Glenn ChanREELSony Vegas Tutorials

Linear Light Rescaling

The following images demonstrate rescaling done the typical way (on gamma-corrected components) and via linear light processing. In linear light processing, gamma correction is removed, then the image processing is applied, then the gamma correction is added back in. If rescaling is done in linear light, it is possible to (mostly) keep the # of photons of light emitted by the monitor the same. This maintains constant luminance- the image does not get darker.

In the zone plate test pattern below, the original image was scaled down 2X with the bilinear method and then scaled back up 2X using the nearest neighbour method. You can see that typical rescaling causes the image to become a lot darker compared to rescaling done in linear light. The middle image may appear lighter (or darker) compared to the original (left) due to monitor artifacts (CRTs especially have trouble showing zone plates with the correct luminance).

Original Linear light rescaling Typical (gamma corrected)

And the same images scaled 2X bigger by your web browser (this helps avoid the CRT artifacts; the upscaling is likely not linear light, so there may be subtle luminance shifts):

Original Linear light rescaling Typical (gamma corrected)

 

Source image: http://www.worldserver.com/turk/opensource/index.html

Now for some real world images... the following images were scaling down from a much larger original image.

In the book image below, the main difference occurs in the text in the middle. In my opinion, the typical image has text that's slightly easier to read. The linear light example looks slightly more natural. You can roll-over the images.

And 2X larger:

Image source: http://www.sxc.hu/photo/808156

In the bee image below, the main differences are the specular highlights on the bee's body and the water droplets on the leaves. There is also a difference in the specks of pollen on the bee's body. In my opinion, the specular highlights appear more natural with linear light rescaling.

And 2X larger:

Image source: http://www.sxc.hu/photo/789475



This site by Glenn Chan. Please email any comments or questions to glennchan /at/ gmail.com Eric Caton / Jemtec Boundary Noise Reduction reviews / comments versus Picturecode Noise Ninja, Imagenomic Noiseware, Topaz Denoise, Picture Cooler, Neat Image, etc.


My plugins:
Photoshop color correction
Photoshop noise reduction
Freeware

I wasn't satisfied with the tools in Adobe Photoshop so I made my own. Check them out!