What Is Resolution?



Ok, so most people equate resolution to the number of Megapixels, especially when comparing digital camera qualities, but this is not entirely accurate. Image resolution is basically the amount of detail an image can show. It is the quantification of the degree to which two lines next to each other can be visibly resolved, or discerned from each other. If a camera, film or lens can produce an image where you can see clearly defined edges of the smallest details, the resolution is said to be high.

So, Megapixels then become a kind of unit of measuring resolution in digital images. Resolution is determined by the size of pixels present in the image, and the more the pixels, the smaller they are. However, naturally, this has to take the size of the area in question as well. Plus, there are other considerations as well, such as the image processing algorithms and interpolation of pixels, which we will discuss further shortly.



Film resolution is measured in lines per millimeter, and these lines comprise pairs of a dark and a light line, also known as line pairs per millimeter. Since film records details naturally, there are no algorithms and computer interpretations to mess things up and the details you see are extra-ordinary, especially with medium and large format sheet film.



Sharpness and Detail



Film naturally records the finest of details in a given scenario, which means you get coarser textures as well as finer ones. Digital sensors are less responsive to fine details, however, but are extra sensitive to the medium level details that they can see. These are exaggerated by boosting the contrast which results in a highly sharpened image which is intended to make up for the lacking in detail and to give a false sense of sharpness in the resulting image. This is one of the reasons film images look so much better to the eye; the natural way it records the coarser details rather than heightened contrast is how our eyes naturally respond to visual stimuli as well.



RGB Resolution



Except for Foveon sensors, all digital sensors are black and white, covered with red green and blue dots. This means that each pixel does not have complete R, G, and B information, with each color only covering one-third of the sensor. This translates into one-thirds of the resolution for each color, which means that the megapixels states by camera manufacturers for their products are grossly exaggerated.



Since each pixel only has one-third the color data needed to be resolved, digital cameras use something called the Bayer Interpolation firmware which helps them interpolate, or guess at the values in between the pixel locations of each color to come up with brightness value for any given color. So, if a camera states it can resolve at 25 MP, it can usually only resolve at half, or sometimes even less than that, and the rest is a result of interpolation algorithms and smoothing over.



On the other hand, in film you have full R, G and B resolution at every point and get endless amounts of color information and details throughout the image. So you get the same resolution for different colors being recorded, and the resolution you stated is the resolution you get in the results.



The Real Resolution of Film



So, when we take all this into mind, what is the real resolution of film? It captures way more detail than any digital camera can, but this detail cannot be conceived in any measure that can be easily compared with digital. When we zoom into a quality shot taken with film and digital both, we can see the differences clearly; with film you get the finer details of textures that digital will smooth into oblivion while maintaining sharp edges to make us think the image is still sharp.







However, we still want to know what the resolution of film is in terms that we can relate to, such as mega pixels. Kenny Rockwell gives us a nice, simplified formula to do this which is quite helpful. Most films have an average resolution of 150 line pairs per millimeter and we’ll use this as an example even though different films may differ.



Now, 150 pairs mean 300 lines, or 300 pixels per millimeter in any one direction. When we consider the whole area of the film, we get 300x300 which is 90,000 pixels, or 0.09 megapixels per square millimeter.



Now, this will translate very differently for different sizes of film. When we look at 35 mm film, it has a surface of 35 x 24 = 864 sq mm. This means that a piece of 35 mm film has 0.09 x 864 megapixels, which is almost 78 megapixels. And this is not the digital camera pixel count which is really only half of that, this is film where each pixel would have full RGB rendition.



A digital camera would have to be 156 megapixels to give you the same kind of detail as 35mm film.



And of course, this is just 35 mm; with medium and large format you get even more detail, and the larger you keep going the possibilities keep skyrocketing. With medium format 6x6 film you get 56 x 56 = 3,136 sq mm, which is 282 megapixel.



Large format 4x5” would be 95 x 120 mm, which is 11,400 sq mm, and 1026 megapixel, with full RGB data at each pixel. With 8x10 sheets or 203 x 254 mm you have 51,562 sq mm and 4640 megapixel, which is insane.



Output Method



While film itself might have a high resolution and an ability to capture endless detail, what we end up seeing is limited to the quality of the output method. Recently most people have started scanning their film digitally, and the scanner will only be able to resolve the details up to its DPI or dots per inch rating. The film may have a lot more detail to show, but this cannot be resolved by the scanner.



That being said, the scanners can resolve the fill RGB information available for each pixel and can resolve as well as the film can up to the finest detail that they can respond to. A lot of people tend to compare digital scans to digital cameras when comparing resolution, rather than comparing film, which results in a declaration that digital has caught up, or that digital is better. The quality of the scans will no doubt depend on the quality and abilities of the scanner, and if outdated low quality scanners are used, the results will not be that great, just as a low quality monitor will display you 25 MP camera results in a poor light.

Some other factors to consider



Output methods are not the only thing that affects the quality we see and get. Lenses have their own lines per millimeter resolution ratings and play a huge role in whether or not you can tap into the resolution potential of the camera. Another factor to consider is your own ability. Your skills as a photographer need to be highly refined in order to capture the amount of detail possible with film, and should also have the skills and resources to make quality prints/ scans from these exposures. If you’re making comparisons between film and digital, these factors need to be taken into account, and your equipment, subject matter, exposure settings and other factors influencing quality should all be controlled so that the details and resolution can be truly compared.



What we can take away from this is that the real resolution of film is endless. We can try to quantify it, but the amount of detail it can capture can only be seen through the various methods we use for output, that is scans and prints. With the advancement of scanners we have seen that film resolution just keeps better and better, with the scanner unlocking more of the recorded detail. The possibilities are endless, and while we talked about how the resolution doesn’t make a great picture, it is kind of helps to push our limits and see how much better it can get.



Interested in shooting film? Be sure to check out our The Beginner’s Guide To Film Photography!

