DynaPDF Manual - Page 529

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Function Reference
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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 that that 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.
 

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