Wolfram Mathematica - 2012-02-11 (page 2 of 2)

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5:25 PM

Someone on MathGroup told me he saw some links to this site in some posts, but didn't bother as he though it was just StackOverflow. The current state of the StackOverflow mathematica tag doesn't give a very positive picture.

Perhaps we should put this new site into our signatures now

@Szabolcs done!

user image

nice round numbers

Why do people think this is not broad? At least, the title is. Given that he narrowed down the question to changing the colours of an image, only acl's answer answers it... editing the title will invalidate the others

5:41 PM

The original question was "Question: Is it possible to process image data in Mathematica on a pixel to pixel basis. If yes, then where are the examples to learn more on the subject?"

I don't see how (say) ImageEffect really answers that. So it's not really a question of him changing the question after the fact.

actually I think his real question was "how do I get a list of the image data in some easily manipulated form", the answer to which is ImageData

I too believe that's the question he wanted to ask... your point about his rephrasing not necessarily being the cause is also taken

@yoda If my vote weren't binding I'd have voted to close myself...

ah, the moderator's eternal dilemma :)

Now I'm not saying Brett's answer or Mr.Wiz's are unhelpful — they certainly do highlight parts of mathematica's capabilities/link to resources. but I feel that it's the question that led to those and such questions are not what we should be gunning for.

"it's the question that led to those and such questions are not what we should be gunning for." - Precisely. Good answers do not make a good question.

(actually the guys at MO had a better phrasing, which escapes me now...)

well, we can either a) fix the question or b) close and delete it

(a) is tricky, as it will invalidate some of the answers there

so, (b)?

5:55 PM

Well, who's up for a heroic edit?

JM can delete it once it's closed, can he not?

Should it be deleted as well? Why not just close it?

what purpose does closing serve now?

(it's a real question I am asking!)

@acl I'm not too fond of deleting, since I like yours and Brett's answers... but if the lot of you think it's a broken window, then alright...

@JM Well, someone would have to put in quite a bit of effort to reword it so it's not too broad while simultaneously not invalidating two rather different answers

6:00 PM

@acl Closing just prevents new answers from being added. Which I think is warranted here...

OK, I see. Well, whatever the rest of you decide.

@JM And closing it sends a signal about the question itself.

good, so we close it then?

If two more people can serve as jurors for that question, I'll be a willing executioner.

I've just voted to close

6:04 PM

2

Q: How can I extract the data from an image and process it pixel by pixel?

For example, to change the color of each pixel to the mean color of the three channels, I tried i = ExampleData[{"TestImage", "Lena"}]; Mean[i] but it just remains unevaluated: How can I read the colors of an image into a list or matrix and change the color codes and save it back to an image?

image-processing

I voted to close as "not a real question" (I don't see it as inviting debate, for instance, so "not constructive" didn't seem to fit)

THWACK!

hm

so, RM edited it just as it was being closed

ha

You guys can vote to reopen if you wish, y'know... ;)

Speaking of Lenna... I only recently found out that I actually have a copy of *that* magazine where she showed up. Collector's item!

@JM Apparently that was the best-selling playboy issue ever

6:12 PM

How can I input ↦ on a mac (other than using character viewer)?

I kind of miss the Alt+keycombo for unicode characters on windows and linux

@yoda in Mathematica?

Perhaps I just don't know what the equivalent is on a mac

@JM no, just on a mac (text editor)

@yoda hm doesn't seem to be a shortcut for that

I'm sleepy, and I'm done writing my latest blog entry, so: see you guys later, and be nice! ;)

@acl Yeah, I figured... it's not just that one in particular, but any unicode. Sometimes, it's nice to use arrows and stuff instead of resorting to -->...

6:22 PM

@yoda If you set the keyboard source to Unicode Hex Input in Settings > Language&Text > Input sources you can enter unicode characters with Alt+<hex code>

perfect! Was just fiddling around in that section

@yoda My answer was aimed at the "Background: I just saw a program that converts images to cartoons." portion of the "question". But it was incredibly vague.

@yoda You can set a keyboard shortcut to rotate between different input sources if you have more than one

Time to go get lunch and then run errands..

@Heike Seems necessary... I also use the regular option-char shortcuts sometimes

@BrettChampion Yeah, I figured... Again, not blaming you or the answer (which indeed was useful), but just trying to understand and get a consensus as to what we expect of questions

6:28 PM

I don't think I'll ever reach 10000 on Stackoverflow. It seems that whenever I answer a question there it gets migrated here.

@Heike :)

I was content with my pace on SO, until yoda sped past me, then you did so also ... :P

@Heike look at it this way... you'll earn rep faster here... people who vote there can vote again here

@rcollyer i was lazy until you made it a contest out of thin air!

@yoda I was trying to bypass you on the list. Then, well, you told Chewy to punch it.

ruuuuuurrrgh

@yoda True, but now that I have access to mod tools here I was hoping I would get there on SO eventually.

6:36 PM

@Heike you'll lose all hope in humanity. you do not want to see what lies in SO's dungeon

@rcollyer Who's Chewy?

@Heike I've given up trying for them on SO. I hope to get them soon here, and keep them.

@yoda I already lost hope at the supermarket today.

user image

Chewbacca, also known as Chewie, is a fictional character in the Star Wars franchise, portrayed by Peter Mayhew. In the series' narrative chronology, he appears in Episode III: Revenge of the Sith, Episode IV: A New Hope, Episode V: The Empire Strikes Back and Episode VI: Return of the Jedi. He guest starred on the season 3 finale on Star Wars: The Clone Wars. Creation Chewbacca's creation as a "gentle, hairy, non-English-speaking co-pilot" was inspired by George Lucas seeing his own dog sitting up on the passenger seat of Lucas' car. The dog, named Indiana, also inspired the name of t...

6:37 PM

see... this is why you lost on SO.

I know him, I thought he was a user on SO

@Heike entirely possible.

@Heike just share a link to "How can I find waldo" on reddit again... those folks there have a short memory

of course, looking up Chewbacca, I found this

Chewbacca defense

The Chewbacca defense is a legal strategy used in episode 27 of South Park, "Chef Aid", which premiered on October 7, 1998, as the fourteenth episode of the second season. The aim of the argument is deliberately to confuse the jury by making use of the fallacy known as ignoratio elenchi, or a red herring. The concept satirised attorney Johnnie Cochran's closing argument defending O. J. Simpson in his murder trial. The Associated Press noted the satire as an example of Cochran's position in popular culture. The concept has become a minor Internet phenomenon, used frequently as a runn...

see you later

adios

6:40 PM

@yoda rather not. I still feel rather embarrassed over that whole waldo thing.

lol

don't be. It was a good answer to the question... we can't control what goes viral and what doesn't. If we weighted answers truly by worth, WReach should already be at 2k instead of just some 150 above me

@yoda I still don't understand the dynamic of upvoting

@JM I didn't know it was possible to extend RandomReal / RandomInteger !

@Heike It's mostly user dependent, but can be narrowed down to a few classes — some people upvote stuff that they can understand. If you didn't have step by step images, someone who didn't understand image processing/mathematica would've have been able to follow. This is also the reason why short and quick answers for simple questions get lots of upvotes... people can grok the answer in one pass in under 2 seconds, and so can click the button right away.

Sometimes I don't upvote because I don't have the time to go through the answer and understand it

6:49 PM

Write a detailed, in depth answer like Leonid's, and it flies past a lot of users. Some are dedicated and save the page and come back later... that's why you see his answers gain upvotes slowly, but surely, whereas the quick and dirty ones won't gain upvotes after the hype has died down. Others mean to come back to understand, but either don't have the time or forget

@yoda I often upvote answers I would have given had I not been beaten to it.

Some upvote only if it is something they didn't know or "worthy" of an upvote for various definitions of worthy. Some use it as a means to balance the upvotes on the answers (i.e., answer A already has a lot of upvotes and does not "deserve" more). I personally find this behaviour extremely annoying and think it's unhealthy... yet, they too have a place in the ecosystem

Others upvote if it's correct and mostly for effort or answering the question, regardless of "difficulty level". I tend to do this. For very complicated answers, I try to follow the logic and if I can reach half way or understand the gist of it, I upvote.

People attach various meanings to upvotes on questions and answers... but if you actually hover on the tooltip, it says "this answer was helpful" and "this question shows effort" or something like that...

With me it's a mix of all the above I guess.

It's just that it can be a bit frustrating to put a lot of effort in an answer and only get half the number of upvotes that some of the 10-second answers get.

3

True, that hurts. Unfortunately, there's no solution for that :(

It has been discussed often as to how to deal with these issues (e.g., weighting votes from high rep users or users of the tag more heavily than the others, etc.), but they've all been declined

7:06 PM

@yoda I guess you already need a certain amount of rep to be able to up or down vote in the first place

@Heike up is ridiculously low... 15 rep is all you need.

@Heike Do you remember my question in the morning about why graphics are slow to show? The bottleneck is ToBoxes , and Compress adds a little to that (large graphics are sent to the front end compressed)

ToBoxes might take much longer than the rendering itself

Let me make another Koch curve experiment (that was the first instance I complained that Mathematica 6 is so much slower to show graphics than version 5)

at least, the waldo question netted me a silver "pundit" badge =)

meh, Chrome and Time Machine aren't playing nicely together it seems

@yoda That limit is pretty useless. Confirming your email address gets you 50 points already if I remember correctly

@Heike no, that's only for Area51

the other sites don't require you to confirm your email

7:21 PM

@yoda Oh, ok

I did get 100 bonus rep for having enough rep on SO.

It seems I can optimize conversion to boxes for simple cases:

Right, that's to help you avoid initial inconveniences like not being able to comment/upvote because you've already proven "useful" elsewhere

This is the Koch curve code:

rotate90[{x_, y_}] := {-y, x}

koch[p1_, p2_, n_] := {koch[p1, p1 + (p2 - p1)/3, n - 1],
  koch[p1 + (p2 - p1)/3, (p1 + p2)/2 + Sqrt[3]/6 rotate90[p2 - p1],
   n - 1], koch[(p1 + p2)/2 + Sqrt[3]/6 rotate90[p2 - p1],
   p2 - (p2 - p1)/3, n - 1], koch[p2 - (p2 - p1)/3, p2, n - 1]}

koch[p1_, p2_, 0] := Line[{p1, p2}]

g = Graphics[koch[{0., 0.}, {1., 0.}, 8]]; // Timing
AbsoluteTiming[ToBoxes[g];]
NotebookWrite[EvaluationNotebook[],
   Cell@BoxData[
     g /. Dispatch[{Line -> LineBox,
        Graphics -> GraphicsBox}]]]; // AbsoluteTiming

@Heike Please see above

@Szabolcs Strange that ToBoxes is so slow. I thought that Graphics3D and Graphics3DBox are pretty similar.

That NotebookWrite shows the graphics much more quickly on my machine than just evaluating g

7:27 PM

I get timings of 10.2 vs 2.6 seconds

Of course I am only replacing the Line and Graphcis symbols, nothing else

Does anyone know how to force rendering to happen on the GPU without explicitly including a graphics element that requires it (such as a Polygon with VertexColors)?

For this Koch curve rendering on the graphics card is not significantly faster than rendering on the CPU, but looks much worse

8:06 PM

The title of this page says "SQLExecute - Wolfram Mathematica 9 Documentation"

Do you see this too? Is it an oversight?

The documentation of other SQL functions also has Mathematica 9 in their title

I just bought a license so I hope they wait a bit with bringing out version 9

@Heike in my experience with buying stuff, this guarantees v9 is around the corner

but in a superficial comparison I do not see any difference between that documentation and the one in my version of mma. which doesn't mean much (maybe DatabaseLink hasn't changed, maybe I missed the changes, etc)

@acl Versions 7 and 8 were published in November 2008 and November 2010 respectively, so I was gambling on a release date in November 2012 for version 9

On the other hand, if they bring it out within the next 2 weeks, I could return this license under the 30 day money back guarantee.

8:25 PM

@Heike is this a home license? I think they have some upgrade pricing which is not unreasonable (although I suppose if it's been a month since you bought it you may still not be happy about it)

@acl yes it is.

Maybe the version number is automatically included and someone ran the documentation generator in a development version by accident

9:03 PM

Hmmm, a new badge is available.

9:17 PM

This documentation issue also happened several weeks before M8 launch, and so we can be close to the launch of M9. I was also thinking that we would have M9 by the end of the year, but last week I also saw this M9 pages (seeing no difference on the actual content as happened before M8 launch)...

too bad there aren't any WRI employees around who would be able to tell us more ...

Hmmm. Interesting.

That would be good news for me, as I will have to buy a license this summer.

9:33 PM

I think all of them have to sign an NDA so they wouldn't be able to give any info anyway

@Szabolcs I'm pretty sure of that.

I'm buying a license next week! But, correct me if I'm wrong, when we have premier service we have all updates; correct?

Don't know.

I'm glad to still be in school. Costs me a lot less than some other licenses.

@PFonseca According to this you get free upgrades, but I guess you could always call customer service to be sure.

@CHM don't forget to have an active student license before you get out of school. If you have, you will most likely be able to negotiate an upgrade to the professional thing, by just signing to the premier service...

@Heike will definitely call them

9:50 PM

@PFonseca I will see what I can do. I still have at least 2 years left, so it shouldn't be a problem.

1 hour later…

10:56 PM

@CHM please let me know what the error in my answer is. I am on an iPad right now and cou,d not check

@Verbeia a closing bracket is missing

@Both that's not the problem.

Well, it is. But it doesn't work, even after adding the bracket.

as I don't know each function you used, I'm looking up in the knowledge base to spot the error.

@Verbeia what does Flatten[expr, {0}] do?

Error is "Flatten::flpi: Levels to be flattened together in {{0}} should be lists of positive integers. >>

Join::heads: Heads Flatten and List at positions 1 and 2 are expected to be the same. >>

Join::heads: Heads Flatten and List at positions 1 and 2 are expected to be the same. >>"

@Verbeia Do you mind if I edit your post?

@acl A bracket is missing, you must close the Flatten before the {0}

11:04 PM

@Szabolcs oh right

Please do, I have lots of trouble getting the syntax right when I am typing from memory on the iPad. But I knew Outer was a good solution to the question because of the relationship between a and b.

closed it at the wrong place and got stuck in a local minimum and kept trying to figure that out

@Verbeia I made an edit and replaced the Table/Flatten with a Partition

this way there are no restrictions on the list length's evenness or oddness

does my English sound odd? :-)

That's how I would say it too. Cue joke about whether australians really speak English. :-)

Thanks!

@Szabolcs I would have used parity.

11:10 PM

@Heike Thanks!

Bedtime for me, bye all! Must be up early tomorrow.

good night

is using # and @ in an expression considered pattern-matching?

as in Mr. Wizard's answer: PadRight[#, Length@#[[1]], #] & @ {a, b}

11:30 PM

@CHM No. The operator @ is used for writing function calls in prefix notation. f@x is actually the same as f[x]. The expression PadRight[#, Length@#[[1]], #] & is a pure function where # is its first argument. This expression could also have been written as Function[{x}, PadRight[x, Length[x[[1]]], x].

@Heike Oh. I see

It's a lot more elegant to use @ and #, or so it looks.

@Szabolcs Tsk, I knew I forgot to include something in the blog entry... see here for the method plug-in framework for Random[] functions.

Off to play hockey.

@CHM I can be, but it can obfuscate things as well.

-22 outside, it's gonna hurt.

Bye.

11:39 PM

Hmm, I don't understand how Wizard's answer is different from the second part of Heike's answer...

Celsius I hope

@JM It isn't. Given his comment I think he missed my second answer

I left a comment...

I just noticed.

11:56 PM

@Heike Sometimes it seems that making an answer complete actually makes it less likely to be upvoted... yech.

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