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About Image Editing. Teppo Räisänen LIIKE/OAMK 2011. What Is Image Editing?. Manipulation of digital images – from simple operations to complicated edits Creation of new images Image editing has been done before computers. What Is Image Editing?. Digital image formats can be divided into
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About Image Editing Teppo Räisänen LIIKE/OAMK 2011
What Is Image Editing? • Manipulation of digital images – from simple operations to complicated edits • Creation of new images • Image editing has been done before computers
What Is Image Editing? • Digital image formats can be divided into • Vector graphics • Bitmap graphics
Vector Graphics • Image is stored in a form of mathematical algorithms • The image files are typically smaller than of bitmap images • The images are easily scalable • Best suited for image objects with clear borders and colors
Vector Image Formats AI Adobe Illustrator CDR CorelDraw DRW Micrografx Draw DXF Autocad DWG Autocad EPS Encapsulated PostScript FH8 Freehand HGL Hp Graphics Language PS Postscript WMF Windows Metafile
Bitmap Graphics • The image file consists of pixel level color information • Editing a bitmap = affecting to the pixel color values • Typically bitmaps are used for • photograph editing • scanned images • Scaling upwards will result in lessening of the image quality
The Basic Qualities of Bitmap Images Five Basic Qualities: • Pixel Size • Pixel Coordinates • Resolution (ppi) • Color Model (e.g. RGB / CMYK) • Color Depth (bit)
Pixel • A single pixel is always of matte color • Within a single image it’s all pixels are of same size • Single pixels should be small enough not to be observed separately • If the pixels are too big = pixelisation
Resolution • ppi (=pixels per inch) • for scanned, self-drawn or digital camera images • amount of pixels / inch of an image • dpi (=dots per inch) • the physical accuracy of scanners and printing devices
RGB • Red, green & blue. • Three values are stored from each pixel of the image • Typical color model of light emitting devices • RGB is used for the images of Web pages
CMYK • cyan, magenta, yellow ja black. • Color model for printed images • Editors like Photoshop handle changes of color models automatically • Often colors are set using computer display (and rgb) and conversion to cmyk happens only when printing an image
Bitmap Image Formats BMP = Windows image format • Large image files • No information about the image’s printing size can be stored GIF = CompuServe Graphics Interchange Format • Compressed image format • Used widely for Web graphics • Not good for photographs or images with gradient colors • GIF can contain animations
Bitmap Image Formats JPEG, JPG = Joint Phographics Experts Group • Adjustable compression rate • Information about resolution can be saved in the image file • Used widely for Web graphics • Typical file format of e.g. cameras of mobile phones PNG = Portable Network Graphics • Developed to be used for Web graphics • Supports transparency
Bitmap Image Formats PSD = Photoshop format • Information about layers, masking etc. • Large image files TIFF = Tagged Image File Format • Compressed/uncompressed • Very large image files • Compatible with many platforms & applications
Bitmap Image Formats • There are two types of image file compression algorithms: • Lossless and lossy
Bitmap Image Formats • Lossless compression algorithms • Reduce file size without losing image quality • Thus images are are not compressed into as small a file as a lossy compression file. • When image quality is valued above file size, lossless algorithms are typically chosen. • Examples: PNG, TIFF
Bitmap Image Formats • Lossy compression algorithms • Take advantage of the inherent limitations of the human eye and discard invisible information. • Most lossy compression algorithms allow for variable quality levels (compression) and as these levels are increased, file size is reduced. • At the highest compression levels, image deterioration becomes noticeable as "compression artifacting". • Examples: JPG
Rasterizing • = Conversion from a vector shape to bitmap information • E.g. PhotoShop uses vector shapes for many operations • To be able to perform some edits rasterizing is often necessary
Image File Size • Digital image files may be of hundreds of megabytes • Especially Web graphics files should be small sized • Eventually the purpose of a file directs the appropriate file format and size
Amount of Pixels • Cropping of unused parts of an image results in faster editing
Resolution • 2X resolution = 4X amount of pixels
Examples of Bitmap Operations • Contrast optimization • Color balance adjustments • Resizing of an image • Cropping • Rotating and skewing • Blurring and sharpening • Effects (Filters)
