Reducing Image Noise at High ISO Settings

As the ISO setting increases, image noise becomes apparent in every camera. In crop sensor cameras, noise is often clearly visible at ISO 800, while in full-frame cameras, it appears around ISO 1600. Although cameras allow for significantly higher ISO settings, these are often avoided due to the resulting insufficient image quality.

This raises the question of how to achieve good images even at high ISO settings. 

Noise Reduction Using Multiple Images

First, we use a wide aperture and set the shutter speed to a value that allows for handheld shooting without camera shake. For star photography with a tripod, we select an exposure time of less than 15 seconds, which necessitates a high ISO setting.

The following examples were created handheld at ISO 3200.

No Tripod? No Problem.

In many buildings, especially churches and museums, photography is permitted, but with the restriction of not using a flash or a tripod. If the available light is also insufficient, capturing a good photo becomes impossible.

Capturing the Starry Sky

You have likely taken night shots with a tripod. You may have noticed that with an exposure time of 15 seconds or longer, stars begin to move, creating small streaks. If these "star trails" are not desired, an intelligent solution is also required.

Solution: The Arithmetic Mean

1. Create several identical shots with a high ISO setting. The higher the ISO setting, the greater the number of required images. In the examples, between 7 and 10 images were created using the continuous shooting function.
2. Process the images as usual in a RAW converter to eliminate chromatic aberrations and lens errors. Pre-sharpening may also be performed.
3. Apply the same settings to all images in the series and export them as JPEGs.
4. Load the images into Photoshop layers.
5. For handheld shots, align the images on top of each other (Edit -> Auto-Align Layers).
6. Select all layers and merge them into a Smart Object (Layer -> Smart Objects -> Convert to Smart Object).
7. Now, calculate the Arithmetic Mean. The function is located under (Layer -> Smart Objects -> Stack Mode -> Mean).
8. Crop and re-sharpen the final image.