Resolution, megapixels and film

[Christian Thomas]

Hello everyone! I´m new at this forum, glad to be a member , this is a wonderful site with great tutorials, a lot of thanks to the author and to the community... guys you help me a lot, thank you very much!

I have two questions for you, may sound silly but I did a lot of research and finally I don´t think I understand the ¨concept¨ very well. I´m very, very confused!

First question is: How do you compare digital image resolution (MP) with film resolution?

There are some cameras there, that are capables of 16 MP. (Canon 1d Mark IV - if I´m not wrong). How do you compare it´s resolution with an ordinary 35mm film? What about the medium format cameras?

The second question is: Let´s take two full-frame cameras, one of 10 MP for e.g and the second one of 16 MP.
Why the second camera is capable to produce more resolution? It has anything to do with the actual number of physical pixels of the sensor? How many physical pixels a sensor can get, what would be the maximum? More physical pixels means smaller pixels in the same sensor size area? Where do they introduce more pixels if the size of the pixels is also important, how can they fit in the same sensor area ?

Excuse my bad english, I hope you understand.
Thank you !

[carregwen]

The second question is: Let´s take two full-frame cameras, one of 10 MP for e.g and the second one of 16 MP.
Why the second camera is capable to produce more resolution? It has anything to do with the actual number of physical pixels of the sensor? How many physical pixels a sensor can get, what would be the maximum? More physical pixels means smaller pixels in the same sensor size area? Where do they introduce more pixels if the size of the pixels is also important, how can they fit in the same sensor area ?

I'll have a go at the second. Pixels come in different sizes, depending on the size of the sensor and how many pixels the manufacturer want to cram into the sensor to help them sell the camera.

To fit 12MP on a full-frame sensor camera (eg; Canon 5D) you have larger sized pixels which are more efficient at capturing a strong signal, which means less noise. To fit 16MP on the same sensor size means smaller pixels, which may not be as efficient at capturing the light and converting it to an electronic signal. This may cause more noise, but modern processors in some cameras are more efficient than older ones, so it's not just about pixel/sensor ratios.

PS. Manners Rob! Welcome to the forum, Christian (it's been a long day)

[Shadowman]

Hello everyone! I´m new at this forum, glad to be a member , this is a wonderful site with great tutorials, a lot of thanks to the author and to the community... guys you help me a lot, thank you very much!

I have two questions for you, may sound silly but I did a lot of research and finally I don´t think I understand the ¨concept¨ very well. I´m very, very confused!

First question is: How do you compare digital image resolution (MP) with film resolution?

There are some cameras there, that are capables of 16 MP. (Canon 1d Mark IV - if I´m not wrong). How do you compare it´s resolution with an ordinary 35mm film? What about the medium format cameras?

The second question is: Let´s take two full-frame cameras, one of 10 MP for e.g and the second one of 16 MP.
Why the second camera is capable to produce more resolution? It has anything to do with the actual number of physical pixels of the sensor? How many physical pixels a sensor can get, what would be the maximum? More physical pixels means smaller pixels in the same sensor size area? Where do they introduce more pixels if the size of the pixels is also important, how can they fit in the same sensor area ?

Excuse my bad english, I hope you understand.
Thank you !

Hi Christian,

What quality of output (film and digital) have you compared. For film there are a) batch processing/machine prints and b) professional prints. For digital there are a) personal printer inkjet photos, b) machine batch digital c) laser photos d) online labs and e) professional prints. With the correct equipment you can make quality photographs using film or digital cameras. And in my opinion digital photographs have a unique quality that is not found in film based photographs, it is almost too perfect. Film photography has certain flaws, such as grain, that is considered acceptable and sometimes more endearing and would not be accepted for digital photography.

[Christian Thomas]

Thanks everyone, YOU are so FAST ! I really appreciate it!
Now I have a clear image about resolution, pixel size etc...

But, Rob you said ¨but modern processors in some cameras are more efficient than older ones, so it's not just about pixel/sensor ratios.¨, yes is true, but small pixels means less dynamic range too, is that right?

Shadowman: I´ve just found an interesting article about film vs digital regarding their resolution...Now I think I´ve got the idea, my question was a little superficial, you´re right, I think I did not make the comparasing very well.

Thank you very much guys! I´m very greatful!

[Colin Southern]

Hi Christian,

In my opinion, people often get a little too "caught up" in the "megapixel thing". Images from high resolution cameras (eg 18 to 21MP and beyond) give the ability to crop an image quite agressively, but in most cases, the extra detail that they capture simply can't be resolved by the human eye in a typical print (with "typical" being anything from 6 x 4" to 12 x 8").

For really big prints - surprisingly - it still doesn't make a lot of difference in most cases because the bigger the print, the further back people stand to view it - and the further back they stand, the less detail the eye can resolve. I have 22 x 44" canvas prints on my gallery wall that were shot with a 8MP Canon 20D, a 10MP Canon 1D3, and a 21MP Canon 1Ds3 - and you really can't see any difference unless you get up REALLY close (and even then it's not a big difference).

Keep in mind too that print resolution is a square-law dynamic (because images have 2 dimensions) so to double the print resolution of an image taken with an 8MP camera, you'd need a 32MP camera - so in real-world terms, the difference between a 10MP camera and a 18MP camera is really very little.

In terms of Digital -v- film, it's generally regarded that most modern DSLRs have a similar effective resolution. With regards to dynamic range, most cameras have a DR in the region of 11 to 12 stops, but the dynamics are completely the opposite of film; With file you'd expose for the shadows and develop for the highlights whereas with digital you expose for the highlights and then develop (post-process) for the shadows and midtones. Film has excellent highlight tolerance whereas digital has very little.

[Christian Thomas]

Thanks a lot Colin, great answer!

[Steaphany]

Hi Christian,

Welcome to CIC.

I look at resolution from the film perspective, specifically because I started in photography long before the idea of a digital camera ever existed.

When considering resolution with film, it is always defined by the response to "Line Pairs" whose contrast and spacing are well known parameters. A line pair is a bright line alternating with a dark line of equal width. When the resolving power of a film is measured, it is done at two contrast levels because the resolution of film will actually vary as a function of the local contrast. Lets call up a film data sheet to help explain things:

Fujichrome Provia 100F Professional Data Sheet

Open the PDF and go to page 6. There are two sections here that are critical to the film's resolution performance, 17. RESOLVING POWER and 20. MTF CURVE.

The MTF curve is a plot of the flim's ability to resolve distinct line pairs as the width decrease. Even a line pair pattern of pure black and pure white lines will eventually fade to a 50% gray as the film is no longer to resolve the line pairs.

The Resolving Power is more akin to a digital imagers resolution and you can easily convert between the two. As you can see by the film I chosen, when the contrast level is 1000 : 1, the film will be able to resolve 140 line pairs per millimeter and at the opposite extreme of contrast, 1.6 : 1, the film resolves 60 line pairs per millimeter.

As get a sense of these contrasts, here are a couple examples:

High Contrast


Low Contrast

For most photography, we're rarely dealing with such extremes, so lets come up with a single number that would be easy to work with.

Lets calculate the average ( 140 + 60 ) / 2 = 100 Line Pairs / millimeter

For a digital photographer, this isn't the most useful of numbers, so lets convert it to the equivalent of a digital imager. Knowing that the standard 135 film frame ( Standard 35mm film ) is 36mm x 24mm we can do some simple math:

100 lp/mm * 2 * 36mm = 7,200 "Pixels"

100 lp/mm * 2 * 24mm = 4,800 "Pixels"

Remember the multiply by 2 is to turn line pairs into the individual resolvable pixels. I put the resulting Pixels in quotes since film does not have individual pixels but these would be the minimally resolvable areas that we can term as a pixel.

Lets multiply these numbers to get:

7,200 "Pixels" * 4,800 "Pixels" = 34.56 MP

Ever see any dSLRs claiming anything close to a full frame 34.56MP imager ?

So, how would a dSLR compare ? Well, my dSLR will keep life easy for us, a Sigma SD14. The SD14's Foveon imager stacks pixels within the vertical bulk of the Silicon chip, very similar to the layers of a color film emulsion. ( I'll explain why Bayer imagers would be a head ache in a bit ) I know that Sigma marketed the SD14 as a 14MP dSLR, but we know from the film example that the emulsion layers aren't counted seperately, so in real life, the Sigma SD14 is a 4.7MP with a native resolution of 2652 x 1768 pixels. To understand the numbers we also need to know the SD14's frame size of 20.7mm x 13.8mm. Lets do the simple math to turn this into a film style resolution number:

2652 Pixels / 20.7mm / 2 = 64.06 Line Pairs / mm

So, where the 34.56 MP film value is significantly higher than SD14's 4.7MP, the fact that the SD14's 64 lp/mm is not all that below the film's 100 lp/mm means the resulting image quality is fairly close.

Now for the Bayer Horrors !

A camera employing a Bayer masked imager is a very different critter than the Sigma/Foveon or film. For every Green sensing pixel, there is a neighboring location where the Green value is guessed at. Red and Blue are worse in that for every sensed pixel, there are three neighboring pixels that need to be guessed at. This is what is referred to as interpolation - A fancy word describing very sophisticated mathematical processe to recover missing data.

This means that for every image file pixel, one channel is real and the other two have been guessed.

To complicate matters further, Bayer masked imager based cameras employ a soft focus filter to eliminate the phenomenon of Moiré patterns caused when details of the the image falling on the imager becomes close to the spacing of the photosites. Camera manufacturers don't call it a soft focus filter, since they are trying to get prospective buyers into thinking their camera will yield the sharpest image, so this is termed an Anti-aliasing filter. Ether way, no matter how good the optics are or the over all quality of the imager and mathematics behind the interpolation, you still have a soft focus filter in the light path.

As you can see by my examples, mathematically equivalencing a Bayer masked imager to film resolution is not a simple task, but feel free to approximate by using the prior formula that I shown for the SD14. The results should be close enough.

See Hot Rod (High Resolution) Your Camera For Maximum Resolution! for more details regarding the Anti-aliasing filter.