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increased color saturation solves hyper-contrast problems
EXCESSIVE CONTRAST PROBLEMS IN DIGITAL PHOTOGRAPHY CAN BE SOLVED VIA
PHOTO EDITORS IN COMPUTERS APPLYING INCREASED COLOR SATURATION AND THEN CORRECTION OF HUE, BETTER THAN THEY CAN BE SOLVED USING THE CONTRAST ADJUSTMENT CONTROLS IN SUCH PHOTO EDITORS. Sometimes in digital photography, you have the problem of getting exaggerated contrast in portraits. This problem is compounded by imperfections in the setting of white balance. Photos featuring excess contrast can be improved by increasing color saturation levels and then adjusting hue to compensate for the color changes produced by the changes in color saturation level. This approach can solve problems that you would not be able to solve using contrast adjustment controls that are specifically designed to adjust contrast. You can read plenty of attempts to describe what happens when the color saturation of a photograph is discussed on the internet. I present to you the simple truths it seems are too hard to find at these sites. A point of color in a digital image is determined by the luminosity of red, green, and blue at a point in the image. Various brightnesses of red green and blue combine to produce all the colors you see in digital images. The red green and blue levels for any point of color are measured from 0-255. When color saturation is increased, generally speaking, of these three color components in a color point, color components that are above the average luminosity of the three components in terms of luminosity, are increased in luminosity, while color components that are below the average luminosity of the color point are decreased in luminosity, with the rule being that the greater the divergence of the R G or B color element's luminosity from the average luminosity of the three R red G green and B blue elements in the color point, the greater the change in luminosity produced in the R G or B element in the color point by an increase in color saturation level. Increasing color saturation in an image, when two different colors are increased in saturation by an equal amount, can decrease the difference or contrast between the two colors, because the dominant brightest color (R red or G green or B blue) in the RGB spec of the two different colors is pushed to near the 255 maximum in both colors, as a result of which differences in luminosity of, for example, the R specs found in the different colors in the image decrease resulting in decreased contrast. When there is an increase in the luminosity of the dominant color in an RGB color point, if the color points vary from each other less in terms of the R G or B color element in the color point that increases in luminosity, than they do in terms of the R G or B elements in the color point that decrease in luminosity, as a result of the increase in color saturation, this can result in decreased contrast because the R G or B elements in the color points that contrast less from point to point in the image become more dominant, while the R G or B elements that contrast more from point to point become less dominant. Since the increase in color saturation pushes the (R G or B) colors in a color point that are relatively weak compared to other R G or B elements in the color point, in terms of luminosity, to even lower levels, this can result in a decrease in contrast when the major source of the excessive contrast is found in RGB elements in a color point that are relatively low in luminosity compared to the other RGB elements in the color point. You cannot just add up the differences in the numerical RGB specs in two different colors to determine how much those colors vary, because the sub-dominant colors (lower luminosity than the dominant color in the color point) in the rgb color points (points which are composed of red green and blue in various luminosities) have less impact on the color presented by the color point, the dimmer they are. There is less difference between RGB 255-70-0 and 255-0-0 than there is between 255-255-0 and 255-220-0; at lower levels of brightness in an RGB element in a color point, changes in the luminosity of the RGB element in the color point, change the color less than at higher levels of RGB element brightness. Thus it would appear that problems when a camera is exaggerating contrast, could be: the camera is producing excess differentiation from color point to color point in terms of the brightness of the brightest r or g or b component of the color point; the camera is not letting the most dominant components of the rgb points, which vary from point to point in the image less than other components of the rgb points, be bright enough compared to the other R G or B elements in the color point; and the camera is letting the subdominant elements of the RGB points in the photos, the colors that vary from each other more from point to point than the dominant R or G or B color in the color points, manifest themselves relatively speaking too brightly and impact the points of color excessively. Such hyper-contrast problems might be caused in part by incorrect white balance settings. Imperfect white balance setting, common when fluorescent tungsten and flash all combine to contribute to the lighting of a photo, can contribute to the problem of the exaggeration of the luminosity of for example the G or green element in RGB color points, resulting in contrast exaggeration which can be solved through color saturation enhancement such as I have been discussing. Incandescent and fluorescent white balance used in flash conditions, produce bluish tints; incandescent and flash white balance used in fluorescent conditions produce yellowish and greenish tints; and flash and fluorescent white balance used in tungsten conditions produces orangish (red combined with yellow which is a mix of red and green) tints. Thus fluorescent light photographed using flash white balance will produce yellow (a combo of red and green) and green tints; and tungsten light photographed using flash white balance will produce orangish (a combination of red and green) tints. So you can see how a camera overemphasizing the luminosity of the G or green elements in the RGB color points could lead to an exaggeration of contrast in flesh tones in which the R is most dominant, followed by the G Green and then the B blue; and you can see how such could be solved through increases in color saturation decreasing the relative luminosity of subdominant elements such as G Green elements in color points. When brightening light is shed on R red dominated faces, the brightening effect of the lights leads to an increase in the G green and B blue elements in the color points. You can see this from the way, if you take basic red, (R-255, B-0, G-0) pushing the B and G values higher and higher will make the color look brighter and whiter, make it look more and more like an overexposed photo or a photo subjected to excessive light. Thus you can see that light, which makes objects closer to white, and which is used to compensate for the limited light sensitivity of a camera compared to the eye, will tend to increase (in certain common R red dominated flesh color tones) the brightness of the sub-dominant G green and B blue elements to the point where they, mixing with the red elements of the color points, exaggerate contrast; and you can see how increasing color saturation, resulting in a decrease in the relative luminosity of the G and B elements in the color points, could reduce unwanted exaggeration in contrast. To reproduce what you see with the eye in limited light, you often have to, when using the camera, exaggerate the power of every light source you see with your eye in the natural light, while keeping the relative power of the various light sources compared to each other, the same as found in the natural scene. Thus, the camera is more sensitive to the blues and greens that dominate light from light sources (at least in terms of the effect of such light on color points that are R red dominated) than the human eye is. Therefore, after all is said and done, one can end up with portraiture that is unsatisfactory due to an excess of contrast, because it is the B blue and G greens in the RGB color points, that creat the excessive contrast, since the camera is compared to the human eye hypersensitive to them, and records them too emphatically or luminously or brightly; but one can recover from the problem by increasing the color saturation in the image so that the contrast producing G green and B blue elements are diminished in their ability to influence the colors produced by RGB color points. @2004 David Virgil Hobbs http://www.angelfire.com/ma/vincemoon |
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