User:Van der Hoorn/Viking/Filters

Color images of the Viking landers can be generated by using the original .blu, .grn and .red images in the NASA Viking 1 image archive and NASA Viking 2 image archive. Those red, green and blue images don't have the same maximum wavelength as human vision has (see the table below) and thus the generated color images have a different coloring than we would consider 'true color'.[1]

Filter / Color	Peak wavelength of the Viking Landers	Peak wavelength of human vision	Modified peak wavelength of the Viking Landers
Red	700	650	0.7 * 700 + 0.3 * 550 = 655
Green	550	510	0.5 * 550 + 0.5 * 470 = 510
Blue	470	440	470

To generate images that are closer to our perception, we can use channel mixing. To create a more or less 'true color' image, do the following:

1. Download the .blu, .grn and .red PDS images from the NASA Viking image archive.
2. Convert those images to a format of your liking (e.g. jpeg, gif, png). You can use Nasaview to convert the PDS images to gif or jpeg.
3. Open the three images in Adobe Photoshop (or some other image editor of your liking).
4. In the channel view, use the 'Merge Channels..." function and select the RGB option. Then apply the correct image to the associated channel.
5. Use the Channel Mixer (Image > Adjustments > Channel Mixer...).
   1. Set the Red output channel to Red 70% and Green 30%.
   2. Set the Green output channel to Green 50% and Blue 50%.
   3. Leave the Blue output channel as it is (Blue 100%).
6. Now your image should have the peak wavelengths in the last column of the table above, which matches the peak wavelengths of human vision quite closely.