Digital Underwater Photography

Sharpening

There are a many methods to sharpen your image. In this section I will introduce three of them. You can apply the sharpening to the entire image or create a mask to apply it selectively.

To sharpen and Image using Unsharp Mask Filter

Unsharp Mask Dialog Box

The Unsharp Mask sharpens an image by increasing contrast along the edges in an image. Select Filer Menu > Sharpen submenu >Unsharp Mask. The Unsharp Mask does not detect edges in an image. Instead, it locates pixels that differ in value from surrounding pixels by the threshold you specify. It then increases the contrast of neighbouring pixels by the amount you specify. So, for neighbouring pixels the lighter pixels get lighter and the darker pixels get darker. In addition, you specify the radius of the region to which each pixel is compared. The greater the radius, the larger the edge effects. As a general default you can use the following values: Amount: 85%, Radius: 1, Threshold: 4. A note to watch for: oversharpening your image may produce a halo effect.

To sharpen an image using High Pass Filter

  1. Open your image and unless already visible, select Window > Layers to show the Layers palette or simply press F7.
  2. Duplicate the background layer by hitting Ctrl+J, selecting Layer > Duplicate Layer command or by dragging the layer onto the New Layer icon at the bottom of the Layers palette.
  3. With the duplicate layer selected, select Filter menu > Other submenu > High Pass.
  4. Enter a radius value between 5 to 12. 9 is usually a good choice and click OK.
  5. Still in the Layers palette, change the layer blending mode to either overlay, soft light or hard light, depending on the image and amount of sharpening wanted.
  6. You can also change the layer opacity of the duplicate layer until you happy with the result.
  7. Flatten the image by selecting ‘Flatten Image’ command from the fly-out menu on the Layers palette.

I usually prefer working with this method than using the Unsharp Filter as the results are affecting another layer instead of my original image and I have more control on the blending modes and opacity. Yet one disadvantage of this method is an image with a lot of background noise. The background noise could be a result of a high ISO setting which is common if you shoot on Program mode and let your camera selects the ISO setting automatically. It can also be due to backscatter in silty waters. In any case, this method will enhance the background noise even more. One way to work around this problem is by applying a selection mask to selectively sharpen some areas of the image.

To sharpen an image using LAB Mode

  1. Open you Image.
  2. Select Image > Mode > Lab Color.
  3. Unless already visible, select Window > Channels command to show the Channels layer.
  4. Click on the Lightness channel to select it
  5. Select Image > Adjustments > Levels to open the Levels dialog box (or press ctrl/cmd+L). Click on Auto Levels on the right and then click OK.
  6. Select Filter > Sharpen > Unsharp Mask, enter the values as needed and click OK.
  7. Select Image > Mode > RGB Color.

This method can sharpen your image creating halos effects or noise artefacts and without losing any detail in the image.

Sharpening Tips

  • Sharpen your image on a separate layer so that you can resharpen it later, if you need to output it to a different medium.
  • If you sharpen your image on a separate layer, set the layer’s blending mode to Luminance to avoid colour shifts along the edges.
  • Sharpening increases image contrast. If you find that highlights or shadows are clipped after you sharpen, use the layer blending controls (if you sharpen a separate layer) to prevent sharpening in highlights and shadows.
  • Sharpen your image multiple times in small amounts.

Blend Effects

The Fade command changes the opacity and blending mode of any filter, painting tool, erasing tool, or color adjustment. Applying the Fade command is similar to applying the filter effect on a separate layer and then using the layer opacity and blending mode controls.

  1. Apply an Unsharp Mask filter to an image or a selection.
  2. Select Edit > Fade. Select the Preview option to preview the effect.
  3. Drag the slider to adjust the opacity, from 0% (transparent) to 100%.
  4. Choose a blending mode from the Mode menu.
  5. Click OK.

Further Resources

Back to Top

© Design by Elle