Testing, Testing - Adobe Photoshop

Now go back to the original image and reduce the noise a little. Then run a few noise tests on it and compare it to the original.

  1. Open Ocean.tga and go to Image > Mode > Lab Color.
  2. Click the Channels tab in the Layers palette to show the Lightness, A and B channels.
  3. Click the Lightness channel.
  4. Run a despeckle on the Lightness channel by going to Filter > Noise >Despeckle, like you see in Figure below.
  5. You can run despeckle on this a few times, but be careful not to over blur it.

    The result is a cleaner image. To get rid of some of the color noise, I ran a despeckle on the composite image for good measure. You can see the comparison in Figure below. It may seem like there isn’t that much difference between the two images, and it’s easy to wonder if the plate is clean enough. You can perform three noise check points that make the noise apparent and let you know if there is too much noise.

    Side by side, you can see that just that the simple despeckle worked wonders compared to the original on the right.

  6. The first test: Simply increase the saturation by 50.
  7. Take a look at Figure below. You can see that this simple test has already brought up the grain in the form of a pebbly overall color. This is not always apparent to everyone, so the next step helps define the noise to those who are having a hard time seeing the noise now.

    The saturation already is showing quite a difference

  8. Apply the same Unsharp mask you did in the previous section, with these settings:
    • Amount: 150 percent
    • Radius: 2 pixels
    • Threshold: 4 levels
  9. Compare the two photos in Figure below again, the original is on the right. You can clearly see the noise now, especially in the sky. Notice how spattered the original looks compared to the cleaned version on the left. Still unsure of how to determine how much noise is too much noise? The Find Edges filter helps make this crystal clear—pun fully intended!

    Wow, look at how the grain difference really shows with the Unsharp mask.

  10. Run the Find Edges filter on your saturated and sharpened image.

You can truly see a difference in Figure below. Notice that the clean plate is not completely blank. If you were wondering how much noise is acceptable, the image on the left is a good example. The image on the right, the original uncorrected image, is a good example of unacceptable amounts of noise.

The Find Edges filter shows how your simple correction really paid off.


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