Sunday, September 14, 2014

Games I own and never finished

Many people will play several video games intermittently, and may well leave some of them unfinished (or in a perpetual state of "I'll finish it some day.") I don't do that. When I start a game, I generally play it through before going to another game (at least on the same system.) I don't like leaving games unfinished. (Also, while I don't outright rush through games, I don't really willingly prolong them for as long as possible either.) Even if a game is bad or boring, I really hate leaving it unfinished, so I generally play it through before uninstalling it and going to the next game.

Thus it's quite rare that I leave a game unfinished. There usually has to be a reason for it. Many times it's simply because the game outright bores me out of my skull, but that's not always the reason. Sometimes it isn't even that the game is bad.

Just for the fun of it, I'll list here games I have left unfinished (and will probably never finish), and ponder a bit about the reason. No particular order. (Also note that this list is incomplete, and I might update it from time to time with new entries at the end.)

Assassin's Creed (PC)

The reason I stopped playing this was not because it was a bad game, but because my PC of the time had hard time rendering it at a decent quality, and at some point it kept constantly crashing. (My Windows XP system of the time was overall so corrupted that about 50% of all games crashed more or less frequently, so it wasn't a surprise. In this particular case, however, there was a point in the game where it was outright impossible to continue because it kept crashing every few minutes.)

I have since bought and played through all the three games of AC2, as well as AC3 and AC4, and somehow I have never got around to finishing AC1. Somehow it just doesn't feel all that interesting anymore.

Naruto Shippuuden: Ultimate Ninja Storm Generations (Xbox 360)

The reason why I bought this game was because I had previously bought and played through Naruto: Rise of a Ninja for the same console. While it wasn't necessarily the best game I have ever played in my life, I enjoyed it. Thus when I looked at what kind of sequels there might be in the same franchise, I found the Ultimate Ninja Storm franchise in Wikipedia.

Since there are many games under that franchise, it wasn't easy to choose, so I picked one that looked interesting from its description, and was relatively cheap, so I bought Generations.

This game probably set a personal record of how little I played it before I stopped.

You see, Rise of a Ninja was an open-sandbox free-roaming game, where the fighting was done in "Tekken-style". This was a marvelous idea, in my opinion, and I really liked that. I have always wondered why they don't incorporate "Tekken-style" fighting as a mechanic in RPG's or other such free-roaming games, and Rise of a Ninja is the closest to that I have encountered so far. (It's not an RPG per se, but pretty close.) Thus I expected Generations to be like that, just upgraded with more mechanics and more quests.

The main menu looked promising because it had a real-time 3D-rendered version of the Leaf Village, exactly like the free-roaming portions in Rise of a Ninja (or at the very least it looks like it's real-time rendered), so it gave the impression that it's exactly like it in terms of game mechanics.

When I started to play the game, there was a cutscene, and then a fight. Then another cutscene, and another fight. At this point I was simply wondering if this is some kind of tutorial to teach you the basics of fighting. Then there was yet another cutscene and another fight... I think that after about the fourth cutscene followed by a fight I got so suspicious that I had to look it up.

It turned out that Generations is not an open-sandbox game at all. It's a pure Tekken-style fighting game, period. No free roaming, just custcenes and fights. It turned out that I had read the description of the game (eg. at Wikipedia) too carelessly, and missed this.

I don't dig that kind of game at all; not as a single-player game. It was also such a huge disappointment that I just stopped playing it. What a waste of money.

Games with checkpoints too far apart

There are some games where there are checkpoints (most of them are automatic, in a few of them you have to save manually), so that if you die, you start from the last checkpoint. In most games this mechanic works well, and has been well designed. In other words, the checkpoints are in convenient and rational locations, and it seldom feels that you have to do too much repetition in difficult parts.

In a few games, however, they screwed up the placement of checkpoints completely. In some of them so badly that I had to simply stop playing the game out of sheer frustration. Examples include:
  • Resident Evil 5 (Xbox 360): This is an ok game, and I could play it almost to the end. However, somewhere by the end parts of the game I stumbled across this very problem: A very long stretch requiring several minutes to play through, after which an extremely difficult enemy appears. This enemy kills you in one shot if it catches you, and is extremely difficult to kill. Ok, so at one point, after like a dozen or so attempts, I manage to kill it and continue. I go to a room with a lever on it, I pull it, and there's no other way than to go back. When I go back, another enemy of the same type appears and kills me. And you guessed it: No checkpoint in between these two enemies. I had to repeat everything all over again. I gave up.
  • Patapon 3 (PSP): There's a level where you have to play (once again) an extremely long and repetitive stretch, until you reach a point with a death trap which is extremely difficult to avoid. If you die there, you go all the way back to the beginning of the level and have to do it all over, again and again and again. There is no checkpoint right before the death trap. You get to try to pass the death trap each 10 minutes or so (after each time repeating the exact same things over and over). This would be bad even if there were some kind of trick you can use to bypass the trap or pass it safely, but no, there isn't one. It really is as difficult as it seems; there's no trick to pass it easily. And it's basically instant-kill. And if you do manage to get past the trap, with half of your team dead and the other half almost-dead, can you guess what comes after it? The end of the level (and thus a savepoint) perhaps? No, more difficult enemies that will wipe your weakened party out with ease. And no checkpoint, so when you die, back to the beginning of the level. Again, I just gave up.
  • Condemned 2 (Xbox 360): The game is significantly more boring (and extremely dark; you can't see anything at times) than its predecessor, but it was barely playable. Up until some time in the earlier parts of the game when I stumbled across this problem: After a checkpoint there was a very long stretch of a level that took several minutes to play through, after which came a very difficult battle where you are very underhanded and with no obvious solution or escape (if there is a way to escape the battle, it's not obvious at all, and it's difficult to find a way out when enemies are constantly attacking you). I played that long stretch about a dozen times before giving up on the game completely. What a waste of money.
  • Aquaria (PC): Same story with the final boss (or I think it's the final boss): Extremely long and repetitive long stretch after the checkpoint, followed by an extremely difficult fight which you will most probably lose, and rinse and repeat. And again this: After about a dozen times trying it to no avail, I gave up.
  • Dead Rising 2 (Xbox 360): This is a bit different because it's more of an open sandbox game, and savepoints are scattered at fixed locations where you can go almost whenever you want. However, they are really far apart from each other, and often very difficult to get to. This can be especially frustrating when you have one life bar left, no food anywhere in sight, and you are surrounded by a horde of zombies right after a long and difficult battle that you just barely survived. No checkpoints, of course. If you don't manage to get to the nearest save point, you'll have to do the long and difficult fight all over again (not to talk about getting to the fight in the first place could take a long time from the nearest save point). I gave up in frustration with this one as well, somewhere by the end parts of the game. It was just too annoying.

Driver 3 (PC)

Long time ago I bought Driver for the PC, and it was really fun (regardless of its limitations due to it being designed for very antiquated PC's and consoles.) Some years later I bought Driver 3, expecting it to be at least as good.

The game (originally developed for the PS2 and the Xbox) is a complete disaster of a port for the PC. It does not support a wheel controller properly (even though the first Driver did), and the gamepad controls are just horrible (eg. turning the camera is extremely slow, and there's no way to set the sensitivity anywhere).

More damningly, though, the car is basically impossible to drive, to the point of the game being unplayable. The car is way too bouncy, flipping even from the slightest of bumps, the drifting is extremely hard to control (you extremely easily over or underdrift, and there's no way to correct it after the drift starts), and colliding with basically anything either makes your car to stop completely, or turn 180 degrees. In both cases you effectively lose because it takes way too much time to resume the chase of the other car. (And if you think "well, drive more slowly", it's not possible. The other car drives so fast that you can barely keep up with it at full speed. Any slower and it escapes.)

Oh, and did I mention that the car to be chased takes a random route through the city each time? And that the other cars are spawned at random? In other words, you can't even memorize the chase with practice because it's different each time.

Oh, and did I mention that this is the very first level? Not a final boss battle or anything. The very first introductory level, where you chase a bad guy for the first time.

To my estimation I tried to pass this first level at the very least 50 times, probably a lot more (and this is not an exaggeration.) 90% of the time I lost on the first couple corners. In no attempt did I get even near the half-way point of the chase. I gave up on the game for the simple reason that I could pass even the first level. (And note that I had eg. played the first Driver game to completion on its hardest difficulty setting, so it's not really a question of skill.)

(Note that this might be a problem with the PC port of the game. I have watched let's play videos of the original PS2 version, and it looks very different. The car is not even nearly as bouncy, does not turn 180 degrees or on its roof even nearly as easily, the drifting looks a lot easier, and there's significantly less traffic.)

Resident Evil 4 (PC)

I recently bought the PC port of Resident Evil 4 because it has extremely good reviews and critical acclaim. This game rivals Naruto Shippuuden: Ultimate Ninja Storm Generations in how long it took for me to stop playing it. (I don't know how much time exactly I played the Naruto game. Steam tells me that I played Resident Evil 4 for 33 minutes. I don't know which game I played the shortest. They are close.)

This is not a porting disaster. The game, including its controls, are exactly like on the PS2. And they are absolutely, totally, unyieldingly horrible.

Rather than use normal controls, which have existed for almost as long as DualShock-style gamepads have existed (in other words, from at least 2001, or even earlier; Resident Evil 4 was published in 2005), they instead decided to use "tank controls". In other words, moving the left thumbstick forward and backward moves the character forward and backward as normal, but moving it left and right does not. Instead they turn the character left and right (something that's usually done with the right thumbstick in the vast majority of other games, even at the time). In other words, you can't move sideways (with respect to the direction you are looking). The right thumbstick looks around... a bit; it doesn't turn the character in any way. There is no way to move sideways at all.

That's not the most damning thing about the controls, however (after all, with a bit of practice you kind of get used to it). Not being able to move sideways is a big hindrance in fights, but you kind of get used to it. The most damning, however, is that the only way you can shoot is to press the aim button (left trigger by default), and while aiming you are locked in place. You can't move. In other words, if you want to shoot, you can't move, and even when you move you can't move sideways. In other words, in combat you have extremely little control over your movement (because moving just forward or backward makes it very difficult to do anything. If your back is towards a wall, good luck. You're screwed. You can't move sideways to avoid the enemies.)

On top of it, even with the left thumbstick the character turns slooooooowly.

All this makes the game artificially difficult to play. The difficulty doesn't come from gameplay, but from an awful limited control scheme. You basically can't move in battles in any normal or rational manner, and if you can't shoot all the enemies dead fast enough, you are dead. This got so frustrating so fast that I just stopped playing.

Another waste of money.

Bastion (PC/Xbox360)

This is a really, really strange case. Bastion has sold tons of copies and has received critical acclaim from both reviewers and gamers alike. Personally I also like smallish indie games that try something different and innovative (such as Limbo, Braid and World of Goo).

A few years ago I tried the demo version of Bastion on the Xbox 360 because it had got such good reviews. It left me ambivalent... so ambivalent that I didn't buy it back then.

Recently it was on sale on Steam, so I bought it. Perhaps I just didn't give it a fair enough chance?

So I played, and advanced several stages... most of the time struggling with motivating myself to continue to play. I really can't explain why, but I just find Bastion boring, and even somewhat frustrating. Keeping playing feels more like a chore than anything else. I fully understand that people like the game, and as said, I don't really understand why I don't. I love games like Limbo and Braid, and this seems somewhat on par with those... yet it's not, somehow.

I have noticed a good rule-of-thumb with both movies and games: If the movie or game doesn't seem very interesting in its first 15 minutes (or maybe 30 minutes in the case of games with long intros), it's highly unlikely that it will become interesting later. There are exceptions, of course, but they are exceedingly rare. And Bastion was not such an exception.

Steam shows me that I struggled with the game for almost exactly 2 hours before stopping. I just couldn't motivate myself to continue, even though I can't really put my finger on the exact reason.

Might & Magic: Heroes VI, King's Bounty: Crossworlds (PC)

I'm putting these two games under the same section because of how similar they are in gameplay. And also because the reason I stopped playing them is very similar.

The main reason why I stopped playing both games was because of how unyieldingly hard they are. I don't oppose hard games per se, but there's a certain type of difficulty that I find boring.

The thing about both games is that they seem at first very casual and fun, but as you advance a bit in the games, you find out that in fact they are really hard, and not for casual gamers at all.

M&M: Heroes VI is, at its core, an optimization game, but this doesn't become apparent until quite late in the first actual mission (after the tutorial mission), which is rather lengthy. In other words, you have a limited amount of resources (mostly soldiers) available to you, and you have to really optimize their usage during the entire campaign (and even from the previous campaign, as the resources carry over) if you want to be able to complete it. The resources are renewable, but they renew very slowly; way too slowly to be of much help. And you can't simply wait out for them to renew, because the enemy will actively attack you when enough time passes.

If you didn't optimize the use of resources during the entire campaign (and why would you; the game gives you no hint that this is a necessity), it will become basically impossible to complete the campaign. Enemies become way too hard by the end because you wasted your limited resources earlier in the campaign.

I understand the core idea of the game: You play the campaign over and over, from the beginning, until you succeed in finding an optimization strategy that works. In other words, you are kind of supposed to play campaigns over and over until you succeed in finishing them (unless you are already so savvy of the game genre that you already know what to do). The reward comes when you finally succeed.

The thing is, I don't find this type of game (ie. one where you have to play the same levels/campaigns over and over until you succeed) very enticing, with very few exceptions (if any).

King's Bounty: Crossworlds, besides being almost identical in its fighting system, is also similar in terms of difficulty and resource management. Curiously, the difference here is that what's limited is not your own resources, but the amount of enemies/opponents.

That might sound a bit strange at first, but the thing is that you gain experience points and other stuff from enemies, and you need to level up in order to be able to defeat more difficult enemies. In the vast majority of RPG games you simply level-grind to achieve this. However, level-grinding is not possible in this game because enemies are "single-use": There's a fixed number of enemies on the map, and once you have defeated an enemy, it never respawns. This means, basically, that you can only get a limited amount of exp and other stuff. Level-grinding is not possible.

This would be completely ok, if it weren't for the unyielding difficulty. The strength of enemies jumps very quickly to almost impossible levels as you advance in the game. The game becomes basically a hunt for weaker enemies that you can defeat to level up, and they become scarcer and scarcer as you defeat them.

I suppose this is also a kind of optimization game, where you have to gain exp and other stuff in the most optimal way if you want to advance beyond a certain point. The problem is that if you didn't find the optimal strategy, you are pretty much stuck behind a wall of enemies that are way too strong, and no way of getting stronger yourself.

Watch Dogs (PC)

Most of the game was ok. Then the final boss (or at least one of the bosses near the end of the game; I don't know because I never finished the game) is amazingly frustratingly difficult. After having replayed that long boss fight something like 50 times, I finally succeed in killing it... only to be killed myself by that other almost invulnerable guy. I quit in frustration.

(Sure, that boss fight might be easier with practice and if you know what you are doing, but I consider it bad design if a game is frustratingly and infuriatingly difficult for no reason, and especially when it feels unfair in the fact that if you succeed in a very difficult sub-task, you are not yet done and could well be immediately killed by something else... and without any kind of checkpoint in between, forcing you to repeat that long fight in its entirety once again.)

Valkyria Chronicles (PC)

This is somewhat similar to Bastion in that this game has very good reviews (both by critics and players), and it's not a bad game in any way... yet I find it a real chore to try to play through, and it's difficult to put my finger on why exactly.

The tactical combat system is quite good... yet somehow I get "fatigued" after one single mission; so much that I get a strong urge to just stop playing. It's strange, really; the combat missions are somewhat fun to play, but somehow I get tired of them quite quickly. It's hard to explain. Playing one mission through does not give the urge to keep playing further missions, but the opposite, even though I didn't actually hate playing it. It's somewhat enjoyable, but not very addictive.

On top of that, it really doesn't help that there's too much non-interactive visual novel stuff in between missions. Some storytelling is always good, of course, but there becomes a point where it's a bit too much.

And it's not like I hate tactical RPG's. I just love games like the Disgaea franchise, Final Fantasy Tactics, Tactics Ogre and Jeanne D'Arc. (Valkyria Chronicles is not exactly this kind of tactical RPG because it's not grid-based, instead having completely free movement, but the basic idea of the combat system is similar.)

The Witcher and The Witcher 2

I bought The Witcher 2 years ago, and played it for something like 12 hours. The game is technically superbly made, and has clearly a lot of production values. However, I found it slow-paced, tedious and, worst of all, too difficult in the wrong sense. (High difficulty in itself is not a reason to not to play a game, if the difficult gameplay is well designed and engaging. But this just isn't like that. It's frustratingly difficult, which is really a showstopper. Difficulty that's challenging and engaging is good, difficulty that's frustrating is not.)

Somehow the story is vague and advances slowly, it's hard to explain why. It didn't feel very interesting. Combat was not something I looked forward to, but on the contrary dreaded (because it was more frustrating than enjoyable). And it seems to me that this is one of those RPG's that are really, really long, because even after the 12 hours I think I was still quite at the beginning parts of the game. (I don't mind long games at all, when they are well made and interesting. For example Steam tells me that I played Fallout: New Vegas for 60 hours and Skyrim for over 100 hours, which is a lot. I don't know how accurate those numbers are, but they are approximately ok at least.)

I recently tried playing it again, but this time couldn't play for even 2 hours before I became completely unmotivated.

A bit ago, for some reason I don't even understand anymore, I bought the first game of the series. It has excellent user reviews, the critical reception of the game was good, and the screenshots didn't look too bad. Steam tells me I played the game for 2 hours before stopping.

While the second game is technically excellent, this game is technically schizophrenic. It was published in 2007, and some of the graphics look ok for that time (even though there are many games from that year that look significantly better), while other graphics look like they are from 2000; some of it is really ugly to look at. Character animations are just horrible, like they are from some cheap game from 1995. The combat system is hideous (and one of the biggest complaints about the game); it's not unsurpassable, but annoying nevertheless. The story... well, what story? Granted, it's impossible to say anything about the story from playing for 2 hours (which means the tutorial levels and a bit of the beginning of the game proper), but remember what I wrote earlier: If a game doesn't interest me in the first half hour (or even 2 hours in this case, if I'm willing to give it the benefit of the doubt), it's unlikely to interest me later either.

Bloodborne

If you don't know what kind of game Bloodborne is, you might have heard of Dark Souls, which this is kind of a "spiritual successor". It's one of those really, really hard modern "rogue-like" games. The high difficulty is, in fact, one of the basic ideas of the game, as it's rewarding when you overcome difficult parts. It's the kind of game where the player himself becomes better in addition to (or even moreso than) the playable character, and you learning the gameplay contributes as much or even more to beating difficult enemies as the leveling-up of the character.

Bloodborne and the Dark Souls series succeed in making extremely difficult gameplay interesting. However (and that's quite a big "however"), there's a really fine line between being highly challenging and being tedious to play. If the game becomes too repetitive, when advancing becomes too much of doing the same thing over and over, the game may slip into the tedious side of the spectrum, and become annoying rather than rewarding to play.

And that's exactly the reason why I just stopped playing Bloodborne. I don't mind the high difficult of the "Souls" games; that's just fine. I don't even mind having to level-grind, or to try the same boss dozens of times, if the fighting mechanic is interesting, and winning feels rewarding. However, I do mind if it requires a half hour or more of other gameplay before you can attempt the boss again. That's when the game swings from challenging to tedious really fast.

There's this one boss (by, perhaps, one quarter of the game, or such) that's pretty much hopeless to try unless you have a full stock of health potions ("blood vials") and antidote pills. You can try it, of course, and perhaps a really, really experienced hardcore player could beat it without the need for any, but for anything less than that (like me) it's pretty much hopeless (and a waste of time to even try).

Fine, just restock and try again? Except that it requires a lot of time and gameplay to restock. The only way to buy or get these items is to kill enemies. Lots and lots of them. Sometimes they drop a blood vial, and while restocking that way is possible, it takes a very long time because it happens so relatively rarely. The antidote pills are, however, the bigger problem. Again, enemies sometimes drop them, but significantly more rarely, and it would take an enormous amount of time to restock that way.

Killing enemies, however, gives you "blood echoes", which is kind of currency. You can buy items with them. However, to fully restock this way you have to kill so many enemies that it takes at the very least half an hour of gameplay, possibly more.

This means, in practice, and as I mentioned, that it takes at least a half an hour of gameplay (in the same places as you have already been a myriad times) if you want to try that boss again. And fighting it will require you to consume those vials and pills like mad, so most (if not all) of them will be gone before you die, again.

And the thing is, you won't level-up while doing this. That's because the exact same "blood echoes" currency is used to level up. So it's an either-or situation: Either you restock, or you level up. You can't do both (unless you are willing to spend a long, long time to do so). So if you want to try this boss again and again, you won't be leveling up while restocking, and thus you won't be getting stronger. (At this stage leveling up even by one level requires killing so many enemies that it takes like an hour of gameplay.)

I wouldn't have minded all that much if I had to try this boss a hundred times before beating it. However, having to go through the same repetitive motions for at least a half an hour each time was too much. It's way, way too tedious. I gave up.

Edit: I gave the game a second chance, just to see if I could pass that boss after taking a break. I spent something like 3 hours getting a full stock of blood vials and antidotes, and on top of that I level-grinded one additional level (which at this point takes quite a lot of time), and I got the strongest weapon in the game and took the time to upgrade it. I looked up strategy guides for that boss. I then went to said boss, and tried to beat it as carefully as I possibly could. All 10 antidotes, gone. All 20 blood vials, gone. Boss has still about one third life left. I die. I give up. I'm not going to spend another hour restocking just to try one more time and die again. It's not the difficulty of the boss; it's the insane amount of repetitive and tedious grinding needed each time you want to try it. It's just too much.

Thursday, September 11, 2014

Why net neutrality is crucial

"Net neutrality" means that service providers and other companies who are in the business of transferring internet traffic from one place to another, have a completely neutral stance on what is transferred from where and to where. They do not give special treatment to data coming from or going to specific internet domains. They just transmit data from place A to place B, and that's it. Everybody is treated equally.

Why is net neutrality important for end users? There are many reasons, but one of the most important ones is that it keeps prices down. In other words, you, as an end user, end up paying less for online services, such as for example online video rental services.

Why? Because net neutrality ensures healthy competition between companies. All companies are on equal footing when it comes to online services. Companies compete with each other with amount and quality of content, rather than the amount of lag that you experience when you access their online services. And as we all know, healthy competition in the market drives prices down: In order to succeed you need to sell your product cheaper, or else customers are simply going to go to your competitor.

Some big corporations do not like this, and thus are pushing for getting special treatment from internet service providers. In other words, they want to pay money to ISP's so that their services will be accessible at normal speed, while everything else is accessible at only a fraction of that speed.

In the end this would kill smaller competitors who can't afford to pay this "protection money". For example some smaller online video rental services may find themselves in a situation where their customers can't actually watch their videos, or the videos are of much poorer quality, because the connection is too slow.

And what happens when smaller competitors have been driven off the market? Prices will raise. That's the inevitable consequence of achieving a monopoly (or a cartel) status on the market. In other words, you will end up paying more for the same service than now.

Thursday, September 4, 2014

Buying an unused product from a friend

How many times has this happened to you: You have bought a product, but it turns out you have no use for it after all. Thus you would like to sell it to a friend or acquaintance. The product is completely unused, unopened in its original package, and exactly like new, and you have the receipt and possible warranty papers. Yet no acquaintance is willing to pay the full original price for it. They always want a significant price reduction.

But why?

This seems to be a very strange instinct that 99% of people have, and I suspect that in one form or another it's something that corporations have in one way or another succeeded in implanting into people's minds. Or, at the very least, are very happy about.

For some reason this instinct is so strong, that most people would prefer to buy the product directly from the shop than from a friend, unless they get a price reduction, even though this makes absolutely no logical sense.

It doesn't matter if the product is completely unused, even unopened, in its original package, and exactly like it is when you buy it in the shop, and you have the receipt and any possible warranty papers that might have come with the product. They still want the price reduction, or they prefer to buy it from the shop rather than from you.

There is no excuse that makes sense. If the product turns out to be defective, they can simply go to the shop for a replacement, given that they have the original receipt/warranty. There is not even any kind of theoretical loss that they could suffer. And yet, most people would never pay the original price, if it's not directly to the shop.

It makes no sense.

Tuesday, September 2, 2014

Gamma correction

In imaging, especially in computer imaging, gamma correction is something that both gets largely ignored, and can be a real nightmare at the same time.

In order to fully understand gamma correction, we need to understand how human vision, as well as display devices, work.

Our perception of brightness is dependent on the amount of energy carried by light. In other words, the more energetic the light is, the brighter it looks.

However, the relationship is not linear. One could hastily think that if we double the amount of energy, it will look twice as bright. However, the human eye doesn't work that way. Doubling the amount of energy does not double the perceived brightness. The actual function is quite complex. Thus we have two different concepts:
  1. The absolute amount of energy carried by light. The technical term for this is radiant flux.
  2. The perceived brightness of the light. The technical term for this is luminous flux. (Yes, it's confusing.)
As said, the relationship between the two is not linear, and in fact is quite complex. It can be, however, approximated with a logarithmic curve. (Although, complicating things even further, the curve depends also on the wavelength of the light, as the eye perceives different wavelengths in different manners.)

Normally we don't need to worry about this difference. However, there are some applications, such as computer 3D rendering, where, if the application wants to be as physically accurate as possible, the distinction needs to be made. For instance, the amount of light reflected by a surface is a function of the cosine of the angle between the incoming light and the normal vector of the surface. However, it's a function of the radiant flux, not the luminous flux, which is the perceived brightness of light. (For example, at 60 degrees the amount of reflected light is half of the amount that's reflected at 0 degrees. Half of the radiant flux that is, not half of the perceived brightness.)

Another example is image dithering: If you want to reduce the colors of an image and use dithering, you need to be aware of gamma correction if you want to retain the perceived brightness of the result. (The reason for this is that, for example, a "checkerboard pattern" of white and black pixels does not look the same as an area of half-gray pixels in brightness. This is due to the difference between luminous and radiant flux.) What's worse, reducing color images to an image with less colors while preserving perceived brightness of the colors is a lot more complicated.

But in computing, this is only half of the issue. The other half is the display device. You see, display devices don't emit light in a linear manner either. And to complicate things, different displays may have different emission curves. This means that without any kind of correction the exact same image may look noticeably different with different displays.

For the casual user this seldom makes a significant difference. However, for professional graphics artists, publishers and so on it can make a huge difference. If you, for example, design a beautiful image for the cover of a magazine in your computer, and then when it's printed you find out that the white balance and color balance are completely off in the printed version, you won't be very happy. And this is just one example of many.

Gamma correction is an attempt to fix this issue. Its intent is that if an image file has gamma correction data in it, the image will always look (nearly) identical in all (properly-configured) systems regardless of the differences in the physical properties of their hardware.

(The most common gamma for modern displays is 2.2. Quite curiously this corresponds very roughly to the perceived brightness of the human eye as well. This means that a pixel with relative RGB values of (0.5, 0.5, 0.5) will look approximately half as bright as a pixel of (1.0, 1.0, 1.0). In other words, the relationship between physical pixel values and perceived brightness is almost linear. This is quite convenient.)

The problem is that gamma handling has never been universally standardized, and it has become a complete and utter mess. There isn't even a universal agreement on which part of the entire system should be handling the gamma correction. Should it be the image file itself? Should it be the image viewer program? The operating system? The display driver? The graphics card? The display itself? Obviously if two of these (or anything in-between) ends up doing gamma correction, you will end up with over-correction, and the image will look like crap. (The difference between gammas 1.0, ie. no correction, and 2.2 is extremely visible. It's not like it's something subtle that only a trained eye can see.)

The PNG image file format is infamous for messing up gamma correction really badly. It almost ended up destroying the popularity of the file format.

By far the most common use for PNG images is in web design. Usually web pages do not care about gamma correction of its images, and instead aim for a consistent visual design.

What was one of the major problems related to this? Well, imagine that you make a web page that has a background color of (128, 128, 128), and you have a PNG image with some pixels having the color (128, 128, 128). Obviously you would expect the two colors to look identical, and would often rely on this when designing a web page. Often (especially when PNG was still new) you would be wrong, and ended up with the PNG's half-gray looking completely different from your web page's half-gray background. Why?

Because the creators of the PNG format wanted to support gamma correction, did it poorly, and the whole thing got extremely messy.

Some web browsers supported the gamma info in PNG files, while others didn't. This meant that if the PNG had gamma info in it, it would look different in different browsers.

Fine, just leave the gamma info out of the PNG completely. The file format supports that. But no, and here comes the screwup. You see, the PNG standardization committee stipulated that if a PNG file has no gamma information, the software displaying the image should nevertheless use an assumed gamma value.

Of course some browsers implemented this standard, while others didn't. So even if you left the gamma info completely out of the PNG file, it would still look different in different browsers. (And, what's worse, the half-gray in the PNG would look different than the half-gray page background color in the standard-conforming browsers. And if you tried to fix that with the PNG file, it would look different in the non-standard-conforming browsers.)

Needless to say, none of this was a problem with either GIF or JPEG, neither of which had any gamma info messing things up to begin with.