Monkeybread Software - DynaPDF Manual

DynaPDF Manual - Page 542

Function Reference

Page 542 of 839

Quality comparison against JPEG

JPEG 2000 achieves in most cases a sligthly better result in comparison to JPEG for a given

compression ratio. Especially images with larger uniform colored areas achieve better results with

JPEG 2000 compression because this filter does not produce typical compression artifacts due to

color quantization which are typical for JPEG compression.

However, one thing that must be considered is the fact that Adobe's Acrobat uses another rendering

technique to display JPEG 2000 images. This leads to worse results because JPEG 2000 images are

rendered a bit blurry while JPEG images appear sharp. For a correct comparison render the file with

DynaPDF or compare images directly with an image viewer.

Embedded ICC profiles

JPEG 2000 images can contain an embedded ICC profile that can be used to create an ICC based

color space for the image (ICC based color spaces are device independent). To enable the usage of

embedded ICC profiles set the flag gfUseImageColorSpace with SetGStateFlags(). See also Color

Spaces and Images.

Pass-through mode

JPEG 2000 images can be inserted in pass-through mode. Pass-through mode is not enabled by

default since not all features are known which are unsupported in Adobe's Acrobat. To enable pass-

through mode set the flag gfRealPassThrough with SetGStateFlags().

Note that this flag just enables pass-through mode. That means the image is inserted in pass-

through mode if no scaling is required and if the image is probably compatible with Adobe's

Acrobat. Images in known incompatible formats are re-compressed as usual.

The output should be tested with Adobe's Acrobat or Reader when pass-through mode is enabled.

Why does DynaPDF not support LZW compression?

LZW is a very fast lossless compression filter that can be used for sampled images and arbitrary

binary data. Flate encoded output is usually more compact than LZW encoded output for the same

input, but Flate encoding is considerably slower than LZW. However, LZW encoding is marked as

obsolete by Adobe. Because it is not clear whether this filter will be supported in future versions of

Adobe's Acrobat, it will not be added to DynaPDF.

TIFF images

The TIFF image format is the most complex format of all available image formats. DynaPDF

supports a full featured implementation of the TIFF format incl. most currently available

compression methods and color spaces. TIFF images can be organized in scanlines, tiles or stripes,

all three formats are fully supported by DynaPDF.