Why do sharp chart edges look jagged or noisy in a RAW file?

Question

I photographed a test chart and the printed edges look very clean to my eye, but in the image the edge transition looks uneven when zoomed in. I checked the RAW data and the effect is already there. This is not the edge of the frame; it appears within the image area.

I also noticed that the RAW looks different depending on how I view it: in Bayer mode it looks different than in Gray mode. Is this normal RAW preview behavior?

Is this kind of edge roughness unavoidable because of pixel sampling, diffraction, or RAW rendering, or could it indicate a poor-quality CMOS sensor?

Steven Kersting · Answer

Two things are occurring. Human perception in terms of your ability to see detail/resolution, and the importance of contrast in our perception of sharpness/resolution, are both different from how a digital sensor sees.

I.e. for a human a larger detail needs less contrast (sudden change) to be perceived equally as sharp/clean as a smaller detail. And a human cannot see down to the 4-8 micron level unaided (size of a typical sensor photosite). For example, bacteria are about 3 um in size; red blood cells are 8 um. Whereas a lens could theoretically resolve down to 1 um.

Any projected/reflected light pattern (or shadow) from a diffuse source will have a falloff gradient along it's edge. The sensor is simply recording that; it is unavoidable.

Why do sharp chart edges look jagged or noisy in a RAW file?

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