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Alpha channel
Alpha channel carries information about the degree of opacity for each pixel and is one of the four channels (red,
green, blue, and alpha) that defines the total color of the object (sprite). It is also a temporary storage area
for masks. When a mask is saved to an alpha channel, that mask can be accessed and reused in the image as many
times as wanted. Alpha channel can be saved to a file or a previously saved channel loaded in the active image.
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Channel
Channel is a medium for transferring color information to the pixels of a display monitor. Also, channel is an
8-bit grayscale image that stores color or mask information for another image. There are two types of channels:
color and mask.
1. Color Channel
Color Channel is an 8-bit grayscale version of an image. Each channel represents one level of color in the image;
for example, RGB has three color channels, which carry the information of RED, GREEN and BLUE. CMYK
has four color channels, which carry the information of CYAN, MAGENTA, YELLOW and
BLACK. When all the channels are printed together, they produce the
entire range of colors in the image. So, images have one color channel for each component of the color model on
which they are based that contains the color information for that component.
2. Mask (alpha) Channel
Mask Channel stores masks that are created for the images and are saved with images in formats that support mask
information (e.g., .CPT, Corel Photo-Paint). So, the image editing program must support alpha channel.
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Color Depth
Color depth indicates the number of colors that a file can support. A 1-bit file supports two colors (usually black
and white), a 2-bit file supports four colors, a 4-bit file supports 16 colors, an 8-bit file supports 256 colors,
and a 24-bit file supports 16 million colors. A grayscale image is an 8-bit file, with 256 increments, ranging
from black to white. The higher the color depth supported by a file, the more space the file takes up on disk.
So, Color depth determines the range of colors and tones that are available in an image, and is usually measured
by the number of colors displayed, e.g., 256 colors, or 16 million colors. The color depth you select for your
image affects the file size, as well as the quality of the final image that is printed or displayed on a monitor.
Color depth is identified by a number of bits. For example, Corel TWAIN allows you to choose from the following
color depths:
32-bit: color depth is using 24 bits per pixel to represent a color image in a computer with an additional
eight bits for an alpha channel.
24-bit: 16 million colors,
8-bit: 256 colors,
8-bit greyscale: 256 grays, and
1-bit: black and white.
The number of bits a color uses dictates both the horsepower it requires from your system as well as the number
of colors or shades it is capable of producing. One bit can either be on or off, so 1-bit color is capable of producing
just two pixel depths:
0 (off) results in a white pixel, and 1 (on) results in a black pixel.
On the other end of the scale, 24-bit color has more than 16 million possible pixel depths (colors), and requires
a great deal more memory.
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Color mode
A system that defines the number and kind of colors that make up a bitmap image. Black-and-White, Grayscale, RGB,
CMYK, and Paletted are examples of popular color modes.
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Color model
A method for representing color. Colors can be described using several different color models: HSV (hue, saturation,
and value); CMYK (cyan, magenta, yellow, and black); and RGB (red, green, and blue). Microsoft Image Composer uses
the RGBA (red, green, blue, and alpha) color model, which includes transparency information.
A simple color chart that defines the range of colors displayed in a color mode. RGB (red, green, blue), CMY (cyan,
magenta, yellow), CMYK (cyan, magenta, yellow, black), HSB (Hue, Saturation, Brightness), HLS (Hue, Lightness,
Saturation), and CIE L*a*b (Lab) are examples of popular color models.
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Dithering
A method of controlling how colors specified by a composition are approximated on a display system or in a file
format that does not have the specified color available. Custom palettes allow you to choose from four types of
dithering: solid (for no dithering), error diffusion, random, and pattern. You can control color in several ways.
You can:
·Use the True Color palette, to display true color on display systems that use a 24-bit graphics adapter
video card.
·Use one of the custom color palettes:
·Gray Ramp has 236 shades of gray ranging from pure black to pure white.
·Web (Dithered) has 216 colors and uses the Error Diffusion dithering option. Use this palette for photographs
or other types of images that you want to publish to the Web. If this palette does not include a color needed by
an image that you insert in your composition, it uses the nearest matching color from this palette.
·Web (Solid) has 216 colors and uses the Solid dithering option. Use this palette for line art or solid-colored
art that you want to publish to the Web. To avoid dithering, the Web (Solid) palette includes the minimum set of
colors that should always be available to all images, regardless of the operating system or the browser used to
display the image.
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Lossless
The maintenance of image quality of an image that has been compressed and decompressed. The process of compressing
and decompressing often degrades image quality. A lossless image is one in which the image quality of a decompressed
file appears nearly identical to the original. GIF format is lossless.
GIF file format
The GIF file format was developed as a cross-platform graphic standard, which means that it is supported by all
graphical Internet browsers. GIF supports up to 8-bit color (256 colors) and lets you create custom palettes for
your image. GIF offers several advanced graphic options, including transparent backgrounds, interlaced images,
and animation.
The GIF file format uses lossless compression, which means that when you convert an image to the GIF file format,
all of the file information is stored within the image so that the GIF file looks exactly like the original image.
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Lossy
A noticeable degradation to image quality as a result of file compression. Choosing high quality compression often
results in very little loss of perceptible information. The lower the quality of compression, the poorer the image
quality will be when the image is decompressed. JPEG format is lossy. Still, there is an exception, if you
have a graphic program that can alter the compression volume, you can either enhance or reduce the quality of tyour
images.
JPEG file format
The JPEG file format was developed as a compression scheme designed specifically for computer images. JPEG supports
up to 32-bit color (4.2 billion colors) and is, therefore, an excellent option for photographs, image maps, and
scanned color images.
JPEG files use lossy compression, which means that the image loses information while continuing to provide high-quality
images with a high level of compression. You can choose the image quality by a simple method that goes; the higher
the image quality is, the larger is the file size. Some Web browsers support progressive JPEG images. Progressive
images appear on screen gradually so that you can see portions of an image before it finishes loading (basically,
this is out of time and not so practical).
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Mask
Selection tools that isolate the area that you want to protect from change when you apply color, filters, or other
effects to an image. Masks act as protective layers or sheets that cover areas on an image. These areas are not
affected by editing changes that you apply to the image. The rest of the image is affected by the editing changes
that you apply and is outlined by a mask marquee.
When you select an area on your image using a mask tool, the area that you select is editable and the rest of the
image is protected by a mask. You can create regular and color-sensitive masks. Selection is a section of the image
that is not protected by the current mask and that is, therefore, available for editing. The selection is affected
by the use of painting and editing tools, special effects, and image commands. When you apply the mask overlay,
the selection is represented by the transparent areas of the overlay.
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Object
An object is an independent bitmap that is layered above the background image. Transformations applied to objects
do not affect the underlying image. Same as sprite.
You can create an object from scratch using the brush and shape tools. You can use the brush tools to create an
object from paint strokes or spray-on images, or to clone other objects. The shape tools let you create an object
from rectangles, ellipses, polygons, and lines.
You can create an object from the background to move, arrange, and change your image background as you can move,
arrange, and change any other object. You can also select parts of the background to create a new object. Embedded
object is the information from a file created in one application (the server application) that has been inserted
into a file in another application (the client application). For example, you can embed a graphic created in Corel
PHOTO-PAINT in CorelDRAW, Adobe PhotoShop in Adobe Illustrator.
You can apply transparency into the objects or any supported image effects, combine objects together, make multiple
duplicates of objects and position objects anywhere on the drawing area.
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Opacity
The opposite of transparency. If an area is 100% opaque, you cannot see through it.
Levels under 100% increase the ability to see through objects.
The quality and degree to which light cannot pass through pixels. A low opacity value makes pixels more transparent;
a high value makes pixels more opaque. You can specify opacity by using an opacity slider.
Many tool palettes and dialog boxes provide an opacity slider.
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Pixel
Abbreviation for picture element. Pixels are dots on a computer or television screen that combine to form an image.
Computer images are created as an array of pixels, each having a specific color.
A single unit of measurement on your screen that relates to the rectilinear grid used by display hardware to paint
images on your screen. These units, which often appear as tiny dots, compose the pictures displayed by your screen.
The color capability of each pixel is determined by the video card installed in the display system.
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Resolution
The amount of detail and information that an image file contains, as well as the level of detail that an input,
output or display device is capable of producing.
When you work with bitmaps, resolution affects the quality of your final output and the file size.
Image resolution
Refers to the spacing of pixels in the image and is measured in pixels per inch (ppi) or dots per inch (dpi).
Output resolution
Refers to the number of dots per inch (dpi) that an output device, such as an imagesetter or laser printer, produces.
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Sprite
A single image object, composed of pixels, whose area is defined by its bounding box. The sprite’s shape is determined
by its nontransparent pixels. To add a sprite to your composition, you can insert a file, create a shape, or add
text. Same as object.
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Transparent
The quality of a sprite’s pixels that defines the ability of light to pass through them. If a sprite is completely
transparent, light passes through it completely which makes the sprite invisible.
You can change the transparency of an entire object or you can change the transparency of part of an object. When
you change the transparency of an object, you change the grayscale value of its individual pixels. Grayscale values
range from black, which has a value of 0 (transparent), to white, which has a value of 255 (opaque).
Changing the transparency of an object evenly reveals the image elements that lie beneath the object. You can change
the transparency of an entire object by using the Opacity slider on the Property Bar for the Object Transparency
Brush tool, or you can change the transparency of parts of an object using the Object Transparency tools. The Object
Transparency Brush tool lets you change the transparency of an object by applying brush strokes. You can use the
Object Transparency tool to apply a transparency gradient to an object, or you can use the Transparent Color Selection
tool to make specific colors (or ranges of colors) transparent. To change the transparency of an object in relation
to underlying image elements, you can use the Blend controls in the Object Properties dialog box to specify which
pixels are visible.
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True Color
A term that refers to digital RGB color that is composed of
24-bits or 16.7 million colors.
The True Color palette mixes the reds, greens, and blues available on display systems that support 24-bit color
to produce 16.7 million colors. This is one of the highest fidelity color formats. If your display system supports
24-bit color, you can create compositions in true color. It is important to choose a palette that is supported
by the display systems that you plan to show your composition on. If you show a composition that was created with
the True Color palette on a display system, that does not support true color, the colors will dither and may appear
grainy or splotchy. In this case, consider using one of the custom color palettes that are provided or create your
own custom color palette containing up to 256 colors.
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