Question: I recently bought my first DSLR and made the decision to spend a similar amount on the lens as on the body, on the basis that the lens is where the optics are, and I would guess that changing the optics make a much greater difference to image quality than changing the sensor. Camera reviews seemed to implicitly confirm this suspicion, because they seem to focus much more on features than on image quality, and when they do discuss image quality it mostly seems like a review of the kit lens rather than the body itself, at least in the case of the entry level DSLRs I was looking at.

But now I'm curious: what effect *does* the body have on image quality? I'm not asking so much about things like APS-C vs. full-frame, in-body image stabilisation, ISO range or resolution; things like that have well-defined effects that can easily be compared "on paper". I'm asking more about whether the body imparts any of its own special character to images in the same way that lenses do. In other words, can two bodies with similar specs differ in the quality of image they can produce with the same lens? I'm asking mostly from curiosity, but it would be a useful thing to know if I'm choosing a camera again.

Answer: 
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> What effect does the body have on the character and quality of images?
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After you eliminate "... things like APS-C vs. full-frame, in-body image stabilisation, ISO range or resolution..." there's not much left. Sensor size, pixel size, sensor efficiency (how much of the light that hits a sensor actually makes it down a pixel well and gets counted), etc. are the primary determining factors in how images of the same scene recorded through the same lens by various sensors differ. Sensor design decisions for things such as on-die noise reduction or post analog-to-digital conversion noise reduction will also affect things to a degree. On-die NR tends to "eat stars" by eliminating weaker stars along with noise in cameras that do more noise reduction on the analog signal before it is converted to digital. They also give cleaner shadows when the shadows are pushed, for the same reason.

When people say things like Canon cameras tend to have warmer skin tones while Nikon's skin tones are cooler they're really referring to decisions made with regard to the way the camera's firmware converts the raw data coming off the sensor into color information.
Probably we can narrow them into

* Noise 1. I would not discard ISO range. This is one of the most important things. Ok I am not refering on the maximum ISO directly. But if a camera has a higher ISO sensitivity, for example one with a max ISO of 1,600 and one with max ISO of 64,000, the second most likely will perform better on the same ISO 1,600.
* Noise 2. Some cameras have a slight pattern visible in low light conditions. This changes how you can manipulate an image, for example underexposing it and recovering detail in the shadows.
* This is related to dynamic range. Some cameras could show more detail on the shadows and the highlights than others.
* Color rendering. This could depend on some processed data, like shooting directly on jpg. But also some shoots on raw could see more detail on one color than others. Take a look at this page <https://www.dpreview.com/reviews/canon-eos-1d-x-mark-ii/6>, where you can compare a standard target between diferent camera bodies. If you choose the same brand you probably minimize the lens variable.
* Some sharpeness. Some sensor arrays are more optimized per square area than others, so that can give some diferences in sharpness.