Zapisywanie obrazu w różnych formatach graficznych

• What are imageimageimage files used for?

• Does the file size affect the image quality?

• Does the purpose of an image influence the choice of its file formatfile formatfile format?

The criteria of selecting the image file format are based on:

• the quality and size of the imageimageimage intended for printing,

• the available space on a local disc or in a cloud,

• the speed of opening and saving the image,

• the purpose of the image (the image intended for placing on a web site).

A filename extension is a suffix to the name of a computer file following the last occurrence of the dot character that indicates a specific file type. Due to historical reasons (the DOS operating system) filename extensions usually consist of three characters. In Windows, filename extensions are used to assign file types to appropriate programmes that enable editing them.

A raster graphicsraster graphicsraster graphics is an image consisting of pixels arranged side by side, which form the grid of coloured points. Such images are also called bitmaps. They are usually created by devices such as a digital camera or scanner.

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Zrzut ekranu - Zapisywanie obrazu w programie Paint. Wybór typu pliku. Do wyboru mamy zaznaczony jako aktywny PNG (*.png) oraz Monochrome Bitmap (*.bmp; *.dib), 256 Color Bitmap (*.bmp; *.dib), 24-bit Bitmap (*.bmp; *.dib), JPEG (*.jpg, *.jpeg, *.jpe, *.jfif), GIF (*.gif), TIFF (*.tif, *.tiff).

BMP is a bitmaps supported by Windows. Their advantages are their simple structure and a common support by the Windows applications, while their disadvantage is the large file size. Bitmaps can support various colour palettes.

JPG is the most popular image file formatfile formatfile format using lossy compressionlossy compressionlossy compression, which can be characterised by the change of the colour value of particular pixels – this effect is not perceptible by human. It is used most of all for web images and by digital cameras. Its huge compression ratio can cause a significant reduction in the file size. Most applications are able to automatically adjust the compression to the visual quality of an imageimageimage.

PNG is a popular image file format supported by all web browsers. It is a non‑patented replacement for GIF. It supports lossless data compression and transparency. This file format is becoming more and more popular.

GIF is a file format supported by all web browsers that is the most suitable for storing images in a few colours. Its own colour palette is reduced to 256 colours, which may affect the quality of an image. GIF files can be animated.

TIFF is universally accepted as a standard of image files among the publishing industry. It enables using lossy and lossless compressionlossless compressionlossless compression. It is not suited to be used on web sites due to its large file size.

The size of raster imageimageimage files is positively correlated with the number of pixels in the image and the depth of colours (the number of bits per pixel). Compression is a method of reducing the number of bits needed to express a piece of information. Images can be compressed by using various methods. Lossy compressionlossy compressionLossy compression is a type of data compression that does not ensure that the reconstructed information will be identical to the original. Lossless compressionlossless compressionLossless compression is a type of data compression that allows the original data to be perfectly reconstructed from the compressed data.

When you select the image file format, you must take into account:

• its purpose (e.g. for placing on a web site, for printing etc.),

• its file size (the disc space taken up by the file),

• the quality you want to obtain.

The most popular image file formats are:

• BMP,

• JPG,

• GIF,

• TIFF.

Exercises

Glossary

Keywords

file formatfile formatfile format

imageimageimage

raster graphicsraster graphicsraster graphics