Cleaning up images, example two

Here's our second tutorial on how to deal with high ISO images. Some of the edits I will do here are specific to problems with my S85 and even this particular picture, but the basic ideas will carry over for images from any camera model. This tutorial assumes that you have a copy of Photoshop 6.

All text and images are © 2001 by Ronald Parr.

Getting started

This time we'll use an image from my first portrait gallery. It's image 2069. You can download the full image with the original exif header here. This is a shot of a child playing in a mixture of natural and artificial light. I needed the fastest shutter speed possible to catch the action, so I bumped up the ISO to 400. This afforded me only 1/40 sec. shutter speeds, but this was the best I could do. You'll notice some motion blur in the a few of the shots in the gallery.

The original picture has many problems. The colors are off and there is a lot of noise. Let's see what happens if we ignore the noise and try to do a reduction to web size:

Reduced (bicubic) Reduced then sharpened Our final result

We see that the a simple reduction still contains a good bit of noise (look at the dark wood on the top left) and isn't very sharp. If we try to sharpen it up with the default Photoshop sharpening filter, things get a little crisper, but also significantly noisier.

Compare either of these with our final result. Notice that the wood floor is smooth and shiny, but also detailed. The dark wood in the top left is noise free. The child's eyes are shiny and clear and her complexion is smooth and natural.

Now we'll see how to go from our noisy original to our final result, fixing some of the color cast problems along the way.

Getting to the source

The source of the noise problems in the reduced images is the noise in the original image:

The color noise here is very bad. We see the characteristic S85 red pitting in the shadow areas of her turtleneck and lots of random color noise on the left of her cheek.


You've probably noticed that original image has a slight red color cast to it as well as a slightly hazy look. The red toy hammer has got a strange, almost glowing quality to it. This is not the natural color.

We're going to address the color problems before we address the noise problems. Why? The noise reduction method we're going to use tries to smooth out random color noise and the extent to which a pixel looks noisy will change as we shift the colors around.

The natural thing to try here is Photoshop's auto levels command. Here's the result:

This improves the color somewhat, but it also makes the red hammer look even more outrageous. We fix this by turning down the saturation -20:

The astute reader with a good monitor may notice that this process has clipped the reds slightly. We'd probably be better off starting from scratch and adjusting the colors without auto-levels, but the results we'll get here are good enough for our purposes. Notice that the desaturation has itself reduced some of the apparent noise in the turtleneck and the baby's cheek. Unfortunately, a slight green cast (more noticeable when you see the entire picture) has crept in now, so we go to variations, move slider to the second setting from the left and add one click more magenta:

Here's a summary of what we did:

Original Auto levels Desaturation (-20) More magenta

Now we're pretty happy with the color and it's time to go after the noise.

Noise reduction

We're going to start again with Jes's color grain reducer. I discovered this in a thread on dpreview. I used the heavy smoothing option for this one:

Before After noise reduction

Notice that the color noise on her cheek and her turtleneck has improved dramatically. The improvement is even more evident if we look at a darker area:

Before After noise reduction

What's great here is that no detail appears to have been lost. In fact, this action is so conservative that it still leaves behind some luminance noise. We're going to clean this up by using despeckle:
Before After despeckle

This operation may have cost us some detail, but it's still a bargain. (We might reconsider if we needed to use a larger size image.)

The home stretch

Now we're ready to reduce the image to web size (640x480). We use bicubic resampling in Photoshop:

The result is quite good, but it isn't sharp, so we need to apply a sharpening filter. We could use the default Photoshop sharpening filter or try something a little smarter like Fred Miranda's free sharpening action (small file setting). Let's compare the results:

Before Photoshop default sharpening Fred Miranda's sharpening action

Photoshop's default does OK, but Fred's action really shines here. Notice that the Photoshop filter has amplified the remaining noise in the wood on the top left, while Fred's action preserves a clean appearance for the wood and even gives it a natural looking shine. The baby's skin has a slightly textured look in the Photoshop filter example, but it's smooth with Fred's action. Despite preserving the basic textures better, Fred's filter also has more apparent sharpness. The baby's eyes are crystal clear and her hair is both sharp and natural looking. For the first time, even the plastic hammer gets a very realistic appearance.

We've done it again, transformed a messy ISO 400 image into something worth sharing.

Ron Parr
Last modified: Tue Dec 11 20:48:12 EST 2001