Removing Colour Banding from your images


This article is made because one my clients has problems in her photographic output. So I created this article so she and everybody can benefit from this solution/s.

Banding? What is it? Usually it is best explained visually so see the photo below.

banding

How Does it happen?

Colour banding is a problem of inaccurate colour presentation in computer graphics. In 24 bit colour modes, 8 bits per channel should be enough to render images in the full visible spectrum. However, in some cases there is a risk of producing abrupt changes between shades of the same colour. For instance, displaying natural gradients (like sunsets, dawns or clear blue skies) can show minor banding.

Colour banding is more present with relatively low bits per pixel (BPP) at 16–256 colours (4–8 BPP), where not every shade can be shown because there are insufficient bits to represent them.

Possible solutions include the introduction of dithering and increasing the number of bits per colour channel.

Colour_banding_example01

One of the things you’ll have noticed if you’re a photographer, videographer or motion graphics designer, is color banding artifacts when converting your work to 8bit web formats. This happens because each color of an 8bit image only has a color range of 256 values. So say you have a sunset that’s orange and shifts into a purple or black. Between those two colors there might not be a large enough range in color to create a smooth transition between the two shades.

Usually, you don’t notice these things in Lightroom but when you export to JPEG or H264 for the web, clour banding will appear.

And what a horrendous print it will produce!

The good news is that Photoshop’s gradient tool handles gradients pretty well with multiple colors.  Photoshop does the math and immediately rasterizes the outcome.  Through a combination of dithering and subtle noise the fade is rendered pretty smoothly.  You can even hit the levels or curves adjustments later and it looks decent.

What is the solution?

Several solutions exist.One is adding Noise

  1. If you are using Lightroom.it happens when you apply too much noise reduction or Luminosity. Noise can have a lot of variation of color that will add extra information outside the single shades 256 range. So if you notice banding a simple fix might be to add back your grain reduction. or simply just avoiding too much Noise reduction
  2. If youre using Photoshop.Use filter > Noise > Add Noise and choose uniform and check the monochromatic checkbox. . Amount is depending on what you see in the image. Dont add to much as it will show up and put more problems into your image.
  3. Use Two Color GradientsTo prevent banding while using Photoshop’s gradient tool, always use at least two colors. Fading a single color to transparency will not yield pretty results.  If you absolutely must fade a color to transparency, make sure the gradient is small, or that the range of color difference in the gradient is high.  It’s the long and subtle gradients that cause problems.
  4. Use Noise in Another LayerIf you absolutely need to maintain a lot of integrity in your photo, but still need to remove banding in some area, try adding the noise to its own layer.

    1. Create a new layer and fill it with 50% gray.  That’s about #808080 if you’re working in RGB.
    2. Place this layer above the image you’re adding noise to. In the layers palette, choose ‘Overlay’ as the blending mode.
    3. Add noise to this gray layer, 2-3% should suffice but you should look in the preview image before you commit anything.

    You’ll notice that the noise does not affect any very bright or dark areas of your image.  Because the noise is in ‘Overlay’ mode, you’re free to crank up the noise as high as needed, without destroying the quality of your highlights or shadows.

    Another benefit to having the noise in its own layer is that you can use your eraser tool to remove noise from areas where it is not needed.  You could even take one step further, creating a complex mask and applying it to the noise layer, giving you full control over which areas are affected.

 


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