How to count EFFECTIVE number of pixels in a photo

Started 5 months ago | Questions thread
OP il_alexk Senior Member • Posts: 2,879
Re: How to count EFFECTIVE number of pixels in a photo

il_alexk wrote:

Thank you for the lovely debate, you really help me to get a better understanding of the matter and I am learning as we speak. 🤦🏻‍♂️😂

ProfHankD wrote:

MTFMapperon an ISO sequence of test images. In theory, loss is the same independent of scene photographed, although in practice that's not quite true because MTFMapper computes based on a monochrome image. Resolution is very color dependent for cameras using a CFA, nearly 2X for green what it is for blue or red; for that matter, lens resolution generally decreases for longer wavelengths due to diffraction, so red resolution is typically less than blue. If you're trying to be very precise, this can be a very deep rabbit hole.

I need to rethink this whole approach over. Maybe not entropy, hope I will come up with a more practical approach than the artificial b&w mtf metrics that's a real pain to measure.

Finally figured it out. KISS principle rules!!!


So I am considering to downgrade [from A7R3] to A7III with 24Mp pixels
My 44Mp images at ISO6400 obviously lose details compared to, say, ISO 100. Plus I lose more details after denoising. So how many meaningful pixels is effectively left? Wouldn't it be great to have a research paper that studies effective image resolution vs ISO?


Just got one of those "Eureka" moments.
A quick glance at DPR Image Comparison Studio reveals that even at ISO6400 A7RIII resolves slightly more details than A7III at ISO100 and significantly more than A7III @6400. Easy to see by looking at lines starting with "difficulty and attractions".

So, answering my own question:

  1. Low light, ISO6400 - A7R3 images have details that can be stored in 24 or slightly more megapixels
  2. Yet @6400 a7III camera with 24Mp still resolves less details compared to A7RIII 
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