Another thing to note is that DOSBox only captures raw screenshots in their original resolution, so any screenshots or video captures you take will just be straight 320x200. If you want to get upscaled but properly aspect-corrected screenshots and videos, the best way to do it is to scale the captured image up to 1600x1200 using a simple point scaler which transforms each pixel in the original image into a block of 5x6 pixels in the new image. Depending on what software you use, the filter will labelled "point" or "none", or something similar. (If you do the math, you'll find that 1600x1200 is actually the smallest resolution that can give you a pixel-perfect representation of a 300x200, 4:3 image, because the pixels themselves have an aspect ratio of 5:6, and since 5 is prime, there's no region of square pixels smaller than 5x6 that can have exactly the same shape.)
In
GIMP, for example, you'd go to the "Scale Image" dialog, click on the little chain-link buttton in between the vertical and horizontal dimensions to stop it from maintaining the aspect ratio, choose "None" as the interpolation method, and then scale to 1600x1200. Then, if you want the image smaller, you can downscale it to a lower resolution, this time using one of the interpolative algorithms. You can also do all of this on the command line on either Linux or Windows with
ImageMagick: I like to use the "box" filter to downscale, so my command line is usually something like:
Code: Select all
convert input.png -filter point -resize 1600x1200! -filter box -resize 800x600 output.png
For videos, you can do a similar process with tools like
VirtualDub -- just set up a resize filter to scale to 1600x1200 without interpolation and with "maintain aspect" disabled, then add another subsequent filter to downscale to your desired resolution.
Here's an example of the Conquests of Camelot opening sequence that I prepared in this way using
AviSynth and
FFmpeg. (As an aside, I used the
ykhwong build of DOSBox to capture that video -- this has
Munt integrated into it, so the audio you're hearing is actually the game's MT-32 music.)
By the way, note that if you're embedding a screenshot into a web page, the best thing to do is actually to scale the image up to 1600x1200, as described above, and leave it at that resolution; specify the height and the width for the image to be displayed at in your HTML or CSS. This seems a bit counterintuitive, but the 1600x1200 image will actually have a smaller filesize than an image downscaled to a lower resolution with interpolation (every block of 5x6 pixels is a completely uniform region, so it's much more compressible), and the browser itself will downscale the image quite well, with the added benefit of simply downscaling it
less if the user zooms in on the page, and will still display a crisp and clear image with all of those wonderfully blocky pixels preserved. Compare these two images, for example:
original 1600x1200, and a
400x300 version downscaled with the box filter in ImageMagick -- the first file is actually smaller. (I'd embed them both here if this version of phpBB supported height and width parameters for the "img" tag.)
