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Eclipse Help Reference |
JPEG Files (*.jpg) |
The Joint Photography Expert Group (JPEG for short) is a group of representatives from companies and standardizing bodies that work together to create a standard for encoding images. Files that contain a JPEG encoding are referred to as JPEG files or JPEG File Interchange Format (JFIF) files. This encoding is designed to be a very compact format that uses lossy and lossless compression techniques in order to get high compression ratios while still having a similar appearance to the original image. It only has one parameter to control the degree of compression. It is called the “quality factor” and is a value from 1 (lowest) to 100 (highest). The chief benefits to this format is the resulting file sizes when compared to the uncompressed data, there is a JPEG viewer available on almost every computing platform and it is one of the common file formats used on the Internet.
JPEG images are usually not well suited to image processing due to the nature of the compression. For monochrome images, the lossy nature of the compression means that the brightness data is only going to approximate the image when viewed as a whole. There is no guarantee or upper bound on the error of any one pixel. The image is sliced up into tiny squares and then put back together on decompression. This gives the characteristic of a blocky look to over compressed images. It also confuses edge detection and processing functions since the edges of the blocks look like object edges.
For color images, the situation is worse. The color components are separated from the brightness of the image and the brightness is compressed as a monochrome image. The color components are then compressed even higher than the brightness since the human eye is less sensitive to this. When decompressed, the color is then added back in. Finally, resaving a JPEG image degrades the image even more since there is error introduced with every save.
We recommend that if you plan on using images in the JPEG format, that you also store them in an alternate format.
Eclipse supports the saving of JPEG images as individual files and as a sequential series. Depending on the complexity of your images, we recommend that you keep the Quality setting as high as possible. When saving a sequence, the current filename will be used (without extension) appended with a “#” and a number corresponding to the position in the sequence starting at 1 filled with zeros according to Decimals in Sequence and ending with a “.jpg” extension
Eclipse also supports the loading of JPEG images. This is done using the JPEG Drop in Loader. See Drop in Loader activation for more details. Once the Drop in loader is activated, it acts like a built in file format.
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