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.
EscapeE features a number of parameters which you may configure to get the best image at the smallest file-size, see below.
You may choose to apply JPEG compression to images found in PDF, PDF/A, PostScript, IDF and HTML5 documents, while applying a different compression method to the rest of the document:
|1.||Select Configuration... from the 'Options' menu (f8) and choose PDF document as the 'Output' format.|
|2.||Select the Images tab then click the JPEG options... button.|
|3.||To apply JPEG compression to any JPEG images found in the document, tick if it was a JPEG. Alternatively,|
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:
|o||Always always use JPEG compression for all images (100)|
|o||Never never use JPEG compression for any image (0)|
|o||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.|
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.||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.|
|2.||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.
|3.||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.|
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.
More options for PDF export