/text/shared/01/image_compression.xhp image;compression image;reduce image size image;size reduction image;resize image;change resolution

Compress Image Compress the selected image to reduce its data size and resize the image in the document.

Image compression is a type of data compression applied to digital images, to reduce storage size or transmission time. Compression may take advantage of visual perception and the statistical properties of image data to preserve information quality. Image compression can be lossless or lossy. Lossless compression allows the original image to be perfectly reconstructed from the compressed data. In contrast, lossy compression permits reconstruction only of an approximation of the original image, therefore with some loss of quality, though usually with improved compression rates (and therefore reduced file sizes).

Select the image, choose Format - Image - Compress. Select the image, open the context menu and choose Compress.

Compression JPEG Quality Use the slider to adjust the level of quality of the JPEG compression, from 0 to 100. A value of 100 means no quality loss and a value of 0 may result in a very poor image. The default value of 90 produces very good results and significant image data size reduction. The compression values are not standardized between different JPEG image compression software. PNG Compression Since PNG compression is lossless, the main reason to use a compression factor less than 9 is when there is absolute need to reduce the size of the document when saving in a slow computer. The uncompress operation does not depend on the compression level. Resolution Reduce image resolution Check to change the dimensions of the compressed image. Width, Height Use the spin buttons to set the new width and height of the compressed image. Resolution Select the pixel density (dot per inch - DPI) of the image from the dropdown list. Interpolation Select the algorithm to calculate the interpolated pixels. Image Information Calculate New Size Click to calculate the size of the image data, based on the settings of the dialog box.

Wikipedia on image file formats.