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Capturing the differences between images

From: Photoshop CS6 One-on-One: Advanced

Video: Capturing the differences between images

In this movie, I am going to show you a terrific use for the Difference blend mode. Basically, it is the go to mode any time you are trying to find the differences between a couple of images, and that's because if a pixel on the active layer is the same color as the pixel behind it, then the composite pixel turns black, which means that anything that's not black is at difference. So let's say I am trying to create a screenshot of the Gradient Mesh feature inside Adobe Illustrator, and I went ahead and drew these two peppers, and now we're seeing the mesh points throughout.

Capturing the differences between images

In this movie, I am going to show you a terrific use for the Difference blend mode. Basically, it is the go to mode any time you are trying to find the differences between a couple of images, and that's because if a pixel on the active layer is the same color as the pixel behind it, then the composite pixel turns black, which means that anything that's not black is at difference. So let's say I am trying to create a screenshot of the Gradient Mesh feature inside Adobe Illustrator, and I went ahead and drew these two peppers, and now we're seeing the mesh points throughout.

And in my case, they are showing up as orange against a red background, which isn't a terrific amount of contrast. Now, I could have changed the color of those points in Illustrator, but I wanted still more control than that. What I wanted to be able to do was dim the peppers back, like you see them here, and then turn the points black, so that there is no ambiguity whatsoever, whether I show this image on screen, at my Web site, or whether I put it in one of my books, you can see those mesh points. So I'll go ahead and switch back to the image at hand.

Here's what we've got. I took one screenshot of the peppers with the mesh point selected, and I took another screenshot of the peppers deselected, and then I went ahead and set one on top of the other, and with the gradient mesh layer selected here, I'll go ahead and switch the blend mode from Normal to Difference, and we end up getting this effect here. So you can see everything that's not part of the mesh becomes black, and only the mesh lines remain. Now we need to turn all the differences white, so press Control+Shift+Alt+E, or Command+Shift+Option+E on the Mac, in order to merge the composite layers onto a new layer, and I'll call this new layer merged, and then you need to apply two adjustments.

You go up to the Image menu, choose Adjustments, and choose Desaturate, or if you loaded dekeKeys, you can press Control+Shift+Alt+U, or Command+Shift+ Option+U on the Mac, and that goes ahead and gets rid of all the color. And then you go up to the Image menu, choose Adjustments, and choose a command we haven't seen so far, Threshold, which allows you to turn all pixels on the active layer either black or white. And the reason this feature is called Threshold is because this slider triangle right there represents the threshold. If I take it down to, say, 110, then anything with a Luminance level of 110 or brighter becomes white; anything with a Luminance level of 110 or darker becomes black.

You can see we have got this tiny little histogram right there. We need to move the slider triangle all the way to the left of it. I ended up going with a Threshold level of 30, but I could have selected 20, for example, and gotten exactly the same results. As long as I'm inside of this area, it doesn't matter. All right. So I'll click OK. I've now got the white mesh point lines; everything that's not a mesh point is black. I want to convert that mesh to a selection, so I'll switch to the Channels panel, and press the Control key, or the Command key on the Mac, and click on RGB, and that goes ahead and selects anything that's white, and deselects anything that's black.

Now I'll switch to the Layers panel, turn off both merged, and grad mesh, so we are just seeing the no mesh versions of the peppers. I'll press Control+Shift+N, or Command+Shift+N on the Mac, to create a new layer. I'll call the layer mesh lines, and then I'll press the Enter key, or the Return key on the Mac, and I will press Alt+Backspace, or Option+ Delete on the Mac, to fill the selection with black. So we now have the black mesh lines. Go ahead and click outside the selection in order to deselect it, and now let's go ahead and give this no mesh layer a special treatment, so that it fades back, and I am going to do that using a layer effect.

So click on the fx icon, choose Color Overlay, and then click on the color swatch, and I recommend you change the Saturation to 0, and then change Brightness to 90. We need it to be bright, but something less than white. So 90% will work. Go ahead and click OK, and then switch the blend mode to Luminosity, so that we take out the luminance, but we leave the color behind, and then to bring back some of that luminance, I reduced the Opacity value to 70%, and then click OK.

And we end up achieving that effect that we saw at the outset of the movie in which the mesh lines are clearly distinguished from the artwork in the background. And that's one of the many ways to use the Difference blend mode in order to find the difference between two mostly identical images.

Show transcript

This video is part of

Image for Photoshop CS6 One-on-One: Advanced
Photoshop CS6 One-on-One: Advanced

124 video lessons · 18965 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 30m 4s
    1. Welcome to One-on-One
      2m 19s
    2. Loading the dekeKeys keyboard shortcuts
      6m 5s
    3. Remapping your Macintosh OS shortcuts
      3m 4s
    4. Adjusting a few general preferences
      4m 3s
    5. Using the visual HUD color picker
      2m 2s
    6. The interface and performance settings
      5m 31s
    7. Adjusting the color settings in Photoshop
      7m 0s
  2. 47m 0s
    1. Smart Objects
      1m 36s
    2. Three ways to place a Smart Object
      3m 6s
    3. Copying and pasting from Adobe Illustrator
      4m 11s
    4. Transforming and warping a vector object
      4m 48s
    5. Blending a Smart Object into a photograph
      3m 10s
    6. Blurring with a nested Smart Filter
      4m 57s
    7. Editing a Smart Object in Illustrator
      3m 20s
    8. Creating "true clones"
      3m 50s
    9. Duplicating a group of clones
      2m 53s
    10. Breaking the Smart Object link
      2m 53s
    11. Styling and blending Smart Objects
      2m 44s
    12. Editing originals; updating clones
      3m 41s
    13. Removing people from a scene with Median
      5m 51s
  3. 29m 59s
    1. Luminance meets sharpening
      1m 2s
    2. Correcting for lens distortion
      4m 39s
    3. Introducing Shadows/Highlights
      3m 54s
    4. Mitigating halos with Radius values
      4m 19s
    5. Enhancing the effects of Midtone Contrast
      3m 18s
    6. Creating a "bounce" with Gaussian Blur
      3m 29s
    7. Sharpening on top of blur
      2m 47s
    8. Masking a group of Smart Filters
      2m 53s
    9. Reducing the density of a layer mask
      3m 38s
  4. 49m 10s
    1. Using Curves
      2m 40s
    2. Introducing the Curves adjustment
      7m 36s
    3. Adding and editing points on a curve
      6m 27s
    4. Winning Curves tips and tricks
      8m 12s
    5. Correcting a challenging image
      6m 33s
    6. Selecting and darkening highlights
      4m 39s
    7. Neutralizing colors and smoothing transitions
      6m 6s
    8. The new automatic Curves function
      6m 57s
  5. 1h 31m
    1. Camera Raw
      2m 11s
    2. Opening and editing multiple images
      8m 1s
    3. Correcting white balance
      4m 8s
    4. The revamped Exposure controls
      8m 8s
    5. Working with archival images
      7m 54s
    6. The Spot Removal and Graduated Filter tools
      6m 4s
    7. Painting edits with the Adjustment Brush
      7m 23s
    8. Tone Curves (and why you don't need them)
      5m 57s
    9. Straighten, crop, and geometric distortions
      5m 17s
    10. Applying manual lens corrections
      5m 14s
    11. Vignette, chromatic aberration, and fringe
      6m 49s
    12. Selective hue, saturation, and luminance
      6m 36s
    13. Working with JPEG and TIFF images
      6m 36s
    14. Camera Raw Smart Objects
      6m 48s
    15. Editing Camera Raw images from Bridge
      4m 24s
  6. 32m 30s
    1. Duotones
      1m 23s
    2. Creating a professional-quality sepia tone
      4m 18s
    3. Introducing the Gradient Map adjustment
      5m 42s
    4. Loading a library of custom gradients
      3m 48s
    5. Creating a custom quadtone
      5m 48s
    6. Colorizing with blend modes and Opacity
      4m 6s
    7. Creating a faux-color, high-key effect
      7m 25s
  7. 1h 6m
    1. Noise vs. Details
      1m 28s
    2. Introducing the Reduce Noise filter
      7m 29s
    3. Correcting a noisy photo
      5m 33s
    4. Smoothing over high-contrast noise
      5m 50s
    5. Protecting details with an edge mask
      4m 52s
    6. Adjusting overly saturated shadows
      3m 35s
    7. Correcting with High Pass and Lens Blur
      3m 45s
    8. Brushing away blur and sharpening
      6m 42s
    9. Creating texture by adding noise
      5m 28s
    10. The Camera Raw Detail panel
      7m 8s
    11. Correcting noise and detail in Camera Raw
      8m 10s
    12. Adding noise grain and vignetting effects
      6m 47s
  8. 44m 30s
    1. Blur Gallery
      1m 36s
    2. Creating depth-of-field effects in post
      5m 29s
    3. Modifying your Field Blur settings
      4m 57s
    4. Editing and exporting a Field Blur mask
      6m 15s
    5. Adding a synthetic light bokeh
      3m 52s
    6. Using the Selection Bleed option
      7m 29s
    7. Creating a radial blur with Iris Blur
      6m 59s
    8. Creating "fake miniatures" with Tilt-Shift
      4m 35s
    9. Combining multiple Blur Gallery effects
      3m 18s
  9. 1h 34m
    1. Blend Modes
      1m 16s
    2. Using the Dissolve mode
      9m 47s
    3. Multiply and the darken modes
      8m 30s
    4. Screen and the lighten modes
      8m 10s
    5. Cleaning up and integrating a bad photo
      6m 38s
    6. Blending inside blend modes
      6m 55s
    7. Overlay and the contrast modes
      6m 53s
    8. A few great uses for the contrast modes
      9m 7s
    9. Difference, Exclusion, Subtract, and Divide
      5m 5s
    10. Capturing the differences between images
      4m 18s
    11. Hue, Saturation, Color, and Luminosity
      4m 45s
    12. Blend mode shortcuts
      6m 21s
    13. The Fill Opacity Eight
      8m 57s
    14. Using the luminance-exclusion slider bars
      8m 8s
  10. 44m 20s
    1. Color Range
      1m 14s
    2. Introducing the Color Range command
      7m 24s
    3. Selecting a complex image with Color Range
      5m 49s
    4. Refining a selection in the Quick Mask mode
      7m 4s
    5. Viewing a mask with or without its image
      4m 24s
    6. Painting directly inside an alpha channel
      5m 39s
    7. Correcting fringes around a masked layer
      8m 5s
    8. Turning a layer into a knockout
      4m 41s
  11. 59m 43s
    1. Refine Edges
      1m 28s
    2. Laying down a base layer mask
      6m 49s
    3. Introducing the Refine Edge/Mask command
      7m 57s
    4. Edge detection and Smart Radius
      4m 42s
    5. Using the Refine Radius tool
      7m 31s
    6. The transformative power of Refine Edge
      3m 37s
    7. Perfecting a mask with overlay painting
      10m 58s
    8. Combining Quick Selection with Refine Mask
      10m 37s
    9. Bolstering and integrating hair
      6m 4s
  12. 1h 18m
    1. The Pen tool
      1m 50s
    2. Pixel-based masking versus the Pen tool
      6m 45s
    3. Drawing a straight-sided path outline
      6m 57s
    4. Moving, deleting, and adding anchor points
      6m 10s
    5. Dragging control handles to modify curves
      5m 27s
    6. Converting a path outline to a vector mask
      5m 36s
    7. Customizing a geometric shape
      5m 53s
    8. How to position points and control handles
      7m 7s
    9. Drawing smooth points with the Pen tool
      8m 7s
    10. Duplicating and scaling a vector mask
      5m 21s
    11. Cusp points and the Rubber Band option
      6m 21s
    12. Setting anchor points in the pasteboard
      6m 8s
    13. Using the Convert Point tool
      6m 43s

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