- Dimension = width and height in pixels.
- File Size = kB of disc space used by an image.
- Resolution = PPI (pixels per inch).
- Resize = Change print resolution without changing the number of pixels in an image. GIMP menu command is "Print Size"
- Resample = Change the number of pixels in an an image without changing the print resolution. GIMP menu command is "Scale Image"
When calculating the on-screen dimensions of an image, all that matters is the pixel dimension. Monitor resolution, in conjunction with the pixel width and height of the image, determines how big the image will appear on screen.
PPI (resolution) has no effect on the monitor display size of an images. Nor does it effect file storage size (on disc). PPI is simply a printing instruction.
Here are three views of Fairfax Courthouse from the SJW2 module map. All three images are 19kB and 200x200 pixels:
Resizing is changing the print size. This changes the PPI resolution without changing the number of pixels in the image. GIMP menu command is "Print Size"
Re-sampling is changing the pixel dimensions. GIMP menu command is "Scale image"
This changes the number of pixels in an image without changing the PPI print resolution.
Re-sampling changes width and height by reducing or increasing the number of pixels. There is no effect on PPI resolution. If you are re-sampling down, you are throwing away information from the file, which can’t be regained (so always work on a copy).
When re-sampling upwards (called interpolation) the graphics program creates pixels from nothing, so the result may appear fuzzy, which would necessitate a sharpening filter.
File size is controlled by compression which comes in large part from format used to save the image (VASSAL accepts png, jpg, and gif - the VASSAL designer's guide says that png is preferred).
Scanning for VASSAL
Scanners typically use the term "dpi" (dots per inch) instead of ppi.
Scan all game components at the same resolution. 100dpi is fine for VASSAL modules since we never expect to print these images, only use them on screen.
If after examining your 100 dpi scan, you need capture more detail, scan at 150 or 200dpi and then re-scale the image later. At 100 dpi your 32x22 inch map scan will have pixel dimensions of 3200x2200 (double that for 200 dpi).
- Scan black and white drawings in gray-scale mode.
- Save scans as either png or tiff - not as BMP files or GIFs.
- File format for final images: PNG is preferred, although the map may be saved as JPG if you are concerned about module size (megabytes).
- Don't use spaces in file names.