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Reducing noise and correcting chromatic aberrations

From: Shooting and Processing High Dynamic Range Photographs (HDR)

Video: Reducing noise and correcting chromatic aberrations

Earlier I mentioned that it's not always possible to get to an absolute complete finished image in your HDR merging software, no matter what that software is. So while you can get your merge done, get your deghosting done, get your tone mapping the way that you want it, very often there are still things that will need to be done in your image editor. And in this chapter we are look at what those things might be, both correcting problems in an image and aesthetic changes to the image to finish it and complete it and make it into a nice final product.

Reducing noise and correcting chromatic aberrations

Earlier I mentioned that it's not always possible to get to an absolute complete finished image in your HDR merging software, no matter what that software is. So while you can get your merge done, get your deghosting done, get your tone mapping the way that you want it, very often there are still things that will need to be done in your image editor. And in this chapter we are look at what those things might be, both correcting problems in an image and aesthetic changes to the image to finish it and complete it and make it into a nice final product.

We are going to start in this movie by looking at noise reduction and the elimination of chromatic aberrations. So we are well in the realm of simple mechanical fixes. Just things that need to be done regardless of what your aesthetic is. You should have worked with these images earlier. These were the boys that had the ghosting problem. I have merged this image and deghosted it Photomatix, which we did in movie 05_11. If you didn't do that, go back and do it now and get all the way here to the tone mapping process. Then you can pick up with what I'm about to do.

I am going to zoom in here on his face, close to his face anyway. This magenta fringe here, this green fringe here, goes all the way around his ears. This is chromatic aberration. Normally it's an optical problem in your lens or an optical characteristic of your lens if you don't want to think that your lens has problems. It stems from a lens being unable to perfectly focus all wavelengths of light to the same point. If you would've looked at any of the individual frames that went into this HDR, you would not have seen this chromatic aberration.

Sometimes the merging and tone mapping process brings this out. So we are going to need to take care of that. We also, if you look up in the clouds, you see a noise problem, the speckle patterns here. Before we go on there is something that I am afraid I have to tell you about Photomatix. I probably should've mentioned it earlier but I will bring it up now. This preview that we are seeing here, this nice finished tone mapped image which is showing us the effects of our adjustments, it's not necessarily what our final image is going to look like.

To get this preview going in a reasonable amount of time the developers have to take some shortcuts. So there's a good chance that our brightness levels are going to be different when we finish. There's also a good chance that our noise levels are going to be different when we finish. So this is at best an approximation and that can be a little frustrating and it's another reason that we don't want to get a complete finished image here with Photomatix's controls, because we simply can't preview it in real time to see that finished image. So something you are going to learn to workaround.

Next step of course is to get my Tone Mapping settings set to where they should be, so I am going to fiddle with those a little bit and where I start with that is the way that I would start with any image editing. I am going to look at the histogram. I have a weak black point, I have no black point and very few dark tones, and that's why that has this washed-out look. That's highlight clipping. So I am going to go in here first right of the bat and just get my black point far more aggressive and that immediately puts some punch back in the image. I'm not going to play the black point like I would in a normal image edit because my preview is not actually I am going to leave myself a little head room.

So I want to be sure that I'm not getting anywhere close to clipping in case this image comes out darker than the expecting. So I am just ballparking the black point and saying that yeah I would like the contrast there. White point I've got some headroom here. I have got a little latitude. I could push the whites brighter. I don't want to overexpose anything and also it's a cloudy day. This image doesn't need to be too bright. So I am going to leave that there. So I usually start by just getting my tone ballparked so that I can simply see if I'm liking the image. If it's got the tonality that I think I want.

Now I can start working more on the HDR type effects. Remember the bulk of the HDR look is going to come from your Strength slider and your Smoothing controls. Remember too that you have got more smoothly and controls than just this smoothing slider. You have got this Micro-smoothing and these other controls down here. Micro-contrast is going to add more HDR crunchiness to it and Color Saturation is going to add that abed up HDR look, but Strengthen and Smoothing are really where the bulk of stuff happens. And a lot of times it helps to hit the extremes of these sliders just to figure out what kind of effect you are getting.

Now somewhere in here I think about what do I want? Do I want a real HDR look or do I want something that looks little more realistic? The sky is very dramatic, but I don't want it to upstage the kids here. So I am going to go for more of a realistic look than a really surreal HDR kind of look, so we are not seeing the whole image. There is not much else down here that I mean to worry about. It is just grass so I am going to leave that. So I am going to back off on the Strength a little bit and that's going to serve to calm the sky down a little bit and put the lighting back to be a little more realistic.

It should be brighter behind them because the sky though cloudy is still pretty bright. Now when I did that I lost a little bit of that black point correction that I had. The slider didn't move. It's just my blacks got shifted some. I am going to put back there, which brings the sky back a little bit into more of an HDR zone, then I am going to back off on that, so working at a balance of these. Let's take a look at smoothness. I am going to pull this all the way up here. I am going to look at all the way down here. Remember this is smoothing out the transitions between all of the tiny little bits of contrast change that have been made.

So I want to go for a more realistic look, which I feel like is more on this end of the spectrum, and the reason I'm saying that is again over here I'm seeing more brightness behind them, more shadows in front of them. Here I get more of a perfectly even flat exposure across the frame. This now looks like it's been artificially brightened. So I'm going to go back over here. Again with some images it's okay to have that fake processed look but these are three guys standing by the side of the road.

I want to keep that as realistic as possible. So I am going to put that somewhere in there. Just for curiosity I am going to turn on the other Smoothing mode and just see if I like any of these better. And this is pretty close to what I had manually so I am just going to stick with my dialed in smoothing controls. I want to just take a look at some of the Micro-smoothing and see if it makes any difference. Because this image doesn't have a lot of fine detail, I don't it's going to and it doesn't so I am going to leave that there.

Now I am looking at is going um, you know the contrast still isn't right, still looks a little washed-out. I am going to fix that in Photoshop. I don't know what the contrast really is so I am simply not going to worry about. Temperature, shooting in shade is always going to - if you are working with Auto White balance - leave a somewhat cool image I am going to try and warm this up just a little bit, not a lot, because it was cloudy, there wasn't a lot of color, but I do like the extra warmth. Saturation I'm not going to play that much with. Just to give you an idea what it would look like I can amp up the colors a lot and if I did that I would probably back off on the Temperature.

But again I'm not going for the hyperrealistic HDR thing so I am going to pull Saturation back and go with the warming that I had dialed in and I may play with saturation further. So I'm probably going to leave it there for now. I am going to zoom in here and show you that really bad noise problem in here that's going to have to be dealt with. Once I have got this the way that I think I want it, I hit the big old Process button that's sitting right over here. And that's going to sit there and actually do my tone mapping process and then it's going to show me the result. Don't panic when you see the result.

The reason I say that is the result looks soft. it doesn't really look like what I had before. So at this point I'm really not sure what I'm going to end up with. Let's get it into Photoshop and take a look for real. I'm going to save this back into the folder for the source images were and what Photomatix has done is kept my original name and had it tone mapped at the end. I am just going to save this out as a 16 -bit tiff file. I want 16 bits because that's going to give me a lot of editability and once that's done I am going to go open the image in Photoshop.

So now in my folder where the original image is, here's my tone mapped version. If I wanted I could just grab all of these together and stack them. So now I have my tone mapped HDR with all of its original source files sitting underneath it. Open this up in Photoshop. In Bridge I can do that just by double-clicking. Now let's take a look at what we got. And it came out a little warmer than I thought. It's kind of yellow but I am going to worry about that. It still looks soft. But when I zoom in I find that actually I have got pretty good detail.

The noise isn't a great. There's still some noise in here. Chromatic Aberrations are a drag so let's hit those first. I can fix Chromatic Aberrations on any type of image. All of the edits that we are looking at here are not things that you do only to HDR. This point we are out of the HDR processing realm. We are just doing normal Photoshop stuff. Anything you're seeing here you could do to any type of image. Filter > Lens Correction. Chromatic Aberration is normally a lens artifact, so it gets addressed in Lens Correction filter.

Auto Correction. I don't want any auto correction stuff going on. I am going to turn this off. I will go over here to the Custom control. Now to fix Chromatic Aberration I need to be able to see it so I am going to zoom in here to 100% and take a look at these fringy things here. Chromatic Aberration sliders over here. Fix Red/Cyan Fringe, Fix Green/Magenta Fringe, Fix Blue/Yellow Fringe, I have a green/magenta fringe. I want less of it so I am going to dial this down. Now you may think would you ever want more and dial it up? No but there are some times where the fix works by sliding the slider to other direction don't worry about understanding it, just try moving the sliders in either direction.

What Photoshop is doing here is moving individual color channels around so that they fall back in to registration. It's doing it in a very intelligent way now. Sometimes when I fix Chromatic Aberration here I might be introducing it over on one of the edges of the image. Look over here on the edge. I am not worried about this because it's outside the photo. You can see that I picked up a bunch of red fringe. That's because the red that was hanging our off of his left side has been shoved to the right. And it's fallen out the other side of the image in a way.

So I am looking pretty good here. That's taken care of the chromatic aberration problem. I am going to hit OK. Let's think about noise. Bad noise down here, some color noise in the skin tones, and a little bit of noise up in the sky. Nothing that bad. Thing to remember about noise is you shouldn't worry too much about it until you see your final output. If your final output is 640x480 image we are posting on the web go ahead and make that image and see how bad the noise is.

This is a 21 megapixel image. These individual pixels are very, very, very small when print it so that may not be an issue, but this is pretty bad noise I want to take a look at. I am going to go to Filter > Noise > Reduce Noise and that's going to pop up this Noise Reduction dialog box and wow! It's done a pretty good job already. This preview can be panned about and zoomed and if I click and hold the mouse button I see the original image, so that's my original noisy image. I am going to let go of the mouse button and there's my corrected version and I got to tell you, I don't think this needs much more.

These controls over here, the Strength of the Noise Reduction, how much to preserve detail. Noise Reduction works by going in and applying a lot of very selective blurs. So you're always possibly sacrificing detail for the sake of less noise. So that's why these are grouped together. We want to balance them. That means we want to apply only as much Noise Reduction as we have to, because that will potentially help preserve our details. So I am going to dial this down a little bit and see if it still works and it looks like it does.

So let's not add any stronger noise reduction then we have to, but maybe we need to go back up a little bit. Yeah, let's clean that up a little bit more. There are two kinds of noise. There are these simple speckle patterns that are luminance noise and then there are the colored splotchy patterns that are color noise. So we have separate controls for those and the defaults are really doing good job. I am going to leave the sharpen details where they are at because I think this is looking very good. Hit OK, let it process the image, which it should do pretty quickly.

And I've taken care of and chromatic aberration and my noise. This image needs a lot more work. Right now we're just looking at just the noise and the chromatic aberration. Because of the chromatic aberration adjustment, my image is no longer perfectly squared to its original canvas size. If I go up here to the top you can see that I picked up some transparent pixels. At some point I want to crop that out. So save this image, I am just going to do a normal save because this was already a tiff file and if you are wondering where that Layer box came from, when I did the chromatic aberration fix it floated my background layer.

So it's no big deal. Save that image and now back here in the Bridge my tone mapped tiff file now updates to show the corrected noise and chromatic aberration trouble. This image needs some more work but at least we fixed those crucial purely technical mechanical details.

Show transcript

This video is part of

Image for Shooting and Processing High Dynamic Range Photographs (HDR)
 
Expand all | Collapse all
  1. 6m 46s
    1. Welcome
      2m 0s
    2. What you need for this course
      2m 37s
    3. Using the exercise files
      2m 9s
  2. 24m 55s
    1. Dynamic range defined
      4m 31s
    2. Understanding bit depth
      3m 37s
    3. Image sensor and shadows
      2m 38s
    4. Three methods for capturing more dynamic range
      3m 56s
    5. HDR shooting and processing
      4m 40s
    6. Single-shot HDR
      2m 43s
    7. When to use HDR
      2m 50s
  3. 19m 59s
    1. Finding HDR subject matter
      4m 38s
    2. Shooting HDR
      9m 45s
    3. Workflow and organization
      5m 36s
  4. 17m 52s
    1. Using gradient masks to improve dynamic range
      3m 56s
    2. More dynamic range masking
      8m 57s
    3. Masking with brushes
      4m 59s
  5. 1h 35m
    1. Creating an HDR image in Photoshop
      12m 15s
    2. Creating an HDR image in Photomatix
      22m 5s
    3. Creating an HDR in HDR Efex
      11m 47s
    4. Merging in Photoshop and processing elsewhere
      3m 51s
    5. Using Tone Compressor in Photomatix
      4m 25s
    6. Using Exposure Fusion in Photomatix
      7m 35s
    7. Single-shot HDR images in Photomatix
      4m 18s
    8. Single-shot HDR images in HDR Efex
      1m 3s
    9. Single-shot HDR images in Photoshop
      5m 32s
    10. Ghosting and Photoshop
      2m 51s
    11. Ghosting and HDR Efex
      2m 47s
    12. Ghosting and Photomatix
      6m 36s
    13. Batch processing in Photomatix
      10m 51s
  6. 2h 9m
    1. Reducing noise and correcting chromatic aberrations
      13m 33s
    2. Finishing an image
      8m 42s
    3. Handling HDR images that are "flat"
      13m 37s
    4. Combining HDR and LDR
      19m 40s
    5. Selective editing with HDR Efex Pro
      9m 42s
    6. HDR that doesn't look like HDR
      12m 42s
    7. Tone mapping troubles to watch for
      6m 46s
    8. Why use HDR for black-and-white images?
      5m 26s
    9. Black-and-white HDR
      12m 39s
    10. Panoramic HDR
      12m 3s
    11. HDR time lapse
      4m 24s
    12. Processing the trestle image
      10m 1s
  7. 37s
    1. Goodbye
      37s

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