Content Aware Scaling in Photoshop CS6

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In Photoshop CS6, content-aware scaling (also known as seam carving) is a cool image-sizing feature.

Advantage

  • Resize and reshape your images without the distortion of the content and composition.
  • Preserves image quality much better than traditional transformations.

Here’s how to apply content-aware scaling:

  1. Choose your desired layer in the Layers panel. If you want to isolate the scaling to a selection on the layer, make that selection now.

    Content-aware scaling doesn’t work on adjustment layers, layer masks, individual channels or Smart Objects. If you’re scaling a Background layer, choose Select→All.

  2. Choose Edit→Content-Aware Scale.
  3. Specify your options on the Options bar as follows:
    • Reference Point: Click a square in the reference point box to specify the axis point. The default location is the center.
    • Use Relative Positioning for Reference Point (triangle icon): Select this option to specify the new axis point in relation to its current position.
    • Amount: This option specifies the ratio of content-aware scaling to normal scaling. To minimize distortion, specify your Threshold amount. Start with a higher percentage and then adjust accordingly, if necessary.
    • Protect: You can designate areas that you want to protect from scaling by selecting them and saving them as alpha channels. If you have an alpha channel, choose it from this submenu.
    • Protect Skin Tone (man icon): Select this option to preserve skin tones from distorting when scaling.
  4. Click and drag one of the handles of the scale box that surrounds your layer or selection to resize your image.

    You can upscale (make your image bigger) or downscale (make your image smaller). You can also use the Horizontal and Vertical Scale numerical fields on the Options bar. Select Maintain Aspect Ratio to keep the scaling proportional (chain icon).

  5. When you have completed your scaling, double-click inside the scale box, or press Enter (Return on the Mac) on your keyboard.

    See the difference between a layer resized with Content-Aware Scale and a layer resized with Free Transform? Note how there is less distortion with the first method.

Chromatic Aberration

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One defect noticeable in isolated highlights or along strong luminosity edges is chromatic aberration. There are two kinds, axial and lateral, and in lenses it is the lateral aberration that is common.
Just like a glass prism dispersing a beam of light into a rainbow of colors, when different colors of light travel at different speeds in a medium (air , water etc.)  on to the sensor, the red, green and blue colors having different wavelength result in chromatic aberration. This has two major effects on the sensor too. Each channel (usually R, G, B) is blurry because it integrates a certain range of wavelengths that are imaged at different positions on the sensor. Photographic lenses comprise various dispersive, electric glasses. These glasses do not refract all constituent colors of incident light at equal angles, and great efforts may be required to design an overall well-corrected lens that brings all colors together in the same focus. Moreover, the different channels are shifted with respect to one another. This usually yields colored fringes along edges with a high level of contrast.

Chromatic aberrations are those departures from perfect imaging that are due to dispersion. Whereas the Seidel aberrations are monochromatic, i.e. they occur also with light of a single color, chromatic aberrations are only noticed with polychromatic light.

The role played in this by sensor blooming  is disputed, and is probably tied to a different aberration known as “purple fringing.” Lateral chromatic aberration shows itself as two opposed colors, usually red-cyan or blue-yellow, and is increasingly common because of wide-range zooms, which are difficult for lens manufacturers to correct across the range.
(Images courtesy of DxO Labs)