The JPEG compression method was devised for storing real-world photographs as digital images. It reduces file-sizes considerably but information on color and luminance may be lost. Consequently, JPEG compression may not be the best choice for detailed images with sharp lines.
To configure 
EscapeE to get the best JPEG image at the smallest file-size, see Compression parameters below.
You may choose to apply JPEG compression to image(s) found in PDF, PDF/A, PostScript, IDF and HTML5 documents, while applying a different compression method to the rest of the document: see JPEG images in other documents below.
Experts may customize the values of the parameters used for applying JPEG compression to an image (see also command line option /JPEGOPTS). Note that this set-up is also used when exporting to PDF, PDF/A, PostScript and IDF.
| 1. | Choose Configuration... from the 'Options' menu (or press f8) to open the General page of the 'Configuration options' dialog. |
| 2. | Select JPEG images Output Format then click the Options... button alongside to show the JPEG Options page. |
| 3. | Tick the Low resolution color check-box to effectively average the color (rather than the luminance) of a number of pixels, yielding a smaller number of "bigger" color pixels. This results in smaller images with some loss of quality – sharp edges may appear fuzzy and colors smeared out, but this is usually acceptable for photographs. |
| 4. | Enter/select a value for image Quantisation quality:
100 for minimal degradation, but bigger files than
000 for heavily quantized (i.e. highly compressed but low quality) images.
Intermediate values may be used to vary the degree of quantization; the default value used is 50. |
| 5. | Tick the Coarse color quantisation check-box to allow the color to be rounded to fewer levels (fewer than the luminance values), again yielding smaller images with some loss of quality. This may be acceptable for graphic art using limited palettes. |
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| 1. | Choose Configuration... from the 'Options' menu (or press f8) to open the General page of the 'Configuration options' dialog. |
| 2. | Select PDF images Output Format then click the Options... button alongside to show the PDF Options page. |
| o | To apply JPEG compression to any JPEG images found in the document, tick if it was a JPEG. Alternatively, |
| o | set up a benchmark to determine whether JPEG compression is to be used or not. Enter/select a value for Use JPEG for images from the drop-down box: |
| • | Always always use JPEG compression for all images (100) |
| • | Never never use JPEG compression for any image (0) |
| • | If appropriate and set up an intermediate value to bias the set-up towards or against choosing JPEG compression; EscapeE defaults to using a value of 50. |
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Tip: you can check whether an image in the document on view was sourced from a file in JPEG format by looking for "JPEG" in the image's Graphic details.
Links
JPEG image file export
