Raster graphics Also called a bitmap or bitmap. It is a data file that represents a matrix of pixels (colored dots) called a raster. In this matrix the color of each pixel is individually defined and can be displayed on a monitor, paper or other display device.
The images on map bit is the usually defined by its height and width (in pixels) and color depth (in bits per pixel), which determines the number of different colors that can be stored in each single point, and therefore, to a large extent, the color quality of the image.
Raster images are used for photography and filming, while Vector images are used in graphic design. The vector graphics represent an image using simple geometric shapes such as polygons while the rasterized graphics represent them by storing the Color . A raster image cannot be very enlarged because it loses resolution and looks “pixelated”
Summary
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- 1 Color
- 2 Resolution
- 3 3D analogy
- 4 Formats
- 1 Bitmap formats
- 2 Metafile formats
- 3 More sophisticated formats
- 4 Graphic and image file formats
- 5 Raster graphics editor
- 1 Raster graphics editors vs. vector graphics editors
- 6 Common Features
- 7 Raster image processor
- 8 Steps of a RIP
- 9 Internal links
- 10 Sources
Color
Each point represented in the image must contain color information, represented in separate channels that represent the primary components of the color that is intended to be represented, in any color model, be it RGB , CMYK , LAB or any other available for its representation. To this information, we can add another channel that represents transparency with respect to the background of the image. In some cases, ( GIF ) the transparency channel has a single bit of information, that is, it can be represented as totally opaque or as totally transparent; in the most advanced ( PNG , TIFF), the transparency channel is a channel with the same depth as the rest of the color channels, with which hundreds, thousands or even millions of different levels of transparency can be obtained.
It is distinguished from vector graphics in that they store information in mathematical formulas . Raster graphics when enlarged begin to pixelize, that is, the constituent elements of the graphic are enlarged, and lose quality. Instead the vector graphics can be enlarged without limits.
Resolution
The quality of raster images is determined by the total number of pixels they possess (resolution) and the amount of information in each pixel (generally called color depth). For example, an image that stores 24 bits of information per pixel (which has been the standard for all screens since 1995) may more smoothly represent hues than an image that stores only 16 bits per pixel.
Similarly in terms of resolution, an image of 640 x 480 pixels (with a total of 307,200 constituent pixels) will be more rugged and pixelized compared to one of 1280 x 1024 (which has 1,310,720 constituent pixels).
Raster graphics need to be compressed because they often need a lot of data in order to store high-quality images. Some compression techniques, to achieve a smaller size, sacrifice image information to achieve their goal. This causes the image to lose quality and it cannot be recovered.
In a bitmap image its dimensions cannot be changed without noticeable quality loss. This disadvantage contrasts with the possibilities offered by vector graphics, which can easily adapt their resolution to that of any display device.
In any case, there is a greater loss when trying to increase the size of the image (increase the number of pixels per side) than when reducing it. Bitmap images are more practical for taking pictures or shooting scenes, while vector graphics are mostly used for representing geometric figures with defined parameters, making them useful for graphic design or text rendering.
Today’s computer displays typically display between 72 and 130 pixels per inch (dpi), and some printers print 2400 dots per inch (dpi) or more; Determining what is the best image resolution for a given printer can be quite complex, since the printed result may have more detail than the user can distinguish on the computer screen. Typically, a resolution of 150 to 300 dpi works well for 4-color (CMYK) printing. However, there is a mathematical formula that allows defining this resolution according to the printing substrate: lpi x 2 xfa / r = ppp Where lpp (lines per inch) is the reference to be used according to the substrate, for example: 150 lpi, if they are coated papers, 85 lpp for newspaper, etc. 2 is a factor based on the rasterization capacity of the scanner and fa / r is the enlargement or decrease in the image required. The formula can only be used as lpi x 2 = dpi.
3D analogy
In 3D (three-dimensional) infographics the concept of a flat pixel grid extends to a three-dimensional space made up of cubic bricks called voxels. In this case, there is a three-dimensional grid with elements (cubes) that contain the color information. Despite the fact that voxels are a powerful concept for treating bodies with complex shapes, they require a lot of memory to be stored. Consequently, when producing 3D images, 3D vector images are used more often.
Formats
Bitmap formats
Although there are literally dozens of different types of graphic file formats, only a few of them are in general use. Graphic file formats are divided into several categories such as raster, vector and metafile. Bitmap graphics is a non-scaling bitmap data structure. Vector graphics are used in scalable line drawings as clip-art that do not distort the image much. Metafile graphic formats contain raster and vector data in a single image file. Below is a summary of the most common graphic file formats.
Bitmap graphics is used to store uncompressed bitmap data, preserving the quality of a raster graphic. They are best suited for storing high quality images even though they also take up a lot of space. They contain an unmodified pixel-by-pixel map of the entire image map. The most widely used uncompressed bitmap format on Windows-based computers is BMP, although TIFF and TGA are also common. The JPG format is by far the most widely used compressed bitmap format.
Metafile Formats
Most of the more sophisticated graphics editing software supports raster and vector graphics editing. The data is stored in a metafile format that comprises both types of graphics. The most common metafile format used in Windows is the native “Windows Metafile Format” or “WMF” for short. The Adobe PDF file format, although not really a standard graphics format, contains images, text and vectors, although it can also be used exclusively for graphics storage.
More sophisticated formats
Programs like Corel Paint Shop Pro, CorelDRAW and Adobe Photoshop have their own advanced formats to hold all kinds of graphic data. The native format of the latter is “PSD”, which has become one of the most common advanced graphics formats and is now compatible with many competing applications, at least in part. Such formats can contain graphics and raster data in the form of separate editable layers.
Graphic and image file formats
- Bitmap graphics formats (rasterized)
art, .bmp, .cin, .cpt, .dpx, .exr, .fpx, .gif, .iff, .ilbm, .lbm, .jpeg, .jpg, .jpg2, .jp2, .mng, .pbm, .pcd, .pcx, .png, .ppm, .psd, .sgi ,,. rgb, .rgba, .int, .inta, .bw, .tga, .tpic, .tiff, tif, .raw, .wbmp , .xbm, .xcf, .xpm
- Vector graphics formats
ai, .cdr, .cgm, .dxf, .dwg, .fh, .fla, .ps, .svg, .svgz, .swf, .sxd, .wmf, .xalm, .xar
- Raster and vector formats
eps, .pdf, .pict, .pct ,. pic, .px, .pgm, .psp
- Metafile formats
eps, .pict
Raster graphics editor
A raster graphics editor is an application that allows the user to interactively create and edit raster graphics images and store them on the computer in a graphic file format, such as JPEG, PNG, GIF, and TIFF. To view images, it is generally preferable to use an image viewer rather than a raster graphics editor. Some editors are specifically designed for photorealistic image editing, such as the popular Adobe Photoshop, while others are more geared toward artistic illustrations, such as Adobe Fireworks.
Raster graphics editors vs vector graphics editors
Often editors vector graphics and raster graphics editors contrast, and features complement each other .
Vector graphics editors are best for graphic design, blueprint design, typography, logos, art illustrations, technical illustrations, layout, and flowcharts. Raster graphics editors are best suited for photo manipulation, photorealistic illustrations, collage, and hand-drawn illustrations using a digitizer tablet.
Many illustrators today use Corel Photo-Paint and Adobe Photoshop to create all kinds of illustrations. Recent versions of raster graphics editors like GIMP and Photoshop support vector tools and vector graphics editors like CorelDRAW, Adobe Illustrator, Xara Xtreme, Adobe Fireworks, Inkscape or SK1 are slowly adopting tools and techniques that ever they were exclusive to raster graphics editors (such as blurring).
Common features
- Select regions to edit.
- Draw lines with brushes of different colors, sizes, shapes and pressure.
- Fill a region with a color solor, a color gradient, or a texture.
- Select a color using different color models (for example RGB, HSV), or using a color picker.
- Write text in different font styles.
- Remove all kinds of imperfections in the photos, such as wrinkles, scratches and dirt.
- Combine layers, each with a different job.
- Edit and convert between different color models.
- Apply filters to achieve various effects.
- Convert between different graphic file formats.
Some editors are specifically designed for photorealistic image editing, such as the popular Adobe Photoshop, while others are more geared toward artistic illustrations, such as Adobe Fireworks.
Raster Image Processor
A raster image processor, or RIP, is a device that is used in printing systems to produce a bitmap image. Subsequently, the bitmap generated by the processor is sent to a printing device. The data entry in the RIP can be a page generated in a high-level page description language such as PostScript, PDF (Portable Acronym English) or XPS. It can also be another bitmap of a device whose output is sent to the RIP input. Ultimately, the RIP device applies interpolation and smoothing algorithms on the input bitmap to generate the output bitmap.
The purpose of the processing for which a RIP has been conceived is to achieve a high resolution raster image from digital vector information. Initially, RIP devices were a stage of the hardware electronics that received the page description through an interface (generally RS232) and generated an output that was later used to enable or disable each pixel in real time from the device. output such as the scanner of a photolith imager.
What’s more, a RIP can be implemented in a software component of the operating system or as firmware executed on a microprocessor inside the printer. Ghostscript and GhostPCL are examples of RIPs software. Each Postscript printer contains a RIP in its firmware. Newer RIPs are backward compatible with photosetters so they are capable of supporting older languages.
Steps of a RIP
- This is the step where the supported page description language is transformed into a representation of a particular page. Many RIPs process pages with such intensity that the normal operation of the machine is only for the current page, that is, only one page is processed at a time. Once the page has been generated the next one is processed.
- Process through which the particular internal representation is transformed into a continuous-tone bitmap. It should be noted that in practice rendering and rendering are done together quite frequently. Simple languages (mostly older ones) were designed to work with minimal hardware requirements, so they tend to run rendering directly.
- To print, a continuous-tone bitmap must be pre-transformed into a mid-tone bitmap (dot pattern). There are two methods or types for this step. The projection by modification in amplitude (AM or Amplitude Modification) and the stochastic projection or by modulation in frequency (FM or Frecuency Modulation). In the AM projection, the variation in the size of the points depends on the density of the object and its tonal values. The dots are placed on a fixed grid but are larger if they correspond to a high-density image area. In FM projection, the size of the dots always remains constant and they are placed in a random order to create lighter or darker image areas. The location of the points, and the density of these,
RIPs are used in laser printers to communicate raster images to the printer’s scanning laser.
