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09/04/2007 03:14:00 PM · #1 |
Many times after processing a picture in Photoshop I end up with a histogram that looks like this:
Is that bad even if the photo looks great?
Or sometimes it's clipped even more so I just go to curves and move the black and white point so it's not pure black and white and I end up with something like this:
Is that bad?
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09/04/2007 03:17:07 PM · #2 |
Originally posted by maggieddd:
Is that bad even if the photo looks great? |
Goal is making a great looking photo, not a great looking histogram. If the pic looks good then I'd say you met the goal. |
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09/04/2007 04:35:03 PM · #3 |
But if you have a great looking image, you will also have a great looking histogram to match. ;D
It depends on the picture. If you are shooting high key, you are going to have a lot of image data on the right. If you are shooting low key, you are going to have a lot of image data on the left. If you have a nice even lit subject, then you are going for a even spread of data on both the right and left side. The hump part (vertical lines) doesn't really matter to much as that is showing how much of that tonal range is there. The histogram is a great tool to know how to use, but you have to consider the image you are trying to achieve as well.
Mike
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09/04/2007 05:01:29 PM · #4 |
| Remember that the histogram is a tool for making great photos ... and the photo is not a tool to make a great histogram. Great photos are not necessarily the result of a perfect sinewave histogram. There is no such thing as a perfect histogram ... but there are such things as bad histograms that do result in poor photos. I normally don't even use a histogram ... make the pic look good like you intended and then if you want check it to see if and how much clipping you may have had. |
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09/04/2007 06:11:23 PM · #5 |
Your first histogram shows that you've clipped a little bit at both the black & white ends. Whether that's OK or not depends entirely on your intent. If you wanted to retain subtle detail in the areas that are clipped, it's bad. If you do want some pure blacks & pure whites in the photo, it's just fine.
Your second histogram is not good. It's almost never good to reduce contrast on an image that's already been clipped. All you do is compress the remaining data into a narrower range. In your example, there will be pixels that were clipped to white, but after the compression will all be a shade of gray that is just off white. Blacks will all be a dark gray rather than pure black. This is almost always undesirable.
BTW, you might want to consider turning on the RGB histogram if you are using CS or above. That will show you clipping for each channel individually, which is more accurate than looking at luminosity only. |
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09/05/2007 10:27:46 AM · #6 |
thanks for the comments.
I do understand that my whites and blacks are clipped. This is a common occurance after all my processing is done. I am trying to learn how to avoid that.
I am confused by the RGB histogram. If it shows me that my blues are clipped, what does that mean? What do I do about it? Desturate blues? I put RGB histogram on my Canon 5D for a while but that also was confused me because the histogram would not show anything clipped but the display would have blinking spots showing me overexposed areas. |
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09/06/2007 03:50:54 PM · #7 |
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09/06/2007 04:21:54 PM · #8 |
Depends on the photo. Is this pretty much straight out of the camera or did you already edit it in photoshop? The heavier editing you do the more data you will lose. If it looks good to you then do nothing assuming of course what you see on your monitor is what prints out.
Message edited by author 2007-09-06 16:24:45.
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09/06/2007 05:14:32 PM · #9 |
Originally posted by yanko:
Depends on the photo. Is this pretty much straight out of the camera or did you already edit it in photoshop? The heavier editing you do the more data you will lose. If it looks good to you then do nothing assuming of course what you see on your monitor is what prints out. |
this is after processing. I shoot in RAW so when I convert from RAW I end up with a histogram which is "ideal" nothing is clipped, but after processing I get what you saw on my first histogram (or sometimes worse).
I am wondering if I would be better off converting from RAW leaving some space on both sides of the histogram to have some room for processing in Photoshop?
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09/06/2007 05:41:36 PM · #10 |
| I am following this thread with interest as this is a topic that I have wondered about but never got around to discussing. |
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09/06/2007 06:33:00 PM · #11 |
Originally posted by maggieddd:
I am confused by the RGB histogram. If it shows me that my blues are clipped, what does that mean? What do I do about it? Desturate blues? I put RGB histogram on my Canon 5D for a while but that also was confused me because the histogram would not show anything clipped but the display would have blinking spots showing me overexposed areas. |
The blinking areas are areas where total luminosity is clipped. In theory, you can't have clipped areas in luminosity unless all of the RGB channels are clipped. If we think about it, this means we can have two clipped channels and still have no clipping in luminosity! This is why the luminosity histogram on the camera lies, and not in a good direction.
In determining luminosity, Green is weighted heaviest (0.59) followed by Red (0.30) and finally Blue (0.11). The calculation for luminosity is:
R*0.30+G*0.59+B*0.11
Given this, it's easy to clip Blue and/or Red and not detect it in luminosity. It's harder to do so with Green, but still possible. This is what's happening to you.
In order to avoid single-channel clipping, set the in-camera histogram to display the RGB histogram, and watch it carefully. Realize that you do have some ability to recover a blown channel, so don't be put off by a little clipping on one channel. In RAW conversion, if you're using CS3 or Lightroom, use the "Recover" slider to bring the errant channel back into line.
Now, in post-processing, there are several processes that can drive areas into clipping, in particular:
- USM, especially large-radius USM used for local contrast enhancement
- Brightness/Contrast adjustments, or most other contrast-related adjustments, except: curves with the endpoints left at the corners
- Color balance or Hue/Saturation adjustments where the saturation of one or more colors is increased
Watch your histogram when performing these (and other) adjustments. If you are editing in a 16-bit per channel space, it's not a bad idea to leave a small amount of "space" at the ends of the histogram if you know you'll be applying contrast-related adjustments or boosting saturation. Final tweaks to black and white points can be made late in the game. I wouldn't recommend this strategy when editing in 8-bit mode, however, since the number of available levels is already small.
Message edited by author 2007-09-06 18:33:26. |
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09/07/2007 11:52:48 AM · #12 |
Originally posted by kirbic:
Originally posted by maggieddd:
I am confused by the RGB histogram. If it shows me that my blues are clipped, what does that mean? What do I do about it? Desturate blues? I put RGB histogram on my Canon 5D for a while but that also was confused me because the histogram would not show anything clipped but the display would have blinking spots showing me overexposed areas. |
The blinking areas are areas where total luminosity is clipped. In theory, you can't have clipped areas in luminosity unless all of the RGB channels are clipped. If we think about it, this means we can have two clipped channels and still have no clipping in luminosity! This is why the luminosity histogram on the camera lies, and not in a good direction.
In determining luminosity, Green is weighted heaviest (0.59) followed by Red (0.30) and finally Blue (0.11). The calculation for luminosity is:
R*0.30+G*0.59+B*0.11
Given this, it's easy to clip Blue and/or Red and not detect it in luminosity. It's harder to do so with Green, but still possible. This is what's happening to you.
In order to avoid single-channel clipping, set the in-camera histogram to display the RGB histogram, and watch it carefully. Realize that you do have some ability to recover a blown channel, so don't be put off by a little clipping on one channel. In RAW conversion, if you're using CS3 or Lightroom, use the "Recover" slider to bring the errant channel back into line.
Now, in post-processing, there are several processes that can drive areas into clipping, in particular:
- USM, especially large-radius USM used for local contrast enhancement
- Brightness/Contrast adjustments, or most other contrast-related adjustments, except: curves with the endpoints left at the corners
- Color balance or Hue/Saturation adjustments where the saturation of one or more colors is increased
Watch your histogram when performing these (and other) adjustments. If you are editing in a 16-bit per channel space, it's not a bad idea to leave a small amount of "space" at the ends of the histogram if you know you'll be applying contrast-related adjustments or boosting saturation. Final tweaks to black and white points can be made late in the game. I wouldn't recommend this strategy when editing in 8-bit mode, however, since the number of available levels is already small. |
Thank you very much.
So I tried a little experiment. I converted my RAW image but I left it looking flat, leaving space to the left and to the right of the histogram.
I did all my adjustments and the picture still gets clipped. It happens when I add saturation. And even if it is just a little of it. I am wondering how to create a "velvia" looking image without clipping channels. It seems impossible. Any ideas? |
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