Formats and compression methods of GIF in Photoshop CS

[Frieda]

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I am not having enough knowledge about the Photoshop CS. So thought to take some information from you guys about it. I am recently started working with the Photoshop CS, and getting confused with the formats and compression methods that are used in Photoshop CS. I am here to get some notes about the formats and compression methods of GIF in Photoshop CS. I am sure that somebody will from your side will help me soon.

[Abraham.J]

The panel optimization for GIF, the most commonly used for the web, is rich in features. The following are some details of it :

• transparency: enables or disables the alpha channel of the GIF file, if the channel is enabled and the image contains transparent areas, they are filled with a color of Alone.
• Alone: You can choose the color of Alone (see Alone JPEG transparency and the previous option), if transparency is enabled, and you choose the same to give a glow to the image, the image boundaries are drawn with the color halo .
• Interlaced: interlaced GIF file is subjected to a progressive rendering of the browser, usually the image is fully rendered, but incomprehensible to improve the ability to download. By choosing this option, the weight of the image will be slightly increased.

[Nihar Khan]

You should also know about the compression algorithms. The most interesting part of the saving in GIF is undoubtedly the choice of the compression algorithm best suits the needs of the case. The drop-down menu allows us to select the compression:

• Perceptual: Compress the image by choosing colors that make up among those to which the human eye is most sensitive.
• Selective perception similar to compression, which also uses colors to the eye is sensitive, however, preferring those closest to the web-safe colors, and is definitely the best tuning option in most cases.
• Adaptive: it analyzes the image and recognize the colors applicants samplers and returning an image with fewer colors. Ideal for monochrome images or small number of colors is not always advisable for the web.
• Restrictive (Web): approximates websafe all colors to the palette. For websafe is a set of 216 colors that appear the same way on different browsers. If a color is not selected websafe, will be converted to color websafe closer.
• Custom: exclusive of any default compression algorithm, according to rescue the options and functions that we choose and use the remaining drop-down menu and slider
• White / Black: converting file colors in B / N. Gradients are approximated by dithering algorithms
• Grayscale: Convert color to grayscale files (desaturation).
• MacOS: suitable colors than ideal for viewing on a Mac
• Windows: right colors than ideal for viewing on Windows / Unix

[spuff]

Next to the drop-down menu of compression algorithms is an icon already seen before, which allows access to the mask optimization of the file on the texts and vector shapes or use of a specific channel. Loss factor: it is possible to have a loss of definition up to 50% by weight of the image. While the JPEG format uses the optical mixture, placing the pixels in the typical form in "blocks" the influence GIF image using the same principle but by mixing together the colors of individual pixels and reducing the quantity. If the Interlaced option is enabled, you can not change the loss factor. While talking about the number of colors, it is always appropriate when you intend to use the GIF format, change when you save the number of colors, if only to observe the changes in the image: images often consist of a number of colors below current settings, sometimes, drastically decreasing the number of colors, the image suffers considerable loss of definition. You can also make a number of custom colors by simply clicking on the box.

[Neil'o]

Dithering is the effect with which you can mix colors alternating sequences close of pixels of different colors. For example, to get a rose, you can switch to white pixels red pixels. The mixture can be achieved in different ways:

• Distribution: distributes the pixels in an irregular manner, softening edges and colors, making the mixture more natural, more random. By using the error diffusion dithering is to choose the intensity of the combo box using the "percentage of dithering."
• Pattern: the colors are arranged in a precise plots in alternating colors, you can not change the percentage of dither.
• Disorder: is an algorithm for blending with optical noise, colors arranged in random order as if the video image was subject to interference.

If the GIF image to be optimized has transparent areas, there is the possibility of applying the boundary zones between transparency in Dither and color pixels. GIF images do not have the translucency and contain only fully opaque pixels or fully transparent. Dithering does this by placing the colored pixels of the boundary areas in the plots that simulate transparency.

[Zeverto]

Imagine having to save this image to a web page that has a black background, the images that follow are to be regarded as transparent images placed in the background as proposed, if they look at the plot obtained in the simulation of translucency. These images are also equipped with a red halo: it's not the best solution to merge our figure in a black background but will use it to better identify patterns of dithering. Cursor Blocking Web function is a measure of the percentage of tolerance allowed for the difference between the colors and those websafe image. If the observation of the effects of keeping an eye on the "Color Table": the colors are changed, and as close as possible, when a similar tone, the 216 color palette websafe. Increasing the percentage of Block Web decreases the number of colors in the image.