Archiv für 2007

Resolution is a term that expresses how well the graphic presentation shows the spatial details in a picture. It is a measure of the fineness of the picture elements. Digital images consist of a large number of picture elements (pixels) in rows and columns, each with a defined color. A pixel is one of many cells that form a picture. An image may extend X pixels from left to right and Y pixels from top to bottom, and contain X times Y pixels. A user has some latitude in how many pixels are used to display a certain picture. For example, the monitor has a few settings for selecting the full screen presentation. The most commonly used resolution setting is 800 X 600 pixels. If every pixel is actually seen (including the corners of the image), there will be 480,000 of them.
Modern digital cameras have frame sizes of 2 megapixels or 4 megapixels, so the need to re-size and crop these images becomes important. If a full-frame image is received as an attachment, the recipient may see only the upper-left corner of the image unless they do some scrolling. Then they may like to make the picture small enough so that it is more readily viewable without scrolling.
Re-sizing and cropping are topics discussed later.
Most viewing software applications (and printers) display the typical image formats BMP, JPG, and GIF at 96 pixels per lineal inch. If a user wishes to stretch a given image file for presentation or for printing, they will get no better resolution by zooming in to make the image bigger. If an image file is modified by stretching or shrinking the overall dimensions, the software must find a means for making the picture information accommodate a newly formed matrix of pixel sizes or pixel count. If the pixel count changes, the picture must retain its basic character, yet the color assignments of the new set of pixels is not the same as the original picture. The software must have algorithms that account for these requirements. The ability of software to accommodate these zoom requirements varies from one software package to another. A test of the quality of image-modifying software is to note if there is significant degradation of an image if it undergoes a series of changes. One of the more noticeable degradations due to zooming will appear in the quality of the text. A particular font type and size will have specific pixel cells blackened.
If you depart from the resolution in which the text was acquired, some software will have a tough time keeping the boundaries between black and white organized so the stroke width and precise shape of the text characters are maintained or simulated. A zoom-type feature may be used in the MS Paint application by commanding Image|Stretch/Skew. When the Stretch and Skew dialog box appears, you will note that there are small highlighted windows opposite the words Horizontal and Vertical in the upper (Stretch) panel which each say 100%. To shrink the picture to half of the original image dimensions, you do so in two steps.
First, click (dropping a cursor) in the Horizontal (small) window, and replace the 100% with 50 %, and click on Okay.
Then do the same for the 100% value in the Vertical (small) window, and click on Okay.
Scanner software generally has choices of scan resolution, as well as black and white vs. color, and a further determination of gray scale or simply black OR white coding when choosing black and white. The latter distinction is important when choosing whether you need two levels (one bit) of gray (either black OR white) or many levels (gray scale), which affords a more accurate rendition of the source material. Most often, you will find that the scanner software offers about five default settings for making these selections, and the means for making custom settings which depart from the default values. A large picture will produce a large image file, and settings that provide more picture details will make that file even bigger. The temporary image format used in scanner software and in image conversion software has no compression (i.e., all picture information is defined within each presented pixel). Thus, the user should note that it takes time for a slow computer to compile all the necessary data to form and to reformat this image if an unusually large, detailed image is being used. In fact, users should be aware that limitations of computer processing speed may not be apparent until you use large media files like a large color photos with high resolution. A user should be judicious in the choice of the scanner settings to make an image file having suitable spatial resolution and color resolution (the fineness of allowed step changes in the color palette) so that the selected resources are appropriate for the end result. Another image format is available that provides for more than 96 dpi resolution. Although the scanner software can accommodate resolutions that exceed 300 dpi, the user may wish to transfer that file to another computer which doesnt have the same scanner software. The format most often used for this purpose is TIF or TIFF. The TIF format provides for resolutions of 300 dpi, or other values which may be set when encoding the file. Also, it will encode either as uncompressed or compressed (JPG and LZW are compression options). The software application needed for creating a TIF file is (Kodak) Imaging, which is automatically installed with modern versions of Windows. Like MS Paint, Imaging will accept images from a clipboard, but you must define the spatial resolution and the color depth unless you are willing to accept the default settings. Imaging can be used for pictures of higher resolution than MS Paint, as it supports spatial resolutions greater than 96 dpi.
A user can copy or export scanned high-resolution images to JPG , GIF, or BMP formats, but the picture dimensions will increase to match the defined 96 dpi for these formats. If images are exported into TIFF format in Imaging with a resolution that matches that of the image exported from the scanner software, the dimensions wont change. The JPG and GIF formats have become standards for use on the internet, as they are able to reduce file sizes while preserving picture details. This is accomplished with the use of sophisticated algorithms that make choices about the picture elements (pixels) whose color definition dont change from the one which precedes it in the defined sequence of forming the pixels into the file.
In this sense, the algorithm votes out the data associated with certain pixels if there is no change from its preceding neighbor. In the viewer software, its algorithm has the ability to reformulate the original image in the absence of the data for those pixels whose color data was voted out. Also, web browsers will present files in JPG and GIF formats, while many web browsers may not present some of the other formats.
JPG file creation depends on a quality selection, often made by the user, in which the user makes a trade-off between the requirements for retaining image quality, and the resultant file size. Thus, a user can make a file with less than 100% quality retention if a smaller file size is desired. A JPG file is most often selected if the picture contains subtle shadings of color, and a small file size is desired. A JPG quality factor of 70% is often acceptable, as it represents a good trade-off between picture quality and file size. A GIF file is often chosen for tables, figures, cartoons, clip art, etc., where few shades of color are present. Choosing the GIF format for this kind of picture often results in a smaller file than a JPG file would provide. GIF is often used for the collection of small image insets which are placed on a web page. If a GIF file of appreciable dimension is shown in the top half of a web home page (so a visitor will see the image form on their screen), the visitor may notice that this image forms in a way which may seem distracting, since the picture elements form in cells much bigger than a single pixel, and these cells become progressively smaller as the fully resolved image takes form. This effect usually is not noted in GIF files of small dimension.