interpolation/filtering graph software toys

[Katie Boundary]

Wikipedia articles on interpolation and filtering sometimes have pretty graphs to help people understand just what the hell they're talking about. Here are some examples relating to linear, cubic, and Lanczos interpolation, respectively:

https://scontent-ord1-1.xx.fbcdn.net/v/t1.0-9/13442159_1702009600063495_6076545671406639562_n.jpg?oh=7446e1a9ce81474e4f214599b130cbfd&oe=57C96EA0

https://scontent-ord1-1.xx.fbcdn.net/v/t1.0-9/13413112_1702009606730161_4575129552020894739_n.jpg?oh=3ec3df4b3f8e906f0a40a2f1f44c6490&oe=57CC0E4E

https://scontent-ord1-1.xx.fbcdn.net/v/t1.0-9/13178660_1685820068349115_8144483403571673480_n.jpg?oh=7969d976c6571cb0e3891db72d727e17&oe=57E7411E

Unfortunately, I can't find anywhere near enough pics to determine the answers to certain questions too numerous and specific to bother you all with individually. I was therefore wondering if there were any online software toys that would, if given a bunch of sample values and an interpolation or filtering method, show what the reconstructed waveform looks like.

Also... the Lanczos curves with odd numbers of taps look "droopy", and Lanczos-2 looks the opposite (kind of balloony). Does this mean that the former will artificially darken an image, and Lanczos filters with an even number of taps will artificially lighten it?

[colours]

Could you maybe not reupload images from Wikimedia's servers to Facebook?

If you want to look at how certain inputs are interpolated, you can already do that with any semi-decent graphing program. Just feed all the formulae to the graphing program and let it do all the work for you.

Explicit normalisation of the interpolation coefficients is usually done in resizers to avoid that very problem of inconsistent brightening/darkening. (Cf. point 5 in "How to make a resampler that doesn't suck" (http://www.virtualdub.org/blog/pivot/entry.php?id=86).)

ResampleHQ's documentation (http://svn.int64.org/viewvc/int64/resamplehq/doc/kernels.html) has graphs of all of the impulse responses of AviSynth's built-in resizers. Note that while the graphs are accurate, the descriptions of "blurring", "sharpness" and "ringing" are completely nonsensical and you should ignore those.

[filler56789]

Could you maybe not reupload images from Wikimedia's servers to Facebook?

Evidently, Katie just ignores the fact that Facebook shamelessly ruins every image file that the users upload to the Akamai servers... The JPEG quantization matrices which Facebook uses for recompressing are simply *intolerable*.

[Katie Boundary]

So last night, about half an hour after logging off, I realized that 1-tap windowed sinc filters are actually just approximations of Hermite (kind of like how 2-tap windowed sinc and Lagrange order 3 are both approximations of Catrom). It blew my primitive dinosaur mind.

That's not really more than tangentially related to anything being discussed here but I felt like sharing. Also, I didn't sleep last night and probably shouldn't be posting right now.

you can already do that with any semi-decent graphing program

Oh no, that absolutely won't suffice. I need the name of a crappy graphing program.

</sarcasm>

Explicit normalisation of the interpolation coefficients

I dunno what that means lol.

ResampleHQ's documentation (http://svn.int64.org/viewvc/int64/resamplehq/doc/kernels.html) has graphs of all of the impulse responses of AviSynth's built-in resizers.

I don't really know what an impulse response is, either... I do see a lot of filter shapes, though! :)

Evidently, Katie just ignores the fact that Facebook shamelessly ruins every image file that the users upload to the Akamai servers...

Yes, I do. Can we get back on topic, please?

[Groucho2004]

</sarcasm>
I see you finally set the sarcasm closing tag. Where is the opening tag? In one of your first posts on this forum? That would explain a lot. :D

[Katie Boundary]

I see you finally set the sarcasm closing tag. Where is the opening tag? In one of your first posts on this forum? That would explain a lot. :D

Never change, Groucho :)

[colours]

Oh no, that absolutely won't suffice. I need the name of a crappy graphing program.

I was going to suggest use Google, you idiot, until I actually searched for "graphing program" myself and none of the results on the front page even allow defining custom functions. What the hell, Google.

You can rig FooPlot for this purpose, but since you don't know JavaScript this is probably out of the question. I sometimes use KmPlot, but I doubt that's an option for you too.

I dunno what that means lol.

There is a link after that sentence you quoted. Scroll to section 5 and read the second paragraph.

Actually, no, just read the whole thing. It's barely two pages long.

Yes, I do. Can we get back on topic, please?

No, because the JPEG compression (the chroma subsampling, to be more precise) looks absolutely terrible and posting such images should be a bannable offence.

[Groucho2004]

I need the name of a crappy graphing program.
Whenever I have to create a graph from some data I use either Excel or LibreOffice Calc. Comes with some templates and is easy to use.