Thresholding is moving the end points of the curve around to find the brightest highlight or darkest shadow. Please read the attached documents for a better explaination.
Greg
Thresholding
Good .PDF files on thresholding. I would like to make just one additional comment regarding what might perhaps be called "artistic" consideration.
In nearly all captured images, whether by scanner, film or digital sensor, the tonal range (light to dark) often extends beyond the range of the capture device. What this often means is that you should always ask yourself when establishing a threshold, what is the "significant" area here that needs to be used to set that threshold. In Greg's bee (nice shot!), the highlight threshold was the highlight reflection from the eye. In evaluating that as a threshold, I would expect nearly any reflection to be "blown out" and devoid of any detail. So no matter where we put the threshold for highlights, there will never be any detail in that reflection, so I would effectively ignore that when looking for some highlight area with detail. In other words, I might want to use another area to determine where to place the highlight slider.
Well, where? This is a very instructive image because there are only highlights, no areas of white detail, so, in effect there IS no "right" white point. The lightest area in which you really want good detail is in the light yellow of the bee's back, so I would consider using the highlight slider to creatively insure the best detail in this important area. In doing that, watch also that the reflected highlights that are not important do not "bloom" up in size.
On to the blacks. The artistic consideration there is to ask yourself how much shadow detail you want in the flower. Is it important to your vision of the image? Do you want the black slider to just barely bump the first black pixel (maximum shadow detail), or is another setting better for increasing contrast?
Clearly, there are no "right or wrong" ways to do this. Do spend a minute sitting on your hands and ask yourself how you want others to see your image before grabbing that mouse.
In nearly all captured images, whether by scanner, film or digital sensor, the tonal range (light to dark) often extends beyond the range of the capture device. What this often means is that you should always ask yourself when establishing a threshold, what is the "significant" area here that needs to be used to set that threshold. In Greg's bee (nice shot!), the highlight threshold was the highlight reflection from the eye. In evaluating that as a threshold, I would expect nearly any reflection to be "blown out" and devoid of any detail. So no matter where we put the threshold for highlights, there will never be any detail in that reflection, so I would effectively ignore that when looking for some highlight area with detail. In other words, I might want to use another area to determine where to place the highlight slider.
Well, where? This is a very instructive image because there are only highlights, no areas of white detail, so, in effect there IS no "right" white point. The lightest area in which you really want good detail is in the light yellow of the bee's back, so I would consider using the highlight slider to creatively insure the best detail in this important area. In doing that, watch also that the reflected highlights that are not important do not "bloom" up in size.
On to the blacks. The artistic consideration there is to ask yourself how much shadow detail you want in the flower. Is it important to your vision of the image? Do you want the black slider to just barely bump the first black pixel (maximum shadow detail), or is another setting better for increasing contrast?
Clearly, there are no "right or wrong" ways to do this. Do spend a minute sitting on your hands and ask yourself how you want others to see your image before grabbing that mouse.
Indeed that is the problem..when have you gone too far or not far enough?
I hate locked up shadows and blown out highlights. I always try to keep the specular highlights as the brightest points in the image unless there are none.
When shooting film, It was always a huge struggle to control the highlight / shadow exposure. The need to push or pull the process to try to save the details was always a consideration. With digital it gets easier but not completely fool proof. To me thresholding is the digital equivalent of push and pull processing both at the same time. You get to push the shadows and pull the highlights...How cool is that...
Greg
I hate locked up shadows and blown out highlights. I always try to keep the specular highlights as the brightest points in the image unless there are none.
When shooting film, It was always a huge struggle to control the highlight / shadow exposure. The need to push or pull the process to try to save the details was always a consideration. With digital it gets easier but not completely fool proof. To me thresholding is the digital equivalent of push and pull processing both at the same time. You get to push the shadows and pull the highlights...How cool is that...
Greg
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