Posted by Peter Conway on July 30, 2009 at 2:17 AM
What is the full purpose and explanation of it?
Posted by Keith Bauer on July 30, 2009 at 11:32 AM
Hi Peter:
Here is the most common thing I do with the Threshold Layer.
- Add a Threshold Adjustment layer
- Move the slider to the right until you see most of the image completely black. The brightest part of the image will be in white. Chose the eyedropper tool, hold shift and click on one of the brightest parts of the image. This will place a "color sampler" at the brightest part. This will become the white point.
- Now move the slider to the left - Most of the image will be white at this point, with only the darkest part of the image in black. Again, using the eyedropper tool, hold shift and click on a black point.
- Now you can delete the Threshold adjustment layer.
- Using either Curves, or a Levels adjustment layer choose the white eyedropper and click on the "color sampler" point you set earlier for the white point. Then choose the black eyedropper and click on the "color sampler" point you set earlier for the black point. If these changes introduce a color shift (and it may), then change the blending mode on the Curves or Levels (depending on which you used) to Luminosity.
This technique can be used to help color correct and balance an image. It also helps to see what may print well or not from the brightest brights to the darkest darks.
If you have not already defined what values your black and white eyedroppers set you should do the following before the steps defined above.
Bring up a Curves Adjustment Layer. Double click on the black eyedropper tool. This will bring up the color picker tool. Set the "B" (Brightness) value to 5 percent and click OK. It will ask if you want to use this as the default. Choose yes. Do the same process for the white eyedropper tool except set it to 95%. Of course you can choose other values for your brightness or manually set values for R,G, B. The purpose of doing this is to set the values to something that can be printed. The default values before doing this are 0% for black and 100% for white. Those are not good values for most printing situations as the whites will definitely be blown, and the blacks and shadows close to black will be blocked up.
Posted by Lance Warley on July 30, 2009 at 12:17 PM
I use it the way Keith does.
Also,
- make the Info pallet visible so that you can see the RGB values for the points you create.
- I don't change to Lunminosity
- this works best with photos that have highlights and shadows.Otherwise, it can be too much..
Posted by Peter Conway on July 30, 2009 at 1:08 PM
Thanks, that makes sense. A related question (I think) is how do you determine if a part of an image is oversaturated? It may look good that way on screen but not print well. Is there an approach and rule of thumb about it?
...how do you determine if a part of an image is oversaturated? It may look good that way on screen but not print well. Is there an approach and rule of thumb about it?
Peter - There are two possibilities based on what you said.
1) It's so oversaturated that one of the color channels is clipped. You should be able to see this in the color histograms in the tool, or by other means, like the eyedropper (the value in that channel will be maxed out).
2) It not clipped, but is saturated beyond the gamut of the printer/ink/paper combo you're using. This is where soft-proofing shines. You can use a soft-proof to get an idea of what the print will look like, and look at gamut warnings, which will attempt to tell you when colors exceed what the ink/paper combo can reproduce. (There are other software packages for examining this kind of thing as well.)
Discussion
4 repliesHere is the most common thing I do with the Threshold Layer.
- Add a Threshold Adjustment layer
- Move the slider to the right until you see most of the image completely black. The brightest part of the image will be in white. Chose the eyedropper tool, hold shift and click on one of the brightest parts of the image. This will place a "color sampler" at the brightest part. This will become the white point.
- Now move the slider to the left - Most of the image will be white at this point, with only the darkest part of the image in black. Again, using the eyedropper tool, hold shift and click on a black point.
- Now you can delete the Threshold adjustment layer.
- Using either Curves, or a Levels adjustment layer choose the white eyedropper and click on the "color sampler" point you set earlier for the white point. Then choose the black eyedropper and click on the "color sampler" point you set earlier for the black point. If these changes introduce a color shift (and it may), then change the blending mode on the Curves or Levels (depending on which you used) to Luminosity.
This technique can be used to help color correct and balance an image. It also helps to see what may print well or not from the brightest brights to the darkest darks.
If you have not already defined what values your black and white eyedroppers set you should do the following before the steps defined above.
Bring up a Curves Adjustment Layer. Double click on the black eyedropper tool. This will bring up the color picker tool. Set the "B" (Brightness) value to 5 percent and click OK. It will ask if you want to use this as the default. Choose yes. Do the same process for the white eyedropper tool except set it to 95%. Of course you can choose other values for your brightness or manually set values for R,G, B. The purpose of doing this is to set the values to something that can be printed. The default values before doing this are 0% for black and 100% for white. Those are not good values for most printing situations as the whites will definitely be blown, and the blacks and shadows close to black will be blocked up.
Also,
- make the Info pallet visible so that you can see the RGB values for the points you create.
- I don't change to Lunminosity
- this works best with photos that have highlights and shadows.Otherwise, it can be too much..
Peter
Peter - There are two possibilities based on what you said.
1) It's so oversaturated that one of the color channels is clipped. You should be able to see this in the color histograms in the tool, or by other means, like the eyedropper (the value in that channel will be maxed out).
2) It not clipped, but is saturated beyond the gamut of the printer/ink/paper combo you're using. This is where soft-proofing shines. You can use a soft-proof to get an idea of what the print will look like, and look at gamut warnings, which will attempt to tell you when colors exceed what the ink/paper combo can reproduce. (There are other software packages for examining this kind of thing as well.)