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A number of factors can affect the resulting quality of a reduced color image. Perhaps the most important is the color palette used in the reduced image. For example, an original image (Figure 1) can be reduced to the secure web palette of 216 colors. If the original pixel colors are simply translated into the available color closest to the palette, there is no dithering (Figure 2). Typically, however, this approach results in flat areas (contours) and loss of detail, and can produce spots of color that are significantly different from the original. Shaded or gradient areas can create bands of color that can be annoying. The dithering application can help minimize these visual artifacts and usually results in a better representation of the original (Figure 3). Dithering helps reduce color scratches and flatness. In a groundbreaking paper published in the AES Journal, Lipshitz and Vanderkooy pointed out that different types of noise with different probability density functions (PDF) behave differently when used as dithering signals[13], and suggested optimal dithering signal levels for audio.

Gaussian noise requires a higher additional noise level to completely eliminate distortion than rectangular or triangular distribution noise. Triangular distributed noise also minimizes noise modulation – audible changes in the volume level of residual noise behind soft music that draw attention to the noise. [14] Noise shaping is a filtering process that shapes the spectral energy of the quantization error, usually to defuse the frequencies at which the ear is most sensitive or to completely separate the signal and noise bands. When dithering is used, its final spectrum depends on whether it is added inside or outside the feedback loop of the old noise. Inside, dithering is treated as part of the error signal and formed with the actual quantization error. Externally, dithering is treated as part of the original signal and linearized quantization without forming itself. In this case, the final noise floor is the sum of the flat dithering spectrum and the quantification noise formed. Although real-world noise shaping usually involves loop dithering, it is also possible to use it without adding dithering, in which case quantization errors are evident at low signal levels.

Most images are distorted in a diffuse or random pattern to reduce the difficult transition from one color to another. But dithering also reduces the overall sharpness of an image and often results in a striking grainy pattern in the image. This loss of image detail is especially evident when color photos are reduced to the browser-secured 216-color palette: To Help N.I.N.A. To communicate with PHD2 and control operations such as dithering and receiving guide telemetry, PHD2`s internal server must be enabled. To enable PHD2`s internal server, go to the PHD2 Tools menu and make sure enable server is selected. The desired type of dithering is based on the connected device in the Equipment tab > Guide. Figure 2. Original image with the web-safe color palette without dithering. Note the large flat surfaces and the loss of detail. Dithering is analogous to the halftone technique used in printing.

For this reason, the term dithering is sometimes used as a synonym for the term halftoning, especially in conjunction with digital printing. A common application of dithering is to display graphics with a wider color gamut more accurately than the display hardware can display. For example, dithering can be used to display a photographic image with millions of colors on video hardware that can only display 256 colors at a time. The 256 available colors would be used to create a distorted approximation of the original image. Without procrastinating too much, the colors of the original image would be quantified to the nearest available color, resulting in a displayed image that represents a misrepresentation of the original. Rectangular Probability Density Function (RPDF) Dithering noise has a uniform distribution; Each value in the specified range has the same probability of occurrence. A common use of Dither is to convert a grayscale image to black and white, so that the density of black dots in the new image is approximately equal to the average gray value in the original. The Gaussian PDF has a normal distribution. The probability relationship of the results follows a bell-shaped or Gaussian curve typical of dithering generated by analog sources such as microphone preamplifiers. If the bit depth of a recording is large enough, this preamp noise is sufficient to attenuate the recording. Dither is used in many different fields where digital processing and analysis are used. These applications include systems that use digital signal processing, such as digital audio, digital video, digital photography, seismology, radar, and weather forecasting systems.

There is a saying of professional astronomers; “Procrastinate or die.” It may not be as bad for amateur astrophotography, but procrastination will greatly improve your images. Find out what my good friend Dylan has to say about dithering: Astro Photography Tool (APT for short) can communicate with various programs and guidance devices to monitor your self-guidance performance. This communication between the camera capture software and your devices is necessary to enable procrastination. The other widespread use of dithering in image processing is artistic. Programs like Photoshop allow photographers and graphic designers to add exciting nuances to their images. By applying different pattern overlays to images, you can create fun and unique images. You can even replace the colors for dithering by changing your palette in the color fill. A typical application is to change a black and white photo into an aged photo with raster and sepia tones, as shown below: One of the most important applications for dithering was to avoid streaks in a gradient or gradient. By mixing hues from a limited palette to simulate the original color, you shrink the file, creating a file that can be downloaded faster to your screen and/or computer. GIFs are a great example of image procrastination.

Smaller files require less bandwidth, which allows for faster transfer. In the early days of the Internet, procrastination was a web designer`s best friend. You can create more visually appealing websites while being user-friendly for slower data connections. Figure 3. Original image with web-safe color palette with Floyd Steinberg`s procrastination. Note that although the same palette is used, the dithering application gives a better representation of the original. I created this image of the Carina Nebula manually using an iOptron SkyGuider Pro mount. Graph 5. The depth of this image is reduced to an optimized palette of 16 colors without hesitation. The colors appear muted, and the ribbons are pronounced.

N.I.N.A. offers three different ways to perform dithering: Your camera control software does exactly what I did with the ST-4: it pauses the sequence of images between exposures and sends a dithering offset to the self-guidance program, which then passes the command to the Mount Control pilot, who moves the area. The Autoguider software captures the guide star again and starts guiding, and your camera`s control program then starts the next exposure. If the signal during the regime does not need to undergo additional processing – if it is dipped to its final result for distribution – then coloured dithering or noise shaping is appropriate. This can effectively reduce the audible noise level by bringing most of that noise into a frequency range where it is less critical. Fortunately, in today`s modern digital world, we can automate many processes in astrophotography. We use a computer to control the telescope mount, imaging camera and self-guide. The software that controls these different hardware elements allows them to communicate with each other to get the job done right. Programs such as AstroPhotography Tool, BackyardEOS or BackyardNIKON can work with PHD2 for self-guidance. You can also use Sequence Generator Pro with PHD2 or MetaGuide. High-end software including MaximDL integrates all these functions. Some liquid crystal displays use time dithering to achieve a similar effect.

By quickly changing the color value of each pixel between two approximate colors in the color space of the control panel, a display panel that only supports 18-bit colors (6 bits per channel) can display a 24-bit color image (8 bits per channel). [17] Example of a successful dithering after a failed settlement attempt Example of a failed settlement due to a timeout The second image is a smooth gradient where dithering was applied. The strip is no longer visible and produces a much smoother image.