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Film vs. Digital: An Analysis of Chromatic Fringes

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Long story short: The 85 1.2L II was shot wide open in broad day light (to really push it) on a film SLR and a 5D Mk II DSLR to see which medium created images with less purple fringes. Film clearly wins in this sense. The sudden appearance of fringes in overexposed areas (in digital) and not in other areas also suggest this is not lateral chromatic aberration (e.g. see white text on flag vs. SUV)

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Introduction
First, this test does not attempt to compare resolution or the exposure latitude of film and digital. The interest is purely in understanding the appearance (scale) and behaviour of colour fringes (a.k.a. purple fringes) that plague fast lenses, noticeably on digital cameras. Therefore scanning the images any better to improve resolution, shadows, etc. will not help us understand this behaviour any better.

Both the film and the digital versions of the scene were captured few seconds apart. Here are the details:

Cameras: Canon EOS 3 (+ Epson V700 & custom calibrated holders), Canon 5D Mark II

Resolution: 21MP for digital, film scanned @ 54MP then scaled to 21MP. No sharpening applied to either image. 100% crops shown.

Lens: Canon EF 85mm f/1.2L II @ f/1.2 (And no focus changes)

Film/Digital contrast profile: Fuji Velvia RVP 100F, 'Standard' DPP on raw

Sensitivity: ISO100

Shutter speed: 1/3200s

Support: Gitzo GT2541 + Manfrotto 405

Results and Analysis (left: film, right: digital)
Crops 1: The differences here are minimal. It is not certain whether this is because the crops are from the exact center of the image circle (r=0%). Some purple fringing is visible in both.

Crops 2: This set clearly shows the purple "ghost" of the street light in the digital image. The film image barely shows any fringing and its image quality is obviously very high.

Crops 3: These crops are from essentially the same position (r=36% vs. r=35%) on the image circle as the previous (street light) set of crops. However, both shots show some purple fringing on the open car door's glass. The glass here is obviously more reflective than the street light's metal and this could be the reason. So, looking at only these two images, we can see that the film image is not completely fringe-proof but it is more resistant than the digital sensor.

Crops 4: In this set, we hardly see any differences. This was also the case in most parts of the image. I.e. where there were no blown highlights against a dark background, the image quality differences were minimal.

Crops 5: This set shows some odd behaviour. Here, we see no purple fringing on the digital image where we really expect to see some. The pole is dark enough to show the fringes but it does not. Only difference from the previous sets is, here the dark bit (the pole) is in front of the blown highlight.

Crops 6: Another example of the digital image falling apart with fringes. The problem does exist as you go towards the outside of the image circle. Also we don't see the fringes getting on to the dark/black car on the side that is closer to the camera. This is consistent with what we saw in the previous set of crops (with the pole).

Conclusions
Without the need for much explanation, it is obvious that film is much less susceptible to colour/purple fringing than a typical digital camera.

This brings us to the next question: Is this caused by the lens or the imaging medium? From what we have seen, it is easy to think it is the medium that is responsible. But it is difficult to conclude this with full confidence as we have also seen fringes in the film image (crop set 3) but in much lower magnitudes. So from the analysis we have done here, all we can say is that it is possibly a combination of both (the lens and the imaging medium).

As a side note, it is worth mentioning that fringes, aberrations and artifacts cannot be "corrected" although modern camera and popular image editing software claim to do so. Simply put, what is lost is lost. You cannot create information that was never captured. So these "lens correction" software merely hide the appearance of these nasties and in the process, even further resolution and hue losses are possible. Same goes for sensor noise and noise reduction.

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Please take a moment to look at my other articles as well.

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View 17 more comments

  1. Ollievision™ 38 months ago | reply

    Interesting! I'd like to see a 3rd set comprised of the same samples after having been processed with DxO optics pro 7 (on the digital file)

  2. genotypewriter 38 months ago | reply

    Glad you found it interesting, . I'm thinking, even for the film file, there are post-processing ways to enhance the image quality.

  3. Ollievision™ 38 months ago | reply

    I'm sure there will be. I'm surprised to see how good the digital file is compared to the film - I'd much rather have the digital, knowing that DxO can fix the problems you see in one click!
    If you haven't done the free trial then have a go, it's on free download for 30 day trial.

  4. genotypewriter 38 months ago | reply

    When it comes to things that reduce IQ, I take a "prevention" approach rather than a "treat the symptoms" one :)

    You're right, if DXO can hide the fringes very carefully, digital is the way to go when it comes to the two that are compared here because of the higher and cleaner resolution you get from digital. However, with film, we're not limited to small format sizes. And when compared to larger film formats, even the most expensive state-of-the-art digital capture devices (e.g. the best of medium format digital backs) fall behind.

    This is the reason why I've started to shoot film almost exclusively for my photography now. I still use digital for things like infrared and "social" photos where digital is better/easier. Also, even with 35mm film, I find it a lot more exciting to shoot with than digital... for me the latter requires much less effort to get good image quality.

  5. Ollievision™ 38 months ago | reply

    I've always been gob-smacked by what I can see happening in DxO. It turns my EF 15mm fish eye into a lens as sharp as my 35L and 135L. CA and the legendary purple fringing just disappear.

    I think one of the drivers for digital has been weight - that's what decides on my kit. Having to drag 2 bodies and 4-6 lenses around for up to 12 hours a day means that there's no way I could go with medium format!

    I still have my 35mm film kit, but haven't used it for 10 years.

  6. genotypewriter 38 months ago | reply

    : Lately I've been hand-holding a large format field camera:
    www.flickr.com/photos/genotypewriter/6672370943/

    :)

  7. leadingmodels 38 months ago | reply

    OMG. all i see on my home flickr page is this post. LOL.

  8. genotypewriter 38 months ago | reply

    I hate it when that happens... especially when people keep posting "awards" :D

    I just "mute activity" on photos like that.

  9. Back To Nature Photography (b2n) [deleted] 37 months ago | reply

    Great read. Thank you.

  10. genotypewriter 37 months ago | reply

    Glad you liked it, !

  11. Michael_1966 35 months ago | reply

    Perhaps someone with a 5d Mark III could let us know if this is accurate: Taken from the 5D Mark III Canon features list:

    'DIGIC 5+ processor The 5D Mark III contains a single DIGIC 5+ processor. The latest generation of Canon image processing unlocks new capabilities, including:

    Chromatic Aberration Correction The new filtering is implemented in a manner similar to Canon's vignette-reducing Peripheral Illumination Correction: profiles of Canon lens characteristics are loaded into the camera for the glass you use most, and then the correction is turned on in a menu. Chromatic Aberration Correction is applied to both stills and video, and addresses both lateral and axial aberrations.'

  12. genotypewriter 35 months ago | reply

    : This feature has been available for quite a long time now through DPP. It has the best CA and vignette hiding system out there for Canon lenses since it knows exactly how much to remove based on (1) the lens, (2) the position on the frame, (3) focusing distance, (4) focal length (zooms) and (5) aperture. It works with all Canon DSLRs made within the last several years including the 5D II.

    It's interesting that you mention this because, although I don't quite agree that this is CA (since, if it's lens CA it should also be there in the film shot), there's nothing stopping from getting a profile built for the camera to fix it.

    Should be interesting to see. Thanks for your comment.

  13. Michael_1966 35 months ago | reply

    I take your point but the DIGIC 5 processor according to Canon will improve the chromatic aberration. Whether this is accurate or not I don't know.

  14. genotypewriter 35 months ago | reply

    : Adding a sophisticated processor on-board will allow the camera to do certain things that were previously done off-camera (in a powerful computer) but it doesn't mean anything new can be done. At best things might be done faster.

    So, there's nothing new in terms of CA hiding that it can do.

  15. My Sister's Keeper 33 months ago | reply

    A Pro friend who usually shoots a Canon D1 recently had to do a job on 4x5" film (scanned on his Imacon), and says there is no comparison: the film image in clearly sharper even though view camera lenses are lo-res compared to 35mm lenses, although dust and scratches on the film have to be cleaned up. Seen in Film Image Archive Thanks for sharing!

  16. genotypewriter 33 months ago | reply

    : No problem. The larger format lenses having lower resolution is something popularised by people who basically don't know the subject. I say this for two reasons:

    1. In terms of absolute lines/mm, typical LF lenses resolve less detail per unit area than a small format lens, but a LF lens is used on a larger film. To get 36MP from the D800, a lens needs to resolve 204 lines/mm across the frame but to get 36MP from a 4x5" sheet, the LF lens needs to resolve only 56 lines/mm. The LF lens is also able to do this with a larger f-number, something small format lenses can't do easily.

    2. Not all large format lenses are proportionally low in absolute resolution. I have some lenses that are sharp as digital/35mm lenses because they have incorporated special glass that's not used for making lenses anymore. They're not the typical bargain bin LF lenses that the sorts of people who make such claims use to make generalisations. In fact, in my experience, people who generalise lenses based on brand, format, etc. do so after using very few lenses. The truth is there are always exceptions :)

    Thanks for dropping by :)

  17. ~Pixelsmithy 31 months ago | reply

    > Film doesn't have optics built onto it as sensors do. Micro-lenses induce their own
    > problems, such as those seen above.

    DING! DING! DING! DING!

  18. ncay 29 months ago | reply

    Digital capture is convenient for electronics manufacturers (new markets opened), for camera and lens manufacturers (churn out the old bodies and lenses), publishers (photogs now have to do all the pre-press), but not to photographers (expenses of computers, new camera bodies, new lenses, memory cards, long-term storage considerations, backwards compatibility, reduction in aesthetic image qualities, etc, etc, etc). As my father used to say "include me out".

  19. flavio_e 15 months ago | reply


    >"Yes, the reason why the film was scanned at 54MP is because that 's what the native resolution of the scanner gave."

    I'm amazed that nobody has commented on this!!!!
    The Epson V700's *real* resolution doesn't go over 2000dpi for scanning film. 24x36mm = 0.94 * 1.42 inches. This, with 2000dpi of resolution brings up 5.3 megapixels of actual resolution, far, far less than what the film is actually able to hold.

    In short, you can't get 54MP from scanning 35mm film with a V700. In real life you can't get more than actual 6MP of detail from a 35mm frame using a V700. Using a really high-end scanner you can get actual 18MP and even more, depending on the film and on a technique.

    Now, returning to the original topic: The last image surely shows that film is better with regard to purple fringing. But if you could scan the 35mm frame at proper high res, you would see fringing as well. But of course, less pronounced than in the DSLR.

    It is well known by optic technicians that fringing does not evident until the image is sharply resolved...

  20. genotypewriter 15 months ago | reply

    : There's a reason why I started the first sentence talking about how this is not about comparing resolution/clarity/dynamic range, etc. between film and digital... it is one of those things that photographers go off-topic on very easily.

    This experiment doesn't claim any quantitative measurements of fringe sizes between film and digital. For that, several scenes need to be shot with several different lenses, in the least. So that should be your first argument if you think that is what this experiment is about. Not scanning resolution.

    Secondly, you can clearly see details in the film shot that are either/both higher in spatial frequency and lower in modulation than the fringes in the digital image. So, even if the film was examined under a microscope, forget drum scanners, it's not going to go "poof" and suddenly pop-up purple fringes to match (or exceed) the size of the fringes in the digital captures.

    Finally, you're confusing the difference between the concepts "native resolution" and "effective resolution".

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