The image processing is the change of photos , negatives , slides or digital images. It is to be distinguished from image processing , which is used to process the content of images. Image processing is often used to eliminate errors that can occur during photography or other image capture. These include, for example, overexposure and underexposure , blurring , poor contrast , image noise , red-eye effect and converging lines . Due to these errors, images often appear too dark, too light, too blurred or otherwise deficient. The causes can be technical problems or poor quality of the recording devices ( digital cameras , lenses , scanners ), their incorrect operation as well as unfavorable working conditions or inadequate templates. The two images on the right show some options for image processing: The upper image looks overexposed, has a color cast , the text is blurred, the object at the top shows a light reflex and lies outside the center. The lower, corrected, now color-pure image, on the other hand, looks much clearer and clearer. Because the subject of the picture is emphasized, because it is larger, rectified and in the middle of the picture, the format has been slightly adjusted in height.
Types of image editing
In the digital image processing is the computerized processing of digital images, usually raster graphics , mostly photos or scanned documents. The necessary hardware and software are relatively inexpensive, so this type of image processing is widespread. The possibilities of digital image processing are extremely diverse and often only limited by the lack of knowledge of the processor.
The traditional image editing includes photographs, negatives and Diabearbeitung. Special equipment, materials, chemicals and knowledge are required for this type of image processing. This type of image processing is a domain for specialists. The possibilities are very diverse; Due to the often very large effort, however, no longer makes economic sense today.
The hybrid image processing includes methods of traditional and digital imaging and was in the 1990s developed. While the film is being exposed in the enlarger , there is a special transparent pane between the film and the photo. This disk can be made partially opaque by means of an electric current. In a fraction of a second, it can be re-exposed, dodged or unsharp masked . Nowadays this technique is used on a large scale in the production of paper prints from negative film.
Today's digital form of image processing emerged from various forerunners: the following main areas can be named as examples:
- Repro technology (typical for this are all forms of contrast change )
- Photography ( laboratory techniques are typical )
- Printing technology (typical are color separation , rasterization )
- TV technology (typical are color channels and mounting methods)
- Computer graphics ( vector-based processing is typical )
All areas have left their own mark, for example:
- from repro technology : unsharp masking
- from photography : the filters
- from printing technology : the unit of measurement "inch" ( found in "ppi", "dpi" )
- from television technology : the alpha channels
- from computer graphics : the path tools
Today's form of digital image processing is still very young. Due to the traces of the many forerunners, it contains numerous terms that mean the same thing. One example is the (partial) coloring of black and white images. The following terms can be found in Wikipedia:
- Coloring , the colloquial term
- Toning , a term used in photo laboratory technology
- Keying , a term used in television and video technology
Same terms that mean different things:
- Example “printing”: In photography, this means an (absolutely) raster-free exposure , while printing technology means a raster printing process.
Terms that are not unique:
- Example " dpi ": In the application software of a scanner , this means the pixel (per inch), while in printing technology it is the raster point (four raster points are usually formed from one pixel).
Numerous reference works, even textbooks for current photography training, contain this ambiguity. There are also numerous terms in Wikipedia that are not uniformly defined (some examples are linked in this chapter).
The software used in the field of image processing is discussed in the article graphics software .
Some possibilities of digital image processing
The software used to process the image is called an image processing program . It offers numerous editing functions, most of which are located in a program menu, a toolbar or a toolbar. Examples for this are:
- Dodging and burning: By the Dodge and Burn (engl. Dodge and Burn), the exposure corrected.
- Select: Certain areas of the image can, for example, be rectangular, circular or partially marked and thereby selected. These areas can then be edited separately from other image sections. There are various selection tools for making selections, on the one hand geometrically specific, such as a rectangle, an ellipse, etc., and on the other hand specific aids such as Lasso tools or magic wand.
- Automatic corrections: Image editing programs offer automatic corrections for beginners and newcomers to image processing. They are used to correct various areas, such as contrast, color and tone value , at the push of a button. In contrast to the manual correction, the results of the automatic correction are to be viewed rather soberly.
- Beauty retouching is the extreme stylization of portraits - various techniques are used, mainly digital retouching techniques.
- Exposure correction: With various tools of the exposure correction overexposed or underexposed images can be corrected. The exposure correction takes place globally via brightness and contrast , via the gradation curve (tonal value correction) or partially by dodging and post-exposure .
- Colorkey: describes the colored highlighting of picture elements in a black and white picture.
- File format: Conversion or storage in a specific graphic format . One differentiates u. a. the JFIF , PNG , GIF , TIFF or JPEG2000 format. The PSD or XCF format is suitable for storing layers, masks and channels .
- Rotate: By rotating an image, recording errors can be eliminated or special effects can be achieved. Slight turning is particularly advisable if the horizon is “crooked”.
- Layers : Different picture elements can be arranged one above the other like on transparencies. The individual elements are arranged on different levels and processed individually. Layers can be locked to prevent accidental editing or deletion. Swapping layers moves objects to the foreground or background.
- Exif information: The display of Exif information such as the recording time, digital camera manufacturer and digital camera data. Other metadata , such as the IPTC-IIM standard , can also be displayed.
- Colors: Colors play an important role in image processing. The hue can be changed, the color saturation adjusted and color casts removed. On the other hand, the colors can also be withdrawn from an image, for example to create black and white images. When it comes to colors, a distinction is made between subtractive and additive color mixing . Here are color models and color spaces like RGB , CMYK , L * a * b and HSB describing colors. The cross effect describes a subsequent shift in the color spectrum .
- Color mode and color depth: You can convert an image into a desired color mode or image mode. A distinction is made between the modes: bitmap, grayscale, duplex, indexed colors, RGB, Lab and CMYK. Depending on the color mode, you get a different color depth . In terms of color depth, a distinction is made between true color , high color and indexed colors , but also between grayscale and black and white.
- Filters: Images can be processed and altered with a variety of graphic filters : Blur and sharpness filters (e.g. edge sharpening ) are often used . Filters with more artistic effects are, for example, relief effects, lighting effects, shadow effects, and soft focus. There is also the option of expanding graphic filters with plug-ins .
- Shapes: Used to produce geometric objects such as rectangles, ellipses or polygons; but also for creating pattern shapes such as speech bubbles, symbols, etc.
- Photo montage: In photo montage , also known as “composing”, several images are put together to form a kind of composition. For example, individual picture objects can be selected and copied into another picture. See also photo collage .
- Photo mosaic: In photo mosaic , an image is created from many photos placed side by side.
- Cut out: Unusable image sections are removed to emphasize an object. The cropping of images is one of the essential tasks of image processing.
- Fill: The fill tool is used to fill an entire image or just a section of an image with a desired color.
- Gamma correction: With a gamma correction , the lighting conditions and the color tones are changed.
- Gradation: The contrast and brightness are changed with a gradation curve .
- Histogram: A histogram is used to display the brightness spectrum of an image. That plays u. a. plays an important role in tonal value correction .
- Invert: When inverting , the colors are reversed.
- Channels: A color channel indicates that each basic color uses a color channel. In CMYK mode there are four channels (cyan, magenta, yellow and black) and in RGB the basic colors red, green and blue. A distinction is also made between alpha channels ; selections and masks can be saved here.
- Tilt: tilting can remove perspective errors in an image.
- Coloring: When coloring , images or image sections are changed in color; In contrast to the color key, grayscale images are usually colored afterwards.
- Conversion of image files into various file formats or graphic formats . See also file format.
- Copy stamp: Used to correct blemishes and to transfer image sections to other areas. Used heavily in portrait retouching.
- Correction of brightness , contrast and tone value (also for creating high-key or low-key characters)
- Lasso: The lasso is used to select areas of the image.
- Macros: A sequence of processing steps can be saved as a macro so that it can be applied to multiple images as often as required.
- Painting : One of the most basic functions of image editing programs is the ability to paint. Painting techniques are simulated with the help of different brushes. A distinction should be made between painting and drawing. Pixels are created when painting, but not when drawing. Paths are therefore used for drawing; vector elements can be created with them.
- Masking: Masking selects specific areas to protect them from editing. The mask can be expanded with the brush in mask mode or reduced with the eraser. Errors can easily be undone in mask mode.
- Monochrome: The creation of monochrome images can be carried out easily with the help of an image processing program.
- Panorama: For still images, such as a large landscape, can be a panoramic image to create. There is also special stitching software for this.
- Paths: Image editing programs can also be used to draw vector elements. Paths are used here to create simple vector elements. If you want to create more complex drawings, you should use vector graphics programs. You should also keep in mind that when you draw, in contrast to painting with a brush, no pixels are created.
- Brush : The brush has developed into a universal painting tool: size and brush tip can be selected, a color can be chosen or filled with a pattern. The brush is particularly used in digital painting .
- Pipette: The pipette is used for color determination and color pick-up.
- Eraser: Removing image information with different eraser tips.
- Undo: Work steps that allow it can be undone with the Undo function.
- Sharpen: When sharpening is sharpness of an image or individual image areas increased. The dominant method is called unsharp masking .
- Scaling : Images can be enlarged or reduced by various methods.
- Solarization: With electronic solarization , the colors of pixels whose brightness is above an adjustable limit value are inverted.
- Mirroring: Mirroring (horizontal or vertical) is often used to correct scanned negatives or to fit images into a layout.
- Batch processing: Functions and / or macros are automatically carried out in several image files. This function is particularly useful for digital photo albums. So z. B. the image size, the resolution, etc. can be changed, which saves a lot of work compared to individual editing.
- Texts: A text tool can be used to create a wide variety of texts on an image, with many text effects such as relief etc.
- Toning: A black and white image is colored. The best known tone is sepia .
- Tonal value correction: The tonal range can be corrected with a tonal value correction. The histogram is used as an aid by showing the light and dark areas. The brightness, contrast and color saturation can then be specifically corrected.
- Change in file size ( image compression ), resolution or image resolution , for example for using images on the Internet.
- History: With gradients you create color transitions.
- Blur: With blur , the image or individual parts of the image are blurred, for example to cover an unsuitable background. However, blurring can also be used to create effects such as motion blur .
- Magic Wand: Highlighting tool that selects all pixels that are adjacent to the clicked pixel and have a similar hue and brightness. Often used to select the background.
- Drawing: When drawing, in contrast to painting, no pixels are created, but vectors. Here paths are used to create vector elements.
- Zoom: For many processing steps it is necessary to move closer to the object, for example to remove image errors.
Areas of application for image processing
Digital image editing has become widespread due to the capabilities of digital photography , which allows for quick photography and transfer of the images to the PC. Many image processing programs (" graphics software ") are tailored to home users by offering, among other things, simplified correction options. In the professional sector, image processing is used by photographers, designers and media designers in the desktop publishing sector and in prepress . The images changed in the image processing are published in publications - print and digital media - of all kinds, for example in magazines, catalogs and books.
Image processing can also be used specifically for photo manipulation . Typical examples include editing faces to remove wrinkles and other "blemishes" and removing unwanted people from an image. The boundaries between legitimate image processing and illegitimate photo manipulation are fluid; an assessment must be made on a case-by-case basis.