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DPP: Part 2 ? Digital Image Qualities: Exercise 7 ? Your tolerance for noise

This exercise looks at the effect noise has on an image.  The requirements were an indoor, daylight scene, with a combination of sharp detail and textureless areas – with some of the textureless area in shadow.

I used my TARDIS against a wall where the windowsill casts a shadow.  The camera was set up on a tripod and I shot a series of images at 1-stop intervals along the unexpanded ISO range of my camera.  Aperture priority was used to maintain a consistent depth-of-field.

With the images done, the exercise is then to record the results of altering the ISO setting.

ISO 100

ISO 100

ISO 100

The text appears sharp and the texture of the white wall is smooth throughout.  There’s a small amount of noise visible when zoomed in on the wall shadow and the light details on the open TARDIS door. IT’s not visible when reproduced at the above “web size”.

ISO 200

ISO 200

ISO 200

At web size there are no clear differences.  When zoomed in the noise is more apparent where it was observed before – breaking up the smoothness of the shadow area on the white wall.

ISO 400

ISO 400

ISO 400

Again, there’s not much difference, though the white part on the TARDIS door does have some noise that’s noticeable when zoomed in.

ISO 800

ISO 800

ISO 800

When zoomed in, the inside of the TARDIS has areas of obvious noise, but it’s not affecting the overall image too much.  Foreground detail is still clear.

ISO 1600

ISO 1600

ISO 1600

At web size noise is now slightly visible in the shadow on the white wall.  When zoomed in the blue of the TARDIS is dotted with red and purple noise.

ISO 3200

ISO 3200

ISO 3200

Noise is now apparent in the light areas of the image and is bad across the whole image – when zoomed in.  I’d say it’s okay for reproduction at a web size still, but I’d expect the noise to be visible on a print.

ISO 6400

ISO 6400

ISO 6400

Noise has increased again, though it’s still passable at web size.  On close inspection thought it looks like a very bad camera phone image:

ISO 6400 - Close-up

ISO 6400 – Close-up

Conclusion

In this particular image, noise hasn’t significantly affected the image when viewed at web sizes.  High contrast overall has helped in the areas of detail.  However, the noise is clearly evident when zooming in on the image – and at larger print sizes the image would suffer.  The exercise has demonstrated how prominent noise can become in dark and shaded areas.

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