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Reducing chromatic aberration

From: Photoshop CS3 Sharpening Images

Video: Reducing chromatic aberration

In this exercise we are going to begin the real world task of sharpening for source and specifically, we are going to be compensating for the anti-aliasing and interpolation that our function of the demosaicing process that I explained a few exercises back. We are also going to be adjusting for the softness that's a natural phenomenon under the photographic process, especially when we are converting the analog world into the digital realm of pixels and specifically, inside of this exercise, I am going to show you how to adjust for chromatic aberrations, which are misalignment of colors as a function of the light refracting through the lens element.

Reducing chromatic aberration

In this exercise we are going to begin the real world task of sharpening for source and specifically, we are going to be compensating for the anti-aliasing and interpolation that our function of the demosaicing process that I explained a few exercises back. We are also going to be adjusting for the softness that's a natural phenomenon under the photographic process, especially when we are converting the analog world into the digital realm of pixels and specifically, inside of this exercise, I am going to show you how to adjust for chromatic aberrations, which are misalignment of colors as a function of the light refracting through the lens element.

Now we are starting fresh here. I am looking at the Bridge and I have got the Bridge strained on this Festive ornaments.dng file inside of the 05_For_Source folder, which you will find inside the exercise files folder. I am going to go ahead and press Ctrl+R, or Command+R on the Mac in order to open that image inside of Camera RAW hosted by the Bridge. Now I could just go ahead and press Ctrl+Alt+0 or Command+ Option+0, which would zoom in on the center of the image, which happens to be me reflected on this silver ball. But that's not a very representative detail of this image.

I want something that shows off the best and the worst of the image. Now the focus happens to be locked more or less on this red ball down here in the lower left corner and bear in mind that I was working with an 18/ 135 millimeter lengths and I have got it zoomed all the way. So the focal length is a 135 millimeters. So this is quite the telephoto shot and I let auto-focus be in charge and the auto-focus happen to lock on best to this red ball down here at the bottom portion of the image and if I was to scroll up here you would see that this gold ornament that is poking out on us.

The mid-area of this image, the sort of mid-ring right there is in sharp focus. The point is in front, it's forward of the focal plane and the rest of the ornament is a little bit in back of the plane. But the portion in the image that I think is most representative, I will go ahead and zoom out here and scroll down by spacebar-dragging, the portion that I think is most representative is this gold ball right here with the texture and the reflections and so on. It's basically the best. As I say the best and the worst of all possible worlds where this image is concerned.

So I am going to go ahead and click a couple of times with my Zoom tool to zoom in and I will zoom in until I see that my zoom level down here in the lower left corner is 100%, which of course allows me to preview the sharpening settings. Now I will go over to this Detail tab right there or I could press Ctrl+Alt+3 or Command option 3 on the Mac and I am going to max out my Amount value. I am going to set it to its maximum which happens to be a 150%, which is lower than what you get inside Unsharp Mask and Smart Sharpen. They both allow you to go as high as 500%, bang in is the Amount value is much stronger here inside Camera RAW than it is inside Unsharp Mask or Smart Sharpen.

So 150% is more than a 150% inside of those dialog boxes. I am not going to tell you there is like a 150% equals 350% in the others because that is not actually true. It's a different algorithm. But it is a very strong amount. Now I am going to go ahead and max it out. The reason being, I want to be able to gauge what to set the other settings to. So setting the Amount value to it's maximum as a temporary measure, because obviously this is going too far, it's a great way to gauge the other settings. Now I am going to go ahead and zoom in on this highlight right there and I am going to zoom as far as I can, which is 400%.

Now as my magnifying glass gets empty at this point showing that I cannot go any farther. Known as these weird colors that are surrounding the highlight, they are actually, surrounding all of the highlights on this ball. They are most noticeable on this ball incidentally and we are seeing that we have a green edge along the right side of the highlight and a red, crimson, magenta edge over here on the left side of the highlight. This is a function of chromatic aberration. Now chromatic aberration is a function of the light refracting differently around the edges of the lens element than it does at the center of the lens element.

So all camera lens elements are calibrated so that the light refracts its absolute best right through the center of the lens element, but around the edges depending on your focal length, you are going to end up getting different sorts of chromatic aberrations to different degrees. So that's again another reason to crank up that amount value so you can see those chromatic aberrations. They contribute to dim focus inside of an image because we have a misregistration of detail and we can clear that up by going over here to the lens corrections functions.

So I'll go ahead and click on that tab or you can press Ctrl+Alt+6 or Command+Option+6 on the Mac. Here are two sliders that are available to us to fix the chromatic aberrations. We can either adjust the degree of Red/Cyan Fringe or we can adjust the degree of Blue/Yellow Fringe. Now in our case, its really neither of those. It is more like a red/green fringe, which makes me think we have got some cyan and yellow mixing up on one side and probably, some red and blue mixing up on the other side. Now what you do, notice that both values are zeroed out and zero means that the slider triangles are set right in the center.

No correction is being applied. In order to apply a correction you can drag this slider either way. I am going to take it over just for the sake of figuring out what I should be doing. I am going to take it over to the left and by the way, I should say that you do have to be zoomed in to a 100% or larger to see the effects of chromatic aberration. If I were to take this out, I am just going to zoom out until we get to 66.7% notice that any signs of what we are doing have disappeared from view. Even though there is no warning, we do have to be zoomed in to a 100% or better in order to see chromatic aberration.

Alright, so I am going to press Ctrl+plus a few times in a row, or Command+plus on the Mac until I am zoomed into a 400% once again. You can see that I am going in the wrong direction. Basically, I am making the problem much worse by dragging the slider triangle to the left. What does that mean? I need to drag it the right. Is basically what it comes down to and notice how it fixes the problem on the fly. So it is really great. You can really keep tabs on what is going on on screen here. I will take this value to something like 25%, lets say, which does seem to get rid of the colors we had before, that red-green scheme that we have before.

Now we have something of a violet-yellow scheme going on. So lets try adjusting the other slider and if we take it positive we make the problem worse as you can see. So lets take it negative instead. Notice those details as we move around. Basically, what Camera RAW is doing, it's a wonderful thing. Camera RAW is effectively rotating the color channels independently of each other and its doing it as it figures out what those colors should be. So its both manufacturing the channels and rotating them on the fly, very sophisticated technology at work here.

Now those values +25 and -10, just do wonders in order to get rid of this problem. Lets go ahead and turn off the Preview checkbox. So this is before and this is after. So obviously, we have done a great deal of good. There is still a little bit, if you look very closely there you can see that we still have a little bit of violet over here on the left hand edge and a little bit of weird saturation at any rate going on on the right hand edge of this highlight and I will show you how to fix that, very subtle, but it is fixable.

Now I will show you how to do that in the next exercise.

Show transcript

This video is part of

Image for Photoshop CS3 Sharpening Images
Photoshop CS3 Sharpening Images

115 video lessons · 17045 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 50m 30s
    1. Why every image needs sharpening
      2m 38s
    2. Understanding the effects of sharpening
      5m 26s
    3. Understanding the mechanics of sharpening
      4m 19s
    4. Understanding sharpening and gradual transitions
      3m 21s
    5. Understanding sharpening and noise reduction
      4m 0s
    6. Understanding amount and radius
      7m 50s
    7. Measuring your screen resolution
      6m 19s
    8. Using reliable zoom ratios
      5m 30s
    9. Calculating the actual print size
      4m 54s
    10. Gauging the ideal sharpening settings
      6m 13s
  2. 59m 31s
    1. Everyone knows you sharpen last (and everyone is wrong)
      1m 8s
    2. Understanding the conventional sharpening workflow
      5m 4s
    3. Flattening and saving to TIFF
      6m 39s
    4. Downsampling (and why you shouldn't upsample)
      6m 8s
    5. Understanding last-step sharpening
      6m 44s
    6. Recognizing problems with the conventional workflow
      9m 38s
    7. Erasing sharpening with the history brush
      4m 30s
    8. Using alternative sharpening workflows
      2m 37s
    9. Sharpening a scanned photograph shot on film
      2m 45s
    10. Sharpening a digital photograph
      3m 6s
    11. Sharpening specific details
      3m 43s
    12. Finding broad workflow conclusions
      2m 49s
    13. Learning that technique trumps timing
      4m 40s
  3. 1h 27m
    1. Comparing and contrasting neighboring pixels
      1m 6s
    2. Using the Gaussian Blur filter
      4m 25s
    3. Using Gaussian luminance distribution
      4m 47s
    4. Using the Unsharp Mask filter
      4m 54s
    5. Understanding the history of Unsharp Mask
      3m 51s
    6. Building your own USM with Gaussian Blur
      7m 35s
    7. Using the Smart Sharpen filter
      7m 35s
    8. Compensating for camera shake
      8m 50s
    9. Building your own Smart Sharpen with Lens Blur
      6m 59s
    10. Using directional sharpening with Emboss
      9m 13s
    11. Using Smart Sharpen extras
      8m 56s
    12. Using Convolution Kernels for more accuracy
      7m 8s
    13. Using the High Pass filter
      7m 32s
    14. Using Luminance Sharpening
      5m 5s
  4. 2h 14m
    1. Smoothing filters, smart objects, and masks
      1m 25s
    2. Using the Median filter and Dust and Scratches
      7m 7s
    3. Using Smart Blur and Surface Blur
      6m 12s
    4. Using the Despeckle filter
      8m 17s
    5. Softening flesh tones selectively
      10m 15s
    6. Using the Reduce Noise filter
      7m 27s
    7. Combining smoothing and sharpening
      8m 24s
    8. Making an image into a smart object
      9m 24s
    9. Applying editable smart filters
      6m 8s
    10. Combining two smart filters
      8m 5s
    11. Assigning a filter mask
      5m 59s
    12. Nesting one smart object inside another
      10m 32s
    13. Employing a static High Pass layer
      8m 59s
    14. Matching static pixel-level edits
      4m 37s
    15. Avoiding clipping with luminance blending
      9m 7s
    16. Sharpening and smoothing
      6m 36s
    17. Making an edge mask
      8m 14s
    18. Making a non-edge mask
      7m 17s
  5. 1h 33m
    1. Sharpening with Adobe Camera Raw
      1m 29s
    2. Introducing Camera Raw (4.1 or later)
      8m 13s
    3. Understanding why to sharpen for source
      5m 14s
    4. Using Camera Raw’s sharpening control
      5m 52s
    5. Previewing limitations and tricks
      6m 45s
    6. Why downsampling doesn’t work
      3m 12s
    7. Reducing chromatic aberration
      7m 30s
    8. Using the Defringe option
      3m 32s
    9. Understanding high frequency, low radius
      5m 21s
    10. Raising the Detail value
      3m 6s
    11. Using on-the-fly edge masking
      5m 41s
    12. Sharpening a low-frequency portrait
      6m 36s
    13. Eliminating color noise
      4m 47s
    14. Reducing luminance noise
      4m 42s
    15. Correcting “false sharpening”
      7m 15s
    16. Reducing shadow noise
      5m 22s
    17. Approximating ACR sharpening in Photoshop
      8m 35s
  6. 59m 8s
    1. Gauging and exploiting luminance frequency
      1m 27s
    2. Using low-frequency source sharpening
      5m 53s
    3. Using High Pass for portraits
      4m 19s
    4. Actioning a low-frequency edge mask
      7m 42s
    5. Modifying the source sharpening
      5m 21s
    6. Using high-frequency source sharpening
      5m 26s
    7. Using Smart Sharpen for cityscapes
      3m 2s
    8. Actioning a high-frequency edge mask
      5m 4s
    9. Downplaying color artifacts and clipping
      4m 4s
    10. Sharpening a medium-frequency image
      5m 24s
    11. Sharpening a layered composition
      7m 16s
    12. Sharpening for multiple frequencies
      4m 10s
  7. 1h 8m
    1. Who needs dull when you have sharp?
      56s
    2. Focusing in on a person’s eyes
      4m 22s
    3. Blurring the area outside the eyes
      4m 22s
    4. Sharpening eyes and other details
      5m 38s
    5. Darkening the lashes and eyebrows
      7m 13s
    6. Sharpening dark-haired people
      5m 2s
    7. Edge mask and emphasize
      3m 39s
    8. Nesting a Smart Sharpen effect
      4m 48s
    9. Density mask sharpening
      5m 35s
    10. Adding depth of field
      4m 39s
    11. Sharpening a background
      4m 23s
    12. Masking background from foreground
      8m 51s
    13. Eliminating halos around a person
      5m 38s
    14. Deepening and warming a background
      3m 28s
  8. 1h 18m
    1. Reverting back to convention
      1m 37s
    2. Understanding the use-neutral composition
      4m 15s
    3. Restoring much-needed antialiasing
      4m 2s
    4. Reducing noise in a high-frequency image
      7m 24s
    5. Making a third-level smart object
      3m 55s
    6. Preparing an image for print
      5m 18s
    7. Using ideal settings for commercial reproduction
      5m 37s
    8. Calculating very large-format settings
      5m 11s
    9. Using ideal settings for inkjet output
      4m 26s
    10. Sharpening for commercial reproduction
      5m 45s
    11. Sharpening for inkjet output
      4m 58s
    12. Revealing high-frequency multipass sharpening
      5m 21s
    13. Using Gaussian Blur to sharpen hair
      5m 41s
    14. Flatten, Save As, Resample, and Sharpen
      5m 9s
    15. Revealing low-frequency multipass sharpening
      3m 30s
    16. Sharpening an image for web or screen
      6m 22s
  9. 1m 50s
    1. Goodbye
      1m 50s

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