Why do my photos suddenly look noisy and blocky on my computer?
Asked 9/20/2011
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2 answers
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I’ve recently noticed much more visible grain/speckling and a loss of detail in some photos from my EOS 30D with a Sigma 18-125mm lens. One shoot was at high ISO, but on another I used a low ISO and added flash, yet I still saw speckled backgrounds and areas that looked like a low-quality JPEG. The files are RAW, and detail seems present on the camera LCD. A colleague opened the same image on another computer and it looked normal, so this now seems like a viewing or software issue on my system rather than the camera or CF card. What could cause this, and what should I check?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
4
High ISOs don't cause noise, lack of light causes noise. If you decrease the ISO without doing something to address the level of incoming light (note if you shoot in one of the auto modes your camera will do this for you) your signal to noise ratio will get worse.
There are a few other contributory factors, for example if the sensor is left on for a long period of time and becomes hot e.g. using live view then noise can increase.
Your post processing regime also contributes, if you pull the shadows up a lot then you will see a lot more noise.
But the major contributory factors in noise are "shot noise" due to the random emission of photons from a light source and not collecting enough photons to even out the randomness, and electrical noise from the sensor itself.
Both of these get better with more light (by capturing more photons the signal produced is stronger with respect to the electrical noise). The fixes are to use a longer shutter time (and tripod if necessary), open the aperture more, or use an external source of light such as a flash.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
15y ago
0
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A CF card is very unlikely to cause this. Since the same RAW file looks fine on another computer, the most likely cause is your computer’s display or image-viewing setup, not the camera sensor.
Things to check:
- Display color depth/settings: if your system has dropped to 16-bit color, you can see banding, blocky color areas, and poor gradients.
- RAW conversion/rendering settings in Lightroom/Photoshop or your OS codecs.
- Monitor/profile/configuration issues.
About the “noise”: high ISO itself isn’t the root cause; low light/low exposure is. Noise becomes more visible when the signal is weak, such as in underexposed areas or when shadows are lifted in processing. Lowering ISO without increasing actual exposure can make the signal-to-noise ratio worse, not better.
So in your case, there are likely two separate issues:
- Normal visible noise from weak exposure/shadow recovery.
- Abnormal blocky rendering caused by your computer’s display/software settings.
Start by checking display color depth, monitor/profile settings, and how the RAW file is being rendered on your machine.
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