Many articles reference gamma-encoding in relation to the non-linear response of the human vision to luminance, insinuating or simply just stating that gamma-encoding has something to do with reconciling this with the linear nature of digital camera sensors. This is not true. We never see the gamma encoded image—the final image on our screens or in print is just what our camera recorded.
The confusion likely arises from the very similar exponential relationship between gamma-encoding approximately x 0. With that said, this similar relationship does have one significant benefit. By gamma encoding images using an exponent that very closely matches the human visual response to luminosity we can versus an unencoded, linear file reduce the bit depth of the image without a reduction in perceived image quality.
This is because human vision is more sensitive to changes in low light levels than it is to changes where light levels are high. By gamma-encoding data in such a way that matches our visual system, tonal values are more efficiently distributed and the threshold for posterization in terms of bit depth is lower.
Put another way, at higher luminosity levels we struggle to see the difference in a minor increase; whereas the same absolute change would be detected by us when light levels are low.
Also note how higher gamma values cause the red curve to bend downward. If you're having trouble following the above charts, don't despair!
It's a good idea to first have an understanding of how tonal curves impact image brightness and contrast. Otherwise you can just look at the portrait images for a qualitative understanding. How to interpret the charts. The first picture far left gets brightened substantially because the image gamma — is uncorrected by the display gamma — , resulting in an overall system gamma — that curves upward. In the second picture, the display gamma doesn't fully correct for the image file gamma, resulting in an overall system gamma that still curves upward a little and therefore still brightens the image slightly.
In the third picture, the display gamma exactly corrects the image gamma, resulting in an overall linear system gamma. Finally, in the fourth picture the display gamma over-compensates for the image gamma, resulting in an overall system gamma that curves downward thereby darkening the image. However, the effect of each is highly dependent on the type of display device.
CRT Monitors. Due to an odd bit of engineering luck, the native gamma of a CRT is 2. Values from a gamma-encoded file could therefore be sent straight to the screen and they would automatically be corrected and appear nearly OK.
This is usually already set by the manufacturer's default settings, but can also be set during monitor calibration. LCD Monitors. LCD monitors weren't so fortunate; ensuring an overall display gamma of 2. LCDs therefore require something called a look-up table LUT in order to ensure that input values are depicted using the intended display gamma amongst other things.
See the tutorial on monitor calibration: look-up tables for more on this topic. Technical Note: The display gamma can be a little confusing because this term is often used interchangeably with gamma correction, since it corrects for the file gamma. However, the values given for each are not always equivalent. Gamma correction is sometimes specified in terms of the encoding gamma that it aims to compensate for — not the actual gamma that is applied.
For example, the actual gamma applied with a "gamma correction of 1. A higher gamma correction value might therefore brighten the image the opposite of a higher display gamma.
Want to learn more? Discuss this and other articles in our digital photography forums. Exact matches only. Search in title. Search in content. Search in excerpt. Linearly Encoded. Gamma Encoded. Image File Gamma. The human eye perceives brightness according to the given scale. It looks correct to us since it is more consistent. The bottom scale displays the brightness levels as they actually are, e.
Gamma correction is basically mapping the physical brightness colors according to the top scale levels of brightness. Gamma correction in photo editing makes the picture look better. It helps us to adjust how a picture will be displayed on screen. If this is incorrect, the picture might either look too dark or washed out. It redistributes the tones in the picture to how we actually saw them. Gamma correction will keep the blacks and whites of the picture unaffected while affecting the mid-tones.
We measure the gamma value as an exponent. Photo editing softwares and apps keep the neutral gamma at 1. If we increase the gamma value by 2, it squares the brightness levels and if we decrease the value to 0.
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