digital noise

Quick Digital Imaging Tip 25/101: Reduce Noise for Cleaner and Also Softer Images


This is tip #25 of 101 digital imaging tips I plan to post here over the next few months. Stay tuned.

Today's tip: Reduce noise for cleaner and also softer images.

As the ISO increases, so does the amount of noise in a digital image – especially at high ISO settings, and extra especially in low light situations. Long exposures also add to noise in a digital file.

Also, low-end digital SLRs have more noise at high ISO settings than high-end digital SLRs. In addition, compact digital cameras have more noise than digital SLRs when set to the same ISO – due to the smaller size of the sensor.

Reducing noise is easy. One method is to use the in-camera noise reduction feature, but that slows down the shooting rate. A more popular method is to use a noise reduction program or plug-in.

For this HDR image, taken before 6 AM in very low light in a Buddhist temple in Cambodia, I had my 5D Mark II set at ISO 1000. As good as the camera is at delivering low-noise images, the resulting file did have a bit of noise – due to the very low light and relatively long exposure (several seconds).

As an aside, this image looks very soft because there was no direct light – only very soft, diffused, low light. The light level was so low, in fact, that I had to use the LCD illumination button on my camera to check my settings. In this image, the mood and feeling is most important.

I first created this HDR image with Photomatix, and then enhanced it in Topaz Adjust. In Topaz Adjust, I used the Noise reducing feature in that plug-in. It worked quite well at cleaning up the image.

When you reduce noise, you also reduce the sharpness of an image. Check out the image below.
For this image, taken in Bodie State Historical Park in California, I reduced the noise (again using the Noise feature in Topaz Adjust) to the point where the detail in the image was lost – creating a painterly-type image. Try this effect. You may like it.

For info on Topaz Adjust, which also offer Topaz DeNoise, click here. You can save a bundle by ordering a bundle :-)

For info in Photomatix, click here.

Explore the light,
Rick

P.S. A note on noise: My dad used to say: If a picture is so boring that you notice the grain, it's a boring picture.

Beware of Banding, Notice the Noise, Forget the Filter & Raw Rules!


I got the idea for this post after receiving the latest issue of one of my favorite magazines. Great images, as always. However, I was a bit surprised to see that one of the low-light images, great as it was, showed visible and obvious banding.

• • •

One of the reasons why I use a high-end digital SLR (currently the Canon 5D Mark II and Canon 7D) is to get the cleanest possible image, that is, an image with as little noise as possible. I like to keep it clean, so to speak.

In my quest for a clean image, I always shoot Raw files, and use the lowest possible ISO.

In addition, I strive for the best in-camera exposure, trying not to underexpose the image, which can add noise to an image, especially in the shadow areas.

At its worst, underexposing can cause what is called "banding" in a file – an effect in which you can actually see the bands of pixels. Banding, by the way, is exaggerated with JPEG files, which is another reason for shooting Raw files. (But as someone just pointed out (and reminded me) on twitter, you can get banding even with a Raw file if it's poorly exposed and processed.)

I actually don't have a good example of banding because, again, I strive for the best in-camera exposure - always checking the histogram on my camera's LCD monitor. So, in an effort to illustrate banding (and noise), I opened up the shadow areas from one of by Botswana images using Curves. The long white boxes illustrate the most visible bands in the picture, which you probably can't see because it's a low res file.

I used this image to illustrate this point: If you underexpose a file too much and try to open up the shadows, you'll get an image with noise and banding.

About my properly exposed elephant image: check out the tonal range. The sun in not washed out and you can see into some of the shadow areas. This is an example of why I say, "Raw Rules!"

Speaking of noise, if you do have a noisy image, Topaz DeNoise does a great job of reducing it.

On another topic, check out the ghost image of the sun in the top picture. It was actually in the bottom picture, too, but I removed it with the Burn Tool and Clone Stamp tool in Photoshop.

The ghost image was caused by the sun reflecting off the front element of my lens and then bouncing back onto my UV filter. This is when I leaned that you gotta remove all filters when shooting into the sun :-)

Explore the light,
Rick