Quick Reference: Using “Clamp” in Cycles

Being that my current machine isn’t nearly as meaty when it comes to processing as I’d like – and doesn’t have a graphics card that is compatible with Cycles GPU rendering – I’m always looking for ways to improve performance when rendering in Cycles. Blender Guru has a post worth checking out, 4 Easy Ways to Speed Up Cycles, but I’d like to mention a simple technique I’ve just recently discovered, using the Clamp setting.


Using Clamp

This example is still a work in progress, but is suitable for demonstrating the use of Clamp. (You can view the final image here in my portfolio.) The scene is lit by two emitter planes and a HDRI map. The bounces are already set to pretty conservative levels, but it’s till firefly city. Here’s a render after 2642 samples with Clamp set to 0, using progressive refine so the whole image renders at once (I won’t tell you how long it took on my computer, it’s a little embarassing.)

2642 Samples, Clamp set to 0

In the Render panel, under Sampling, there is an option called Clamp (more on the particulars of what this does below.)  By setting the “Clamp” to 2, this is the result after 1363 samples.

1363 Samples, Clamp set to 2
1363 Samples, Clamp set to 2

You’ll notice that the image is a little dimmer and duller, the colors are less vibrant. That is easily fixed in the compositor with a simple Color Balance node. I essentially want to increase the contrast and brighten the image. Also, might as well do a little color correction while we’re at it.

With Color Balance node, reduce the value of the Lift and increase the value of the Gain
With Color Balance node, reduce the value of the Lift and increase the value of the Gain

With a little post-processing, an image that is less muddy. I’ve reversed the dimming effect of Clamp and added some flair to the image that I would have done anyway, at the same time. A bit more refinement of the image is a good idea, but this illustrates the basic point.

1363 Samples, Clamp set to 2, Color Balance adjusted
1363 Samples, Clamp set to 2, Color Balance adjusted

So, utilizing the Clamp setting, I was able to get a render that is virtually noise-free in about half the render time. You’ll have to experiment to find a Clamp value that balances render time and image quality for each scene. Remember that using clamp will dim the image (particularly the highlights) but that is usually fixed pretty easily with some post-processing. (You’ll notice the paper on the mini notebook has blown out a bit, this can be fixed by making the texture darker.)

Why Use Clamp

For more detail on Clamp, as well as other noise reduction techniques, explanations on how they work and what causes noise in the first place, I suggest checking out this page in the Blender Wiki. Briefly, Clamp caps the value of each sample, easing fluctuations from pixel to pixel. This obviously reduces the physical accuracy of the final image and dulls the brighter highlights, but these issues are usually either negligable or easily corrected.

I chose to use Clamp over using Filter Glossy or other techniques to reduce noise in this render for three main reasons:[list icon=”plus”]

  • It’s faster, easier and more effective at noise reduction over the entire image
  • Given the amount of glass and liquid as well as their prominence in the image, I wanted to preserve the accuracy of those light interactions as much as possible
  • It doesn’t involve making adjustments to individual elements or shaders


Disabling caustics removes entirely a real physical effect of light (though it often doesn’t appreciably diminish the quality of the image and is a good idea to use in conjunction with setting a Clamp value), while Filter Glossy forces a reduction in sharpness. With Clamp, the inaccuracy is mostly in the intensity of highlights.

13 thoughts on “Quick Reference: Using “Clamp” in Cycles

  1. Pingback: Использование Clamp в Cycles

  2. The Ideal Place to Install a Wireless Router Device.
    The remaining pins all have different functions which include providing power for each HDMI cable, ensuring the
    smoothest transmission possible from one device to the next, and
    much more. Others are more fitted and highly styled, to wear with business
    office attire or evening wear.

  3. Right from the way they approach the problem, to the way they speak and the assurance that they provide and their experience speaks volumes about the company.
    Different kinds of windows need various cleaning mechanisms.
    If you find a company that seems as though it
    only serves high class buildings and multi-story buildings, you may
    think they won’t clean your windows if you only own a small building, this isn’t true.

  4. but I want to talk to you for a minute and I couldn’t think of what else to say.
    Dance classes can help you in making a routine and learn new dances that will help you be a better performer.
    Unfunny, annoying and genuinely unpleasant is the only way to describe it.

  5. One of the reasons your special day will be even better when you are in your Bachelor
    party Limousine is because this will be a great chance to take
    photos and not have to worry about traffic and driving conditions.
    By visiting their websites you can find out all the details
    of available vehicles along with prices and conditions.
    If you can arrange it, visit the company and look at some of its vehicles.

  6. If you need to get your vacuum paper bags, where is the better source to get them.
    This is one of the must-have tools in home as it removes dirt from our homes and works much more professionally and
    capably than broom and dustpan. It has a Drive Steering System and Dual – Force+Suction.

  7. Acho muito boa esta estratégia,porém a defendo se for
    feita com carbos paleo e após um treino,fazendo jejum intermitente
    de pelo menos 16 horas no dia seguinte,ou seja,almoçando no dia método faz uma espécie de recarga de glicogênio,sem depositar gordura ,e reativa a leptina,
    importante hormônio que nos avisa que estamos cheios” após uma
    refeição.A leptina ascelera nosso metabolismo também.Sempre a cada 7 dias.

Leave a Reply

Your email address will not be published. Required fields are marked *