Monkeybread Software - DynaPDF Manual

DynaPDF Manual - Page 544

Function Reference

Page 544 of 839

Bitmap images

Bitmaps support alpha transparency but most image viewers discard the alpha channel. This can

lead to diffent results since DynaPDF considers the alpha channel in 32 bit bitmaps by default.

Since many 32 bit bitmaps contain an invalid alpha channel that is zero for all pixels, it is possible to

fully discard the alpha channel as most image viewers would do. This can be achieved by setting the

flag gfNoBitmapAlpha with SetGStateFlags().

GIF images

GIF images are LZW compressed images which are widely used in the internet. LZW is a loss-less

compression filter. Non-transparent GIF images are recompressed with the current compression

filter when inserting the image. The optimal compression filter for GIF images is Flate, and

therefore, the compression filter should be set to Flate before inserting such an image (see

SetCompressionFilter()).

Transparent GIF images are handled differently. GIF images use color key masking to achieve the

transparency effect. This kind of masking depends on exact color values and therefore, it is not

possible to compress such images with JPEG or JPEG 2000 compression without invalidating the

transparency information. To achieve correct results DynaPDF changes the compression filter for

transparent GIF images automatically to Flate and the image will not be downscaled independent of

the used settings.

Note also that transparent GIF images will be inserted transparent independent of the current

transparency settings. DynaPDF considers also the image resolution information if the image uses

different values for the x- and y-axis.

How to calculate the image size?

The calculation of the image size should be easy as possible. In most cases, images must be inserted

with exact proportions. Therefore, all image functions support two special values to make the

calculation easier. The width and height can be calculated as follows:

• If ScaleWidth or ScaleHeight is -1 the function uses the original width or height from the

image. If both parameters are -1 the image will be inserted with a resolution of 72 DPI.

• If ScaleWidth or ScaleHeight is 0, the missing value is calculated in relation to the given value

of ScaleHeight or ScaleWidth to preserve the image's aspect ratio. The resulting output is an

image with exact proportions relative to its original size.

• If ScaleWidth and ScaleHeight is 0, the original size is used (same effect as -1).

• A negative value of Width or Height mirrors the image on the x- and or y-axis.

Image Resolution

Images will be scaled to the defined resolution (see SetResolution()) if the original size is larger than

required, and if the property SaveNewImageFormat is set to true (default).