4.4. Compressing Images
| 4. Common Tasks |

### 4.4. Compressing Images

그림 3.21. JPEG 으로 저장하기의 예제 이미지

If you have images that take up a large space on disk, you can reduce that space even without changing the image dimensions. The best image compression is achieved by using the JPG format, but even if the image is already in this format, you can usually still make it take up less space, as the JPG format has an adaptive compression scheme that allows saving in varying levels of compression. The trade-off is that the less space an image takes, the more detail from the original image you lose. You should also be aware that repeated saving in the JPG format causes more and more image degradation.

To save you image as a JPG file, therefore, use File → Save As to open the “Save As” dialog.

그림 3.22. “Save As” Dialog

The dialog opens with the file name already typed in the Name box. If the image is not a JPG image, delete the existing extension and type JPG instead, and GIMP will determine the file type from the file extension. Use the file extension list, circled in the figure above, to see the types supported by GIMP. The supported extensions change depending on your installed libraries. If GIMP complains, or if “JPEG” is grayed out in the Extensions menu, cancel out of everything and step through the 4.7절. “모드 변경하기”. Once you have done this, click Save. This opens the “Save as" ” JPEG dialog that contains the quality control.

The “Save as JPEG” dialog uses default values that reduce size while retaining good visual quality; this is the safest and quickest thing to do.

그림 3.23. “Save as JPEG” dialog with poor quality.

Reduce the image Quality to make the image even smaller. Reduced quality degrades the image, so be certain to check “Show preview in image window” to visually gauge the degradation. As shown in the figure above, a Quality setting of 10 produces a very poor quality image that uses very little disk space. The figure below shows a more reasonable image. A quality of 75 produces a reasonable image using much less disk space, which will, in turn, load much faster on a web page. Although the image is somewhat degraded, it is acceptable for the intended purpose.

그림 3.24. JPEG 으로 이미지 저장하기 대화 상자

Finally, here is a comparison of the same picture with varying degrees of compression:

그림 3.25. 높은 수준의 JPEG 압축의 예제

Quality: 10; Size: 3.4 KiloBytes

Quality: 40; Size: 9.3 KiloBytes

그림 3.26. 적절한 수준의 JPEG 압축의 예제

Quality: 70; Size: 15.2 KiloBytes

Quality: 100; Size: 72.6 KiloBytes

4.3. Change the Size of an Image for print |  | 4.5. 이미지 잘라내기