Why Lower Resolution Sensors Are Not Actually Better in Low Light
There is a purveying thought that larger resolution sensors, with therefore smaller pixels, are worse than lower resolution sensors, with therefore larger pixels, in low light. This is a myth.
Chris Niccolls and Jordan Drake from DPReview TV have published a video that succinctly explains how this myth was perpetuated for years and, arguably, still continues to this day. The thought was that when a photo taken with a camera with a lower resolution sensor was compared to another taken with a higher resolution sensor at 100% side by side, the lower resolution sensor looked better.
But Niccolls says that the issue is the comparison at 100%. If instead, those two photos were compared in full screen or printed out and compared side by side, the advantage of the lower resolution sensor would not be apparent.
Another major contributor to the myth was the arrival of the Sony Alpha 7S, a full-frame 12-megapixel camera produced to perform exceptionally in low light. The “S” in the product name stands for “sensitivity,” after all. Because the camera had a lower resolution sensor — a decision which was made for various reasons, as Niccolls explains — the myth of linking low resolution to high low light performance was exacerbated. One of the main reasons the Alpha 7S did so well in low light was not due to the low resolution, but because it was one of the first dual gain sensors released into a consumer camera. Now, multiple dual gain sensors are used in digital cameras, which Niccolls says has resulted in a more level playing field once again.
To illustrate the point, Niccolls and Drake compare two Sony cameras: the Alpha 7S Mark III and the Alpha 7R Mark IV. The reason these two cameras were chosen was that they are both from the same manufacturer, both from the same “generation,” and both have backside-illuminated sensors. Rather than rely on just digital pixel peeping, the two took their results from the test to a print shop to see the images side-by-side on paper under controlled lighting.
When printed at 11 x 17 inches, the photos don’t show much difference — if any at all — when it comes to color noise. The Alpha 7R IV, with its higher resolution, actually stands out thanks to its better detail rendition.
Printed larger at 22 x 33 inches, the Alpha 7S Mark III shows more obvious color noise than the Alpha 7R Mark IV.
“I think if you’re talking same generation of sensors, similar kinds of cameras, I think we have dispelled the myth that lower megapixels means better low light, because that’s not necessarily the case,” Niccolls says.
Niccolls says that if two photos taken on both cameras were compared at 100% resolution side by side on a computer, the Alpha 7R Mark IV absolutely would show more noise. But he argues that people don’t look at images at 100%, only pixel peep there. Otherwise, people look at photos full screen on a panel or full size on a print. In that regard, the difference is much less obvious.
The main goal for the duo in this video was to dispel the idea that low-resolution sensors are always better in low light. There are of course advantages to low-resolution sensors, especially when it comes to video performance. Additionally, lower resolution cameras tend to be more popular for sports and journalism, where it can be easier on processors and editing pipelines to have smaller photo files. That said, technology is advancing to the point where it is easier to deal with more data, and when it comes to pure image quality and options with photos, Niccolls argues that more resolution is — generally — better for photographers because it gives them more options to work with a file than lower resolution cameras.