What is a reasonable approach for assessing and comparing image quality, visually, when you have two different sensors, each of which is the same size but significantly different number of pixels or resolution (same thing?)Would you scale the image size based on resolution, or just view at the same % even though the image sizes will be different, or ???The most obvious example is the 12MP sensor used by Sony in the A7S with the 20MP sensor used in a Canon 6D - both of which are "full frame" and about the same dimensions.Rick

Shoot a scene with the two cameras with as little time as possible between the shots. Use the same lens for both shots (if comparing a Canon, you will need a Canon adapter). There should be less than 2 minutes between the shots, as light is always changing.Make a large print, perhaps 20x16 inches or A1 size from each shot. Compare.If you can't make a big print, crop down to the same section of the images (perhaps a quarter of each) and make smaller prints.Do not resize or rescale, as the images are then no longer what the cameras produce.

I would say: Take two exposures of the same scene with the same lens with as little time difference as possible. Be sure the light is the same, and so the exposure settings. Then fully process the files to exactly the same color, contrast and tonal distribution, since different sensors/raw files will have different "flavours". NOTE! This is extremely important, since this will even out the difference and will tell what each camera is capable of for real world use. Print the files at the same size, say A2 or larger. Or scale the files to the same pixel dimentions and then view them side by side.

RickColman wrote:What is a reasonable approach for assessing and comparing image quality, visually, when you have two different sensors, each of which is the same size but significantly different number of pixels or resolution (same thing?)Would you scale the image size based on resolution, or just view at the same % even though the image sizes will be different, or ???The most obvious example is the 12MP sensor used by Sony in the A7S with the 20MP sensor used in a Canon 6D - both of which are "full frame" and about the same dimensions.People always seem to be looking for a way to pick the "best" equipment.Well, that's utter nonsense.There is no such thing as the one, universally best, anything. (Ok, maybe the men's and women's basketball teams at the University of Kentucky are exceptions....)  Best really depends on your precise application: there often is such a thing as the most suitable for a particular set of image-making circumstances.For example, best-case dynamic range from even the APS-C Sonys simply outclasses Canon's best FF cameras, and DR isvery important, so why does anyone even consider using a Canon? Then again, Canon DSLRs get somewhat longer battery life per charge, so you could argue that IQ of shots with terrible DR is infinitely better than having a Sony that can't take pictures because the battery died.Horses for courses-- decide what your circumstances need and score based on that... and different circumstances get different scores. This is why sites like DxO and DPReview don't just quote one number (although both do summarize to one number based on their weighting of performance factors, a number that sophisticated users don't really pay much attention to).

People always seem to be looking for a way to pick the "best" equipment.Well, that's utter nonsense.There is no such thing as the one, universally best, anything.I dont think I ever used the term "best"  ...I have a perfectly good Canon 6D that I was using for landscape astrophotography.Never one to leave well enough alone, I purchase a Sony A7s expecting a major improvement in night handling and a minor improvement in image quality for the type of stuff I do.My attempt to compare image quality is to determine whether I got anything for the extra money.I think that is reasonable.

HelloMy advise, make pictures of things you also shoot normally.use the same or similar lens if possible under the same condition.use the same software for development of the picturesuse the same print or screen you always usethan decide what you like most.I do not care for test and resolution charts to much,to get an idea ok but the final call is on what you like and usehope that helpsRegards

You down-res the higher mp image to the lower and then compare them at 100%.That assumes that you can create an even match-up with lenses, iso, light, exposure parameters, shot discipline, etc.

RickColman wrote:People always seem to be looking for a way to pick the "best" equipment.Well, that's utter nonsense.There is no such thing as the one, universally best, anything.I dont think I ever used the term "best" ...No, you said "What is a reasonable approach for assessing and comparing image quality" without specifying a specific context in which you wish to judge IQ. That presupposes that there is a better of two, or best overall, consistent across all contexts, which is not how this stuff works. Beyond that, you can't reasonably summarize all common IQ test methods in a posting to a DPReview forum -- that is done by thousands of technical papers published by hundreds of authors.I have a perfectly good Canon 6D that I was using for landscape astrophotography.Never one to leave well enough alone, I purchase a Sony A7s expecting a major improvement in night handling and a minor improvement in image quality for the type of stuff I do.Did you get the expected improvement in night handling?The best way to judge IQ "for the type of stuff" you do is to try doing it with both and compare the resulting images as you would normally view them. You might be able to figure-out which standardized tests correlate best with the IQ you see in your testing, and thus know which standardized tests to look at before you have the cameras to try for yourself... but you have them now, right?My attempt to compare image quality is to determine whether I got anything for the extra money.I think that is reasonable.I get it; it's quite reasonable and it's an emotion called "buyer's remorse." You spent a pile of money when you "have a perfectly good Canon 6D" and thus you want external validation that it was money well spent. For some of us, it's a need to have excuses to tell the spouse.Relax. The Canon 6D has more pixels than the Sony A7S and I suppose you might run into the lossy raw issues (although you can use my freeKARWY tool to fix things like star trail issues), but in every other IQ dimension I can think of, the A7S walks all over the 6D and DxO backs that up nicely.In sum, I'm really not trying to give you a hard time here -- I'm telling you to trust your own eyes making the comparison however you normally would compare your photos even if they were taken with the same camera.