Upsample/downsample images
Sometimes it is required by a printer that all images in a PDF have at least a certain resolution. This can be difficult, especially if the low-res images are not available in a higher resolution, or the other way around.
pdfToolbox 13 has upgraded the handling of downsampling or upsampling images by adding some new methods to predefined Fixup Properties.
Downsample/compress images
- The available downsampling methods are:
- Average downsampling
- Subsampling
- Bicubic downsampling
- Lanczos downsampling
- BlackmanSinc downsampling
- "To": The target resolution
- "For images above": Images above the defined threshold would be excluded from downsampling
- Quality: Allows for specifying the quality level in which JPEG objects are saved after the conversion.
Note: The given value is interpreted as a percentage declaration between 0 and 100. Following you find the possible values and the equivalent setting in Adobe Photoshop:
Adobe photoshop values | JPEG quality compression |
---|---|
20 | Minimum |
40 | Low |
60 | Medium |
80 | High |
100 | Maximum |
Upsample/compress images
- The available upsampling methods are:
- Average upsampling
- Bicubic upsampling
- Lanczos upsampling
- BlackmanSinc upsampling
- "To": The target resolution
- "For images below": As it does not make much sense to upsample images with a very bad resolution, images below the defined threshold would be excluded from upsampling
- Quality: Allows for specifying the quality level in which JPEG objects are saved after the conversion.
Note: The given value is interpreted as a percentage declaration between 0 and 100. Following you find the possible values and the equivalent setting in Adobe Photoshop:
Adobe photoshop values |
JPEG quality compression |
---|---|
20 | Minimum |
40 | Low |
60 | Medium |
80 | High |
100 | Maximum |
More about the methods
When to use which method totally depends on the user. Here are some external links to:
- Lanczos resampling
- BlackmanSinc resampling: 'Blackman' window applied to a 'Sinc' filter for image resampling
- Bicubic resampling