Explain xkcd: It's 'cause you're dumb.
The lower image has lateral chromatic aberration (seen as a blur and a green edge in areas of contrast.) (from Wikimedia Commons)
Megan's car appears to have combusted at some point while she left it unattended. Suspecting her friends and acquaintances Cueball, Black Hat and Danish of perhaps having something to do with it, she gathers them in front of a couch and draws attention to the fact that something is just a little bit wrong with the two juxtaposed images she shows them. When she asks What is wrong with this picture, they all three take this question literally and start critiquing the picture quality, and not the subject, feigning complete ignorance about the car being on fire. When Megan exasperatedly tells them what is wrong with the picture —that her car is on fire!— they continue to act evasive by telling her that she should buy a better camera.
To some, the title text and the dialogue suggest that they were the ones who collectively set her car on fire, probably in the middle of some nightly exploit. But if you're an engineer or a scientist, you realize that Megan's friends aren't being intentionally evasive, they are just doing exactly what they were told. They patiently and correctly describe what is wrong with the picture. If Megan had wanted to know what was wrong with her car, than she would have asked that. Her friends are just being friendly when they offer to help her recreate the scene so that she can shoot the picture correctly.
As for the particular details of the digital photography terms mentioned:
- White balance: Artificial indoor light is more yellow, outdoor light is more blue. The light colour can also depend on weather or time of day. The human eye is a very good judge of whiteness under a variety of lighting conditions, digital cameras often have difficulty automatically correcting for this which can cause images to look too blue or orange. Professional cameras and image editing software allow you to adjust the white balance manually, which Megan probably has not done.
- Focus is a bit too close: As light passes through a camera lens, it is bent until the rays converge on the film or sensor. If the focus is too close, it implies that point of convergence from the light of the subject is slightly in front of the sensor (i.e. that Megan has accidentally focused on something closer than the car). This will result in near objects being (too) sharp, and the car being slightly blurry.
- Chromatic aberration: This causes coloured artifacts in an image, typically caused by cheap lenses, which do not focus light of different wavelengths (and thus different colours) in the same way. It is usually visible as a blueish or reddish outline around objects.
- Megapixels: This is the number of image sensor elements of digital cameras or the pixels on digital displays. More pixels improve the resolution but can also result in less overall quality for the pictures, due in part to the reduced size of each pixel sensor (because the total sensor size is typically the same for a given class of camera), and because for consumer-targeted products the total engineering budget is limited, so that extra money spent on a high megapixel sensor ends up reducing the money spent on other elements such as the lenses.
While this comic focuses on misunderstandings by people viewing pictures this could be also a reference to the battery fire in a stored, damaged Chevrolet Volt automobile. During a side-impact safety test, which the car passed with a five star rating at Popular Mechanics, its high voltage battery pack was damaged. Part of the test procedure includes rolling the vehicle over after the impact to check for leaking fluids; during the rollover check, the vehicle electronics were flooded with coolant. The damaged vehicle was then put into storage where its high voltage battery remained energized; three weeks later the battery spontaneously caught fire, potentially due to corrosion, and destroyed the car. GM subsequently made design changes to address the causes of the fire.
- [Megan stands in front of a projection of a car, with an audience of 3 people. One of the people is Black Hat, the others are Danish and Cueball.]
- Megan: Attention Please. This is a photo of my car as of two weeks ago.
- [Megan in front of a new projection of the same car engulfed in flames.]
- Megan: And this is my car as I found it this morning. Can anyone tell me what's wrong with this picture?
- [The audience ponders.]
- Cueball: The white balance, for one.
- Danish: Focus is a bit too close.
- Black Hat: The chromatic aberration suggests you bought your camera because it had "The most megapixels".
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- Megan: THE CAR IS ON FIRE!
- Comment from audience: Maybe you should use the insurance money to get a better camera.
- Comment from different person: yeah.
From what I can see of the picture, it is a little over-saturated. The colors look a little too pastelly too. At least decent cameras are cheaper than they used to be. Davidy22[talk] 13:11, 18 February 2013 (UTC)
Does this seem like it might be political commentary? A subtle dig at certain legislative bodies which, when confronted with an urgent problem like "the economy is burning," choose to dicker about the quality of the photograph? Just a thought... 188.8.131.52 05:10, 13 September 2013 (UTC)
I disagree with the apparent majority view that the critics are disingenuous. This might be a satire on camera nerds in particular but also on overspecialized individuals in general. What if the critics are sincere, but just... overfocussed on picture issues, and simply see the world through that lens at all times? Isn't that consistent with the general themes of xkcd? 184.108.40.206 (talk) (please sign your comments with ~~~~)
I feel like the explanation is incomplete, but I don't know what the standard is here. What is "chromatic aberration", "white balance", and what is the significance of "the most megapixels"? 220.127.116.11 04:54, 8 February 2014 (UTC)
- Also. "The title text reveals what she was looking for; one of them really did set her car on fire." How? It seems ambiguous. 18.104.22.168 14:53, 8 February 2014 (UTC)
- 'chromatic aberration' is when different colors in the source are mapped to slightly different locations in the image. A bright white point of light like a star might show up in a photo as a slightly smeared point with a rainbow-like quality in the smearing. Refractive lenses nowadays have coatings to reduce this effect, but they don't eliminate it altogether; there is a similar small effect due to diffraction as well. 'white balance' refers to adjusting the overall color spectrum of the image to compensate for not-perfectly-white source light; imagine if you looked at the same person in 'warm' candlelight versus 'cold, harsh' hospital flourescents. If you are there in person, your eyes quite brilliantly do a little computation to compensate for the difference in source light so that they look human; if you just have a little unbalanced photo in your hand and don't /see/ a roomful of source light for your eye to use as reference background, one of the pictures looks like a zombie and the other might look like your friend is quite flushed. You can use various forms of processing to adjust the 'color temperature' and other details to make the picture look natural, this is white balancing. Note that you might not want to white-balance all photographs, for example you might want to capture the orangey quality of a candlelit scene.
- 'the most megapixels' refers to the size of the camera's images in megapixels. More megapixels is in some sense good, it means the camera is commiting more details to memory; the accusation here is that the photographer bought the camera on the basis of the easily-advertised number of pixels instead of a sensible balance of many important qualities. It is relatively easily to make a camera that has "lots of megapixels" and it looks good in ads, but without a good lens, for example, those extra megapixels are just recording lots and lots of blur. Buying on 'number of megapixels' alone is considered naive, it would be like looking at computer ads and buying a system on "how many gigabytes does it have" without looking at any other quality. 22.214.171.124 (talk) (please sign your comments with ~~~~)
- Thanks for your statements here. This comic is marked as incomplete and a first attempt on the details is done.--Dgbrt (talk) 15:48, 8 February 2014 (UTC)
The title text is written as if from the point of view of somebody who was there watching the presentation, since they're talking about getting the shot, and "we'll set your car on fire AGAIN" implies that they did it the first time. 126.96.36.199 09:51, 25 February 2014 (UTC)
- I am not convinced. "again" might simply mean 'for a second time, regardless of who did it the first time' - that is, the event they are offering to make happen again is 'the car being on fire' not 'us setting the car on fire' 188.8.131.52 (talk) (please sign your comments with ~~~~)
I think the three of them might be genuinely raising the photographic concerns, possibly out of ignorance of the problem of a car being on fire or lack of concern for Megan's (possibly) "trivial matter". This wouldn't be the first time xkcd characters have strange priorities. LockmanCapulet I plead the third! 19:07, 26 March 2014 (UTC)
This seems to be a tribute to Magritte's 'Ceci n'est pas un pipe' (http://en.wikipedia.org/wiki/The_Treachery_of_Images
). It is reminiscent of the unfortunate triumph of appearance over reality (as in TornadoGuard - http://www.explainxkcd.com/wiki/index.php/937:_TornadoGuard