustment available to allow specific colors within an image to be adjusted in regard to their color make-up: It is possible to take red out of green grass without affecting the red of the apples.
Silhouetted Image: A photographic image that has had its background erased so that the image can appear to float on the page layout. This is usually accomplished by selecting the edge pixels and coloring them white. It can alternately be accomplished by selecting the subject in the image and creating a "clipping path" from the selection. This clipping path will hide any image outside of this path and allow the subject in the image to float on a page layout.
TIFF File Format: Tagged Image File Format. One of the most common graphic file formats for line-art and photographic images. A TIFF file always consists of pixels; it can store information at any resolution the user requests and can include color or black & white data.
Tone Compression: A term used in scanning and image editing that refers to compressing the broad range of tones and colors in an image down to the narrower range available on a printing press.
Tone Curves: A term for an adjustment available in image editing software. Beginning as a 45° angle line running up to the right, this line is adjusted into a curve shape by the user to effect color or tone correction. The lower left end of the curve typically represents the dark portions of a picture and an upward bend will typically lighten the shadows. Similar capabilities exist by working with the middle or highlight parts of the curve. In this way it is possible to alter only certain tone ranges of an image without making un-wanted changes in other parts of the image.
Total Ink Coverage: Sometimes abbreviated as TIC. A term used in color separation to refer to the maximum allowable percentages of process inks (CMYK) in a photo on a press run. Expressed as a percentage number that is the total of the four colors; it is typically between 240% and 350% depending on the combination of press and paper types.
Transfer Adjustment: A command found in some image editing software to help calibrate the image files to correctly output on an imagesetter. This adjustment is typically left alone, and instead, the imagesetter itself is calibrated. See also Linearization.
UCR: Under Color Removal. A color separation setting used on color photographs where cyan, magenta and yellow inks are removed from dark, neutral areas and black ink is swapped in instead. The advantages are a reduction in overall ink usage. See also GCR.
Unsharp Masking: An important function that allows the user to add apparent clarity via electronic means. Unsharp masking is considered the most sophisticated sharpening method because it sharpens without the undesirable graininess that appears with other sharpening methods.
Virtual Memory: A computer term for a performance enhancing feature of some software. Virtual memory is a process where hard disk storage space is borrowed and caused to act as if it were additional RAM. The system will then be able to perform more complex functions just as if it had the additional RAM memory actually installed. See also RAM.
White Point Adjustment: An adjustment made that will determine the amount of highlight detail in an image. It is considered proper to set the white point so that the lightest part of an image will only just have zero detail.