Contents

# Compress

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).

若要使用此指令...

#### From the menu bar:

Choose Format - Image - Compress.

#### From the context menu:

Choose Compress.

#### From the tabbed interface:

On the Image tab, choose Compress.

On the Image menu of the Image tab, choose Compress.

#### From toolbars:

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

### Change 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.

相關主題

Wikipedia on image file formats.

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