Bitmap Graphics

9 Key excerpts on "Bitmap Graphics"

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  eBook - ePub

  Digital Images for the Information Professional

  • Melissa Terras, Melissa M. Terras(Authors)
  • 2016(Publication Date)
  • Routledge

    (Publisher)

  Chapter 3 Digital Image Fundamentals

  Pixel, noun: A mischievous, magical spirit associated with screen displays. The computer industry has frequently borrowed from mythology: witness the sprites in computer graphics, the demons in artificial intelligence, and the trolls in the marketing department (anonymous).1

  To understand issues regarding the capture, use, delivery, storage and preservation of digital images, it is necessary to understand the fundamental aspects of how digital images function. Given that the majority of digital images created by the home or professional user are bitmaps (see Chapters 5 and 6 ), this chapter details the fundamental characteristics of bitmap images and the underlying principles which drive bitmap representation: the individual pixels within the grid; the colour information stored about each pixel (bit depth); the spacing of individual pixels (resolution); changing image size (interpolation); and issues regarding file size and the compression of bitmap information. It also highlights various issues of relevance to the information professional working with digital image data.

  Pixels

  Bitmapped digital images work by fooling the eye. Any image can be divided into a uniform grid, with each element in the grid assigned a colour. Like an individual tile in a mosaic or the squares in a chessboard, each individual picture element is a discreet unit which has a place and a colour within the larger image. The human eye-brain system is keen to resolve this back into a continuous tone image.2

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  eBook - ePub

  The Image-Interface

  Graphical Supports for Visual Information

  • Everardo Reyes-Garcia(Author)
  • 2017(Publication Date)
  • Wiley-ISTE

    (Publisher)

  Data types allow performing, programming and iterating actions with them. For example, basic operations with numbers include addition, subtraction, division and multiplication, while operations with words are conjunction and disjunction of characters. However, data types can be combined and organized in order to support more complicated operations, as we will see in the following section.

  In the case of graphical information, there are two fundamental approaches to data types. From the standpoint of image processing and computer vision, the accent is placed on bitmap and raster graphics because many significant processes deal with capturing and analyzing images. A different view of data types is that of computer graphics whose focus is on vector graphics as a model to describe and synthetize 2D figures and 3D meshes that can be later rasterized or rendered as a bitmap image. We will now take a brief look at both perspectives.

  2.2.2.1. Data types and Bitmap Graphics

  The bitmap model describes an image as a series of finite numerical values, called picture elements or pixels, organized into a 2D matrix. In its most basic type, each value allocates one bit, thus it only has one possible brightness value, either white or black. The described image in this model is also known as monochrome image or 1-bit image.

  In order to produce gray scale images, the amount of different values per pixel needs to be increased. We refer to 8-bit images when each pixel has up to 255 different integer values. If we wonder why there are only 255 values, the explanation can be made by recalling Table 2.2 : the 4-bit column shows all the different values between 0000 and 1111 and their corresponding decimal notations. An 8-bit notation adds 4 bits to the left and counts from 00000000 to 11111111, where the highest value in decimal notation is 255.

  Nowadays, the most common data type used for describing color images is 24-bit color. Taking as primary colors the red, green and blue, every pixel contains one 8-bit layer for each of these colors, thus resulting in a 24-bit or “true color” image. As such, the color for a given pixel can be written in a list of three values. In programming languages such as Processing, the data type COLOR1

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  eBook - ePub

  Fundamental Data Compression

  • Ida Mengyi Pu(Author)
  • 2005(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  rendering. If the image is a line, only two end points are stored. When the model is rendered for display, a pattern of pixels has to be generated to display the line with the two end points.

  10.4 Bitmap and vector graphics

  The differences between bitmap images and vector graphics can be very obvious in terms of visual characteristics, but we are concerned more about the following issues:

  1. The requirements of the computer system: a bitmap image must record the value of every pixel, but vector description may take much less space for an image with simple structure, so may be more economical.

  2. The size of a bitmap image file depends on the display resolution. It is independent of the complexity of the image.

      In contrast, the size of vector graphics depends on the number of objects of which the image consists. It is independent of any resolution.

  3. The approach of the so-called painting programs produces bitmap images while that of drawing programs produces vector graphics.

  4. The behaviour of both bitmap images and vector graphics is different when resized or scaled.

  Most graphic applications today require a combination of bitmap and vector graphics. A transformation between vector graphics and bitmap images may be necessary. The following two processes are usually implemented for the transformation:

  Rasterising

  A raster is a predetermined pattern of scanning lines to provide substantially uniform coverage of a display area. Rasterising is the process of interpreting the vector description of graphics for a display area. A vector graphic loses all the vector properties during the process, e.g. the individual shapes can no longer be selected or moved because they become pixels.

  Vectorisation

  This is a more complicated process of transforming pixels to vectors. The difficulties arise from the need to identify the boundary of a pixel image using the available data of curves and lines and to colour them. The vector file tends to be much bigger than the pixels file before vectorisation.

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  eBook - PDF

  Compaq Visual Fortran

  A Guide to Creating Windows Applications

  • Norman Lawrence(Author)
  • 2002(Publication Date)
  • Digital Press

    (Publisher)

  223 10 Bitmap Graphics 10.1 Introduction This chapter describes the Windows API functions that deal with bitmaps and the manipulation of raster images. Pen plotters are vector devices, and the plotter pen draws a straight line between any two given sets of x and y coordinates. Curves are constructed by drawing a series of small straight lines. On the other hand, display screens and a great many printers are raster devices. The smallest unit that can be displayed by raster devices is known as a pixel, and images are constructed from multiple horizontal lines (often called scan lines) of pixels going from one vertical edge to the opposite verti-cal edge of the device. In a raster device, pixels are individually addressable, and straight lines are constructed by drawing a series of pixels (or dots) in a specified color between any two given sets of x , y coordinates. Curves are constructed by drawing a series of pixels in a specified color along the path of the curve. Because this can result in ragged looking lines, techniques such as antialiasing are often used to create smoother looking lines. Bitmaps are a way of storing data about how an image is to be displayed on a raster device. The simplest bitmap is of a monochrome image in which every pixel in the image is represented by a single bit with a value of 0 or 1. Bits that are set to 1 will usually be displayed in the current background color (e.g., white), and bits that are set to 0 will be displayed in the current foreground color (e.g., black). In color bitmaps, multiple bits represent each pixel and the number of bits per pixel governs the color displayed. Colors displayed on a screen are combinations of the primary colors red, green, and blue, and the total number of possible colors depends on the number of shades available for each of the primary colors.

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  No longer available |Learn more

  NEW PERSPECTIVES COMPUTER CONCEPTS 2016 ENHANCED

  • June Jamrich Parsons(Author)
  • 2016(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Selecting the best graphics file format to use depends on what you intend to do with the image. Figure 1-21 summarizes popular bitmap formats and their uses. Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 4 0 SECTION C, UNIT 1 BITMAP DATA REPRESENTATION The fact that bitmap images are formed by a grid of pixels controls not only how those images are stored, but also how they can be modified. Color and resolution are key elements in bitmap data representation.  How does each pixel get a color number? Today’s color display devices represent color using the RGB color model . The color displayed for a pixel is based on the intensity of red, green, and blue signals received by the screen’s color elements. Each red, green, and blue signal is assigned a value ranging from 0 to 255: 0 represents the absence of color, and 255 represents the highest intensity level for that color. A pixel appears white if the red, green, and blue signals are set to maximum intensity. If red, green, and blue signals are equal but at a lower intensity, the pixel displays a shade of gray. A pixel appears violet if it receives high red and blue signals and just a bit of green (Figure 1-22).  How are colors specified? Color values can be specified in decimal (base 10), hexadecimal (base 16), or binary (base 2). Even artists need to know their way around number systems! Decimal notation tends to be used within graphics software, and hexadecimal (hex) notation is common on the Web.

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  eBook - ePub

  Encyclopedia of Computer Science and Technology

  Volume 27 - Supplement 12: Artificial Intelligence and ADA to Systems Integration: Concepts: Methods, and Tools

  • Allen Kent, James G. Williams, Allen Kent, James G. Williams(Authors)
  • 2021(Publication Date)
  • CRC Press

    (Publisher)

  RASTER GRAPHICS

  INTRODUCTION

  The term raster graphics is most familiar to those who have studied the field of computer graphics. It refers to a subset of imaging technologies that has made a profound impact on our society. The term is hardly a household word, but one example of raster imaging is seen by many people daily—the television. Raster imaging currently is the most widely used form for manipulating images electronically, and in the broadest sense it refers to technology for image capture, manipulation, transmission, and display (i.e., photocopiers, video cameras, and facsimile machines). However, raster imaging is a far broader topic than raster graphics.

  Raster graphics is used to describe how computers are used to synthesize still images and animation sequences. However, it does not describe all of computer graphics. Raster graphics specifically refers to the generation and display of images represented by a dot matrix. Raster displays are composed of discrete spots of light, often referred to as pixels or pels (i.e., picture elements). If one looks very closely at a video display screen the individual pixels can be seen. Conversely, there are some computer graphic techniques that operate solely in the continuous domain (i.e., pen plotters that can mechanically draw continuous lines, as well as vector display screens). In raster display systems the electronics and the software must control each individual pixel as a separate step in the display process. The discrete nature of a raster display can be readily understood by imaging a view through a screen door. When standing close to a screen door, the eye can still see many variations within the small square holes. Despite the fact that there are only a finite number of light-sensing structures in the eye, images are perceived as continuous variations in intensity and color. A raster image is like a view through a screen door, except that only one color is used to fill a square—usually accounting for the contribution of all the colors within the square (see Fig. 1

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  eBook - PDF

  The Tao of Computing

  • Henry M. Walker(Author)
  • 2012(Publication Date)
  • Chapman and Hall/CRC

    (Publisher)

  For the 3·5 image stored at 300 dpi, this yields a requirement for 4,050,000 bytes of storage—about 4 megabytes. The pixel-by-pixel storage of all color information provides complete detail about every aspect of a picture, and this collection of information is called a bitmap (BMP) . Typically, a full file for a bitmap of one picture would include a header (with some type, format, and size information), general information (such as width, height, and resolution), and the image information—perhaps 3 bytes per pixel. On many computer systems, this material is labeled as a simple version of a “.bmp” file. Unfortunately, as our computation indicates, storage of all color information in such a file yields rather large files—even for relatively small pictures, taking up considerable space if they are stored or requiring significant time to download (particularly if one’s Internet connection is fairly slow). How Are Images Represented (and Does It Matter)? ◾ 61 There are two main approaches for representing color: by adding colors and by masking colors. Why are two approaches used, and how do these approaches work? To understand the display of color in a document, let us consider how color is generated on a monitor and how color is printed in a printer. As we shall see, the mechanics of color generation for these devices yield rather different perspectives. Color monitors work by adding together light of different colors. Normally, each dot on the screen includes a mechanism to generate a red color, a green color, and a blue color. Think of three light bulbs placed next to each other at the location of a pixel. If we turn on just the red light, of course, we see red. If we turn on both the red and green lights with equal intensity, we see yellow as the combined result. Table 3.1 shows how some combinations of lights may yield various colors.

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  eBook - PDF

  Exploration of computer graphics

  • Adele Kuzmiakova(Author)
  • 2023(Publication Date)
  • Arcler Press

    (Publisher)

  For example, in a ray tracer, you may build code to display ray trees so you can see which routes contributed to a pixel, or you might construct plots in an image resampling procedure to show all the spots where samples are being obtained from the input. Whenever it comes time to improve your software, the work invested in creating code to see its inner state pays off in a greater knowledge of its behavior (Dyer, 1982). 1.9. PAINTING AND DRAWING This book focuses on 3D graphics, with the majority of the effort going into creating a 3D model of a scene. In virtually all circumstances, however, a computer graphics project will result in a 2D image. Direct generation and modification of 2D pictures is, obviously, a significant issue in and of itself. Furthermore, many concepts are transferable from 2 to 3 dimensions. As a result, it makes sense, to begin, with 2D graphics (Yun-Jie and Hui-Xiang, 1991). Pixels are the elements that make up a picture on a computer screen. A rectangular grid of pixels is organized in columns and rows on the screen. Because the pixels are so little, it is difficult to discern them separately. In reality, they become nearly undetectable on many ultra-high-resolution monitors. Every pixel may only display one color at a time. Most modern screens employ 24-bit color, which allows a color to be described using three 8-bit values that represent the color’s blue, green, and red levels. Every color that may be seen on a screen is composed of a mix of such three “primary” hues. Other formats, like grayscale, are feasible, in which each pixel is a different shade of gray and the pixel color is determined by a single integer that specifies the gray level on a black-to-white scale. Commonly, 256 hues of gray have been utilized (Pang et al., 1987). Initial computer screens employed indexed color, which might only show a limited number of colors, generally 256 or 16.

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  eBook - PDF

  Digital Multimedia

  • Nigel Chapman, Jenny Chapman(Authors)
  • 2014(Publication Date)
  • Wiley

    (Publisher)

  4 Resolutio ■ n Device Resolution. Image Resolution. Resampling. Image Compressio ■ n Lossless Image Compression. JPEG Compression. JPEG2000. File Format ■ s GIF and PNG. JPEG Files. Other Formats. Metadata. Image Manipulatio ■ n Image Manipulation Software. Layers. Selections, Masks and Alpha Channels. Pixel Point Processing. Pixel Group Processing. 4 Bitmapped Images 102 BITMAPPED IMAGES C onceptually, bitmapped images are much simpler than vector graphics. There is no need for any mathematical modelling of shapes; we merely record a value repre- senting the colour of each pixel in the image. Images are not restricted to those that can be constructed from a small repertoire of drawing primitives, so a much broader range of visual possibilities is available. Above all, bitmapped representations can be used to record photographs. The main cost for this simplicity and range is in the potentially large size of image files and the difficulty of identifying objects within an image for the purposes of editing and transformation. It is rarely necessary to compute and assign the colour value for each pixel explicitly. Many images are created from external sources, such as digital cameras or scanners, which use hardware to sense colours and create the array of values. For creating original digital images, programs such as Painter allow visual artists to use familiar techniques (at least metaphorically) to paint images. Bitmapped images can also be created by rendering vectors. Resolution The concept of resolution is a simple one, but the different ways in which the word is used can be confusing. Resolution is a measure of how finely a device approximates continuous images using finite pixels. It is thus closely related to sampling, and some of the ideas about sampling rates introduced in Chapter 2 are relevant to the way resolution affects the appearance of images. Device Resolution Originally, a device’s resolution was a measure of its ability to distinguish fine detail.

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