After you have edited a collection of vacation pics or snapshots from a party, you may want to scale them for emailing. This doesn't seem like a big deal at first, but if you have to edit each image individually for an entire series of photos, this monotonous task can consume a huge amount of time. The remedy is basically ImageMagick [1], which batch-processes files, but can only be controlled using shell commands.

If you feel more comfortable with a graphical user interface, it is worth taking a look at Converseen [2], which is based on ImageMagick. For the install [3], you have a choice between an AppImage and Flatpak or Snap packages across various distributions. Some distributions also let you pick up Converseen via the package manager, and the source code [4] is available on GitHub if you prefer to build the tool yourself.

After setting up the program, launch by selecting the entry in the desktop menu, or type the converseen command in the shell.

The main window of the application is divided into two areas. On the right you see a (initially empty) list of all the images to be processed. You can add new files either via the File | Add images menu or by pressing the matching button in the toolbar. When you click on one of the entries, Converseen displays a preview in the sidebar on the left, along with information about the file type, file size, image size, and resolution (Figure 1). Checking an entry selects individual images to be edited, while Edit | Select all or the Check all button in the toolbar lets you select all entries.

Figure 1: The main window lists all the files you can edit. If you click on an entry, you will see a preview of the image on the left along with more detailed information about the file.

Processing PDF files

Converseen can do more than just edit image files. File | Import PDF File lets you read PDF documents and convert their individual pages into images. But for this to work, Ghostscript [5] must be available on the system, and you need to let ImageMagick access it.

In the current version 7 of ImageMagick, open the /etc/ImageMagick-7/policy.xml file with a text editor and comment out the policy directive for the delegate domain there, as shown in line 2 of Listing 1.

01 ### In /etc/ImageMagick-7/policy.xml:
02 <!-- <policy domain="delegate" rights="none" pattern="gs" /> -->
03 ### In /etc/ImageMagick-6/policy.xml:
04 <!-- <policy domain="coder" rights="none" pattern="PDF" /> -->
05 <policy domain="coder" rights="read|write" pattern="PDF" />

If you are still using ImageMagick 6, edit the /etc/ImageMagick-6/policy.xml file instead. As shown in line 4, you need to comment out the policy statement for the coder domain and replace it with the version from line 5.

Scale and Rotate

After selecting the desired images, turn to the Actions Panel on the left (Figure 2). Scroll down, and below the preview image you will see two tabs. Dimensions lets you scale the selected images.

Figure 2: You can use the Actions Panel on the left to configure the settings for the conversion.

To change the size, check Scale image. Use the selection field to decide whether you want to specify the size in absolute values (pixels) or as a relative value (percent). To keep the aspect ratio of the images, just check the box. Then enter the values to which you want to scale the images in the Width and Height fields.

You can adjust the value in Resolution. Save the values in DPI in the corresponding fields. (DPI stands for dots per inch – a unit of measurement for the resolution of image files. For the web, 72 DPI is usually fine, for print you will need 300 DPI.) If you want to rotate and flip images, switch to the tab of the same name. In Rotate image you can choose to rotate 90 or 180 degrees clockwise or counterclockwise. The field below lets you flip the images horizontally or vertically.

Output Options

In the lower part of the Actions Panel you can set the output options. First specify the filesystem location where you want Converseen to store the edited files.

By default, the program saves the images under their original names. If necessary, you can choose the file names yourself by selecting Rename. You can then add a prefix and a suffix to the name of the original file, which is represented by a hashtag (#). A name specification would look something like #_edited.

If you decide to use the Progressive number option instead, Converseen will number the processed files consecutively. It starts with the number you enter in the field below.