Image noise consists of distracting grainy or colored pixels in the image, caused by high ISO settings, long exposure times, warm sensors, or small sensors. There are luminance and color noise types. Noise can be reduced by using low ISO, short exposure times, good sensor quality, cooling, shooting in RAW, and post-processing with modern algorithms. The ETTR strategy recommends slight overexposure for images with less noise.
Category: Photography Basics > 3. Exposure & Camera Settings Article ID: 3.14 Created: May 2026
Key Points in Brief
- Image noise is grainy, colored interference in the image – especially visible in dark areas and at high ISO settings
- Causes: high ISO, long exposure times, warm sensor temperature, and small sensors
- Noise can be reduced by low ISO, short exposure time, good sensor, and post-processing – it cannot be completely avoided
Explanation
What is Image Noise?
Image noise refers to visible disturbances in a photo: grainy spots, colored pixels, or irregular brightening that were not present in the original scene. It is the most common image flaw in digital photography and resembles the grain of analog film.
There are two main types:
- Luminance noise: brightness fluctuations from pixel to pixel → appears grainy, similar to film grain
- Color noise: colored pixels (red, green, blue) in otherwise uniformly colored areas → appears blotchy, more distracting than luminance noise
Causes of Image Noise
1. High ISO setting (most common cause) A high ISO means the camera signal is electronically amplified. The more it is amplified, the stronger the noise becomes. The ISO level at which noise becomes visible depends heavily on the sensor:
- Smartphones / compact cameras: often from ISO 400–800
- APS-C cameras: good up to ISO 1600–3200
- Full-frame cameras: often acceptable up to ISO 6400–12800
2. Long exposure times Every sensor heats up during exposure. From about 0.5–1 second, thermal noise can become visible. For long exposures lasting several minutes, it is significantly pronounced. Warm ambient temperature increases this effect.
3. Small sensors Small pixels collect less light. The weak signal must be amplified more → more noise. That is why smartphones and compact cameras produce more noise at the same ISO compared to full-frame cameras.
4. Post-processing Brightening an underexposed image during editing significantly amplifies visible noise – dark image areas are especially susceptible. The same applies to digital zoom and heavy sharpening.
5. Electronic viewfinder (Live View) The sensor warms up when it is continuously read out for monitor operation. For critical night shots: turn off the monitor early and only activate it shortly before the shot.
Hot Pixels
Hot pixels are single bright glowing pixels that appear during long exposures or high ISO – an overheated pixel transmits a false, overly bright value. They can usually be easily removed in post-processing or fixed by camera firmware updates.
Not to be confused with stuck pixels – permanently defective pixels that always display the same incorrect color value.
Reducing Noise – Key Measures
Before shooting:
| Measure | Effect |
|---|---|
| Keep ISO as low as possible | Most important measure against noise |
| Use a tripod + longer exposure instead of high ISO | Same brightness, less noise |
| Fast lens (wide aperture) | More light → ISO can stay low |
| External flash | More light instead of high ISO |
| Shoot in RAW | More flexibility for noise reduction in post-processing |
| Keep camera cool | Reduces thermal noise |
In post-processing:
- Modern RAW editors (Lightroom, Capture One, Darktable) have very good noise reduction algorithms
- Reduce luminance noise: smooths the image, costs some detail sharpness
- Reduce color noise: almost always recommended, hardly any loss of detail
- AI-based noise reduction (e.g. Lightroom Denoise, Topaz DeNoise AI) delivers impressive results
Important: In-camera noise reduction (JPEG) automatically smooths the image but can remove real details. For maximum control, shoot in RAW and edit yourself.
Practical Tip
The Expose To The Right (ETTR) strategy: Slightly overexposing (pushing the histogram as far to the right as possible without clipping) usually yields images with less noise. Bright pixels contain more signal than dark ones – and can be darkened better in RAW editing than brightening dark areas. Use only with RAW, not JPEG.