Resolution: Is Higher Really Better?

Two part question:

1) Many of us casually shoot pix for fun. If we get something we really like, we print it 4x6, 5x7 or maybe even 8x10. Okay, so if my camera is has a max resolution of 8.5 mp, will I see a difference at 8x10 versus a camera that has, say, 15 or 18 or 22 mp? I know I'd see a difference at poster size or bigger, but can the difference be seen at smaller sizes? My opinion is that more resolution makes a better quality image no matter what the size of the print, but the details may not be fully seen. Will a 22mp image look nicer at 8x10 than a 8.5 mp image?

2) Say my camera has a maximum resolution of 18.1 mp, but I choose to shoot at a lower mp setting. Am I losing image quality because of my first question AND because the image mp reduction causes the camera to lose valuable image data? In other words, does making the image mp smaller via the camera setting strip valuable data and metadata from the image, thus making it less "good" to work with, or, do I not suffer any real losses other than making my image smaller?

One of the big differences between digital and film is that with digital you don't see a real difference until you start resampling the image to reach a larger print. With film, you could easily tell even at 4x5 which was taken with the larger format. Not so with digital--until you start upsampling the smaller image, it's very difficult or impossible to tell the difference.

Even when upsampling, a great deal depends on whether the original image captured the required detail for that particular image. Some subjects just don't have or don't depend on as much detail as others, and even lower resolving sensors are capable of capturing all the necessary detail. In that case, it can be upsampled to nearly any size successfully.

For example, nearly any DSLR captures all the detail necessary of in portrait headshot. That's why portrait photographers have been able to take successful headshots even down to 4 megapixels and less.

However, resolution is not usually the only thing that changes with each new model of camera. Noise levels usually improve, processing is usually improved, dynamic range may be increased, et cetera.

Your second question wasn't fully answered by RDKirk although he hints at it. Yes, you do lose image data. But as stated above, it depends.

Isn't format size more important than megapixels when it comes to enlargements? I'm not an expert on the subject, but it seems the less you have to magnify an image from it's original format size, the better the quality.

Racer997 wrote in post #10195863
1) Many of us casually shoot pix for fun. If we get something we really like, we print it 4x6, 5x7 or maybe even 8x10. Okay, so if my camera is has a max resolution of 8.5 mp, will I see a difference at 8x10 versus a camera that has, say, 15 or 18 or 22 mp? I know I'd see a difference at poster size or bigger, but can the difference be seen at smaller sizes? My opinion is that more resolution makes a better quality image no matter what the size of the print, but the details may not be fully seen. Will a 22mp image look nicer at 8x10 than a 8.5 mp image?

Resolution is the resolution of the lens/sensor combination in line pairs / mm. More pixels only contributes a little more resolution – a 20MP camera does not resolve 2x more than a 10MP camera.

The bigger difference is sensor size. If a 35mm sensor is paired with some lens at some f-stop resolves 50 lp/mm, it will show up as ~7 lp/mm on an 8x10 (I believe the goal is usually 6+ lp/mm for resolution-critical work). To do the same lens on an APS-C sensor requires 1.6x more resolution, or 80 lp/mm. In other words, the APS-C camera needs a much better lens or a much higher resolution sensor to yield the same resolution print.

You lose some pixels, which loses some detail. So yes, you lose some resolution. What you need to ask yourself is if that lost detail is important to you. If you only print 4x6's, it probably never would have showed up anyway.

That said, resolution is not always the most important thing. In a landscape, maybe you want to make a huge print and be able to walk up to it and see every little leaf or pebble. In that case, you need a high-resolution print. In a portrait, you only need enough resolution to resolve the hair, so it's not as important.

Also, a lot of people don't care much about resolution, they just want an image that looks "sharp," as in well-defined edges.

to echo what toxic posted...Per DPReview tests, the 3504 horizontal pixel 8MP Canon 30D has horizontal resolution of 1850LPH (lines per picture height). The 5184 horizontal pixel 18MP Canon 7D has 2500LPH. If the simple ratio of horizontal pixels resulted in similar resolution improvement, the 7D would have 2700LPH rather than 2500LPH.

Looking at the issue from a different perspective...using 30D's 1850 lines and the 7D's 2500 lines across an 8x12" print, we have 154 lines per inch vs. 208 lines per inch, or 292 pixels per inch vs. 432 pixels per inch). The 7D has a ppi value which exceeds even the pickiest of applications (400 ppi). But usually 250 dpi is considered the optimum resolution for printing high quality photos, and both cameras exceed that value. Make a print 20% larger than 8x12, and the 30D would be insufficient for maintaining that standard.

at 8x12 I don't think you can tell 4mp from 14mp... but when you go 4 times larger to 16x24 things get different fast.

To reinforce what has been stated before, it really depends on the subject.

A common example is: two similarly sized digital images of a fluffy white cloud versus a closeup of a colorful bird's feathers. You could enlarge the cloud a great deal using up-sampling and it would still look great. However, the bird's feathers would be much more limited in terms of how large you could get them without looking terrible.

Viewing distance matters very much as well. Not many people (besides the ones on this board, haha) are going to view a 20x30 print from one foot away!

Grimes wrote in post #10212865
To reinforce what has been stated before, it really depends on the subject.

A common example is: two similarly sized digital images of a fluffy white cloud versus a closeup of a colorful bird's feathers. You could enlarge the cloud a great deal using up-sampling and it would still look great. However, the bird's feathers would be much more limited in terms of how large you could get them without looking terrible.

Viewing distance matters very much as well. Not many people (besides the ones on this board, haha) are going to view a 20x30 print from one foot away!

Yeah, straight hard-lined objects such as those of a car or a building don't blow up as nicely as softer subjects such as a human face or a cloud.

i mostly shoot jpeg these days, smallest size.
i can blow up 8 mpx 24x36" without a loss in quality, virtually indescernible next to a 21 mpx and nobody ever needs more than that as a print, to be honest

Tadaaa wrote in post #10213627
Yeah, straight hard-lined objects such as those of a car or a building don't blow up as nicely as softer subjects such as a human face or a cloud.

Actually, cars (and other "straight hard-lined objects") usually interpolate fairly well--they don't really have infinitely small detail like landscapes have.

The question is whether the original image was able to resolve the critical detail for that particular subject.

In a human face, the critical detail is facial hair--if the facial hair is sharp, viewers will regard the portrait as sharp. People don't care about detail any smaller than facial hair in a portrait. If the original image resolves the facial hair (and hair is a "straight hard-lined object"), the image can be interpolated successfully to nearly any size.

In an automobile, there are details such as grillwork, insignia, and such. These are fairly large, and if the original image resolves them, it can be interpolated very successfully. Straight, hard lines are easy to interpolate--the software merely adds more straight, hard line.

This is very different from a landscape. Landscapes have infinitely small details, and viewers expect to see these smaller and smaller details resolved as the image gets larger (or they move closer). It's impossible, however to interpolate them; the software can't create a blade of grass or a leaf if the original image recorded only a blur of green.

Karl Johnston wrote in post #10214383
i mostly shoot jpeg these days, smallest size.
i can blow up 8 mpx 24x36" without a loss in quality, virtually indescernible next to a 21 mpx and nobody ever needs more than that as a print, to be honest

Depends on the subject. My 20D images did not resolve facial hair enough to carry a full-length portrait beyond 16x20 before the facial hair was revealed to be just a blurred mass. My 5D2 resolves countable eyelashes on loosely posed full-length group portraits at 24x36.

One thing I haven't seen mentioned yet is cropping - the higher the resolution, the more you can crop (if you need to) and still retain usably high resolution for printing.

I would guess that for certain detailed subjects like birding or macro, resolution matters a great deal. 4mp might capture the bird in flight but 18mp will capture the feather detail as well.

I shoot entirely with a 4mp 1D Classic and in my experience the diagonal lines of things such as a car are more difficult to blow up than softer objects such as a face.