This property defines how different types of images should be processed before being inserted into the PDF document. Each image type can be downsampled or converted, and the values and specifications are identical for all three types of images. The three image types are specified with the terms:
| • | Color |
| • | Indexed |
| • | MonoAndDrawings |
Valid directives would therefore be, for example:
| • | Graphics.Color.Downsample,1 |
| • | Graphics.MonoAndDrawings.Convert,2 |
Downsample
Downsampling refers to the process of taking a relatively high resolution file and reducing the amount of pixels used in that image. This works fine for a file that will be only viewed on a computer monitor or posted on the Web, but will significantly reduce the image quality of a file that will be digitally printed. For more precise control of file-space-saving techniques, see Compression.
Name |
Values |
Description |
|---|---|---|
Method |
0 (None) 1 (Linear) 2 (Bilinear) 3 (Bicubic) |
Specifies which method should be used for downsampling. If value is 0 (None), images of this type will not be downsampled. Default = 0 (None) |
To |
50-2399 |
These two properties define when an image should be downsampled. Default = 96 |
IfAbove |
51-2400 |
If the original DPI of the image is equal to or above that of the value specified by the property IfAbove, the image will be downsampled to the DPI specified by the property To. Default = 128 |
Convert
Name |
Values |
Description |
|---|---|---|
Method |
0 (None) 1 (ToGrayscale) 2 (ToMonochrome) 3 (ToBlackAndWhite) |
Specifies how images of this type should be converted. Value 0 (None) means that no images of this type will be converted. Default = 0 (None) |
Dither |
Boolean |
Specifies whether images should be dithered during conversion. This has meaning only for methods ToMonochrome andToBlackAndWhite. Default = True |
Examples
Downsampling a color image if over 100 dpi to 90 dpi. (On an actual test file consisting of a single 180 dpi image, this reduced the PDF file size from 1.3 MB to 27K)
//PDFX,Graphics.Color.Downsample.Method,Bilinear
//PDFX,Graphics.Color.Downsample.To,90
//PDFX,Graphics.Color.Downsample.IfAbove,100
Converting a color image to BlackAndWhite
//PDFX,Graphics.Color.Convert.Method,ToBlackAndWhite
//PDFX,Graphics.Color.Convert.Dither,true
Converting a color image to BlackAndWhite
//PDFX,Graphics.Color.Convert.Method,ToBlackAndWhite
//PDFX,Graphics.Color.Convert.Dither,true
Compatibility
In PDFXv3, "Downsample" and "Convert" were their own Properties, so the directives were, for example, "Downsample.Method,1" and "Convert.Dither,0."
