The command line-based graphic software ImageMagick has proved suitable for the automatic generation of image versions in various resolutions and for format conversions. It is available for both Unix-based systems and for Windows and can be used without license costs.
You will find the commands for generating three different resolutions and a preview image in the JPEG format from an original scan in the TIF format as examples herein below. Moreover, you will find a command for the inclusion of a prepared footer and for the generation of the download versions in the PDF format.
convert original.tif -scale 1200 -quality 75 -strip standard.jpg
convert is the command for the generation of a converted and processed copy of the original image. All others are parameters defining this conversion more closely:
original.tif is the path and file name of the original scan. This file does not necessarily have to be available in the TIF format. If no path is specified (as in the example), ImageMagick expects the file in the current working directory.
scale 1200 establishes the width of the converted image at 1,200 pixels. You can, of course, also select another value between 1,000 and 1,500 pixels here. The proportion between height and width of the image is not changed by this manipulation.
quality 75 establishes the compression rate of the JPEG image. Values between 1 and 100 are possible here with higher values providing a higher image quality but also an increasing file size. Usually, a value between 75 and 85 constitutes a good choice.
strip removes all embedded metadata, such as colour ranges, from the file. This information is not required for the DFG Viewer and can be deleted with respect to a smaller file size.
standard.jpg establishes the path and the file name of the resulting image. In this process, the file extension determines the format. This file is submitted to the DFG Viewer later on.
convert original.tif -scale 700 -quality 75 -strip small.jpg
The width of the image is established at 700 pixels here. This corresponds to the smallest resolution in the Viewer (600 to 1,000 pixels), the provision of which is recommended.
convert original.tif -quality 75 -strip big.jpg
The image can be provided in its original size as the third zoom stage as an option. In this case, the scale parameter is missing since the resolution of the image is not to be changed.
convert original.tif -scale 150x150 -quality 75 -strip thumbnail.jpg
A version which does not exceed a size of 150 pixels in height and width is generated as an optional preview image. This is established via the parameter scale 150x150. The proportion between height and width is retained, however.
With the help of the ImageMagick command convert PDF versions of the individual pages can also be generated. These are then offered for downloading by the DFG Viewer.
convert standard.tif -strip -quality 75 standard.pdf
Since the target format is influenced by the file extension alone during the conversion, the command resembles the one for the conversion of the TIF file into the web-capable JPEG version (see above). Of course, the JPEG versions which have already been compressed and reduced in size can also be used as the source file in order to achieve smaller file sizes.
The tool pdftk, which is also available free of charge both for Windows and for Unix-based systems, is e.g. also suitable for compiling the PDF files of the individual pages to a PDF version of the total document afterwards.
pdftk standard*.pdf cat output book.pdf
pdftk starts the tool and the specification standard*.pdf submits the source files to the program. In this case too, the rule applies that the file is expected in the current working directory if there is no path specification. Moreover, the example is based on the assumption that individual pages were named on the basis of a comprehensible pattern, which already specifies the sequence of the pages – i.e. for example that such are numbered in an ascending sequence in the form standard001.pdf, standard002.pdf, etc. Otherwise, all pages have to be submitted expressly in the desired sequence as parameters here instead of using the wildcard character *.
cat specifies what is to be done with the source files. In this case, they are to be tacked together.
output in turn means that the result is to be output and that it is to be output in the form of the target file specified behind this - book.pdf. Since no path name is specified here either, the program will establish the file in the current working directory.
montage standard.jpg footer.jpg -tile 1x2 -geometry +0+0 -quality 75 standard.jpg
montage is the command for connecting several image files. As a precondition for that you need the pre-calculated version in the desired resolution (see above) and the footer to be included, which needs to have the same width.
standard.jpg and footer.jpg establish the path and the file names of the two graphics, which are to be connected.
tile 1x2 specifies the resolution of the resulting images in columns and lines. Since the footer is to be included below the digital representation, you select 1 column and 2 lines.
geometry +0+0 defines a possible offset of the two images from the upper/ left corner of the resulting graphic. Since both graphics are to be inserted in an aligned manner (i.e. without a frame), you select +0+0 here.
The information regarding quality (quality 75) should be selected in line with the parameter of the preceding convert command (see above).
The last specification designates the path and file name of the target file. In this case, the initial file is written over by the result of the calculation.
The German Research Foundation recommends the use of grey shades or black and white in the footer in order not to distort the overall impression of the digital representation with coloured accents. You can download <media 4420>prepared DFG logos</media> for use in your footers or you can use the DFG logo of the image archive of the DFG as an alternative.