Archiv des Autors: christian

Most Popular Posts and Tags

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I have added a per­ma­nent page with a sum­ma­ry of the most pop­u­lar posts on this blog. I also tried to add mean­ing­ful tags to all posts. Here are the most impor­tant tags:

Content type tags

  • down­load — a down­load is avail­able is this post
  • gem — a code snip­pet or oth­er copy-paste thing is available
  • math — posts that are heavy on math formulae

Topic tags

So, where are the stars?

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In my pre­vi­ous rant about dynam­ic expo­sure in Elite Dan­ger­ous (which hon­est­ly applies to any oth­er space game made to date), I made a rough cal­cu­la­tion to pre­dict the bright­ness of stars as they should real­is­ti­cal­ly appear in pho­tos tak­en in out­er space. My pre­dic­tion was, that,

  • for an illu­mi­na­tion of sim­i­lar strength to that on earth,
  • if the sun­lit parts are prop­er­ly exposed,
  • and with an angu­lar res­o­lu­tion of about 2 arc min­utes per pixel,

then the pix­el-val­ue of a promi­nent star should be in the order of 1 to 3 (out of 255, in 8‑bit sRGB encod­ing). Since then I was curi­ous to find some real world val­i­da­tion for that fact, and it seems I have now found it.

ISS_and_Endeavour_EV+0

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\usepackage{cmbright}

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The ‘mod­ern’ look­ing sans-serif font I use recent­ly in \text{\LaTeX} equa­tions on this blog is called ‘Com­put­er Mod­ern Bright’, and actu­al­ly is not so mod­ern at all: Designed by Wal­ter Schmidt in 1996, it is still to date the only free sans-serif font avail­able for \text{\LaTeX} with full math sup­port. Type‑1 ver­sions of this font are avail­able in the cm-super pack­age, but I did­n’t need to install any­thing, because appar­ent­ly, the Quick­La­TeX Word­Press plu­g­in has them already. The only thing to do was adding just one line to the preamble:

\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{cmbright}   % computer modern bright

I also turned on the SVG images fea­ture that was added with ver­sion 3.8 of Quick­La­tex, so the equa­tions are no longer pixel­lat­ed on reti­na dis­plays or when zoom­ing in! Neat, huh?

Elite Dangerous: Impressions of Deep Space Rendering

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I am a backer of the upcom­ing Elite Dan­ger­ous game and have par­tic­i­pat­ed in their pre­mi­um beta pro­gramme from the begin­ning, pos­i­tive­ly enjoy­ing what was there at the ear­ly time. ‘Pre­mi­um beta’ sounds like an oxy­moron, pay­ing a pre­mi­um for an unfin­ished game, but it is noth­ing more than pur­chas­ing the same backer sta­tus as that from the Kick­starter cam­paign.

I came into con­tact with the orig­i­nal Elite dur­ing christ­mas in 1985. Com­pared with the progress I made back then in just two days, my recent per­for­mance in ED is lousy; I think my com­bat rat­ing now would be ‘com­pe­tent’.

But this will not be a game­play review, instead I’m going to share thoughts that were inspired while play­ing ED, most­ly about graph­ics and shad­ing, things like dynam­ic range, sur­face mate­ri­als, phase curves, ‘real’ pho­tom­e­try, and so on; so … after I loaded the game and jumped through hyper­space for the first time (actu­al­ly the sec­ond time), I was greet­ed by this screen fill­ing disk of hot plasma:

ED001

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X‑Plane announces Physically Based Rendering

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I always won­dered when X‑Plane would jump on the PBR band­wag­on. I like X‑Plane, I think its the best active­ly-devel­oped* flight sim­u­la­tor out there, but I always felt that shad­ing could be bet­ter. For instance, there is this unre­al­is­tic ‘Lam­bert-shad­ed’ world ter­rain tex­ture, which becomes too dark at sun­set; anoth­er is the dread­ed ‘con­stant ambi­ent col­or’ that plagues the shad­ing of objects.

Now in this post on the X‑Plane devel­op­er blog, Ben announces that Phys­i­cal­ly Based Ren­der­ing is a future devel­op­ment goal, yay! Then he goes on to say that, while sur­face shad­ing will be a solved prob­lem™ because of PBR, oth­ers like par­tic­i­pat­ing media (clouds, atmos­phere) would still need mag­ic tricks for the fore­see­able future. Weit­er­lesen →

Journey into the Zone (Plates)

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I have exper­i­ment­ed recent­ly with zone plates, which are the 2‑D equiv­a­lent of a chirp. Zone plates make for excel­lent test images to detect defi­cien­cies in image pro­cess­ing algo­rithms or dis­play and cam­era cal­i­bra­tion. They have inter­est­ing prop­er­ties: Each point on a zone plate cor­re­sponds to a unique instan­ta­neous wave vec­tor, and also like a gauss­ian a zone plate is its own Fouri­er trans­form. A quick image search (google, bing) turns up many results, but I found all of them more or less unus­able, so I made my own.

Zone Plates Done Right

I made the fol­low­ing two 256×256 zone plates, which I am releas­ing into the pub­lic so they can be used by any­one freely.

Cosine zone plate with constrast weighting

Cosine zone plateCC0

Zone plates with contrast weighting

Sine zone plateCC0

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Ego mecum conjungi …

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… Twit­ter!

Twitter_logo_blue

So out of a whim I just embar­rassed myself and tried to write in (prob­a­bly wrong) latin that I joined twit­ter. You can fol­low me under: @aries_code.

If you won­der how this came about, this was my train of thought:

  • Twit­ter has some­thing to do with birds
  • Birds have fan­cy latin species names
  • The species name for Spar­row is Spass­er domesticus
  • This does­n’t sound too fancy …
  • How do you say ‘I joined twit­ter’ in latin anyway?

But then I dis­cov­ered that I am onto some­thing: Accord­ing to one argu­ment, the brand name of Twit­ter should have been ‘Titi­a­tio’, had it exist­ed in antiq­ui­ty. And accord­ing to anoth­er argu­ment, latin should be an ide­al twit­ter lan­guage, because it is both short and expressive.

But I digress. If you are into com­put­er graph­ics, then you know of Johann Hein­rich Lam­bert, the eponym of our beloved Lam­bert­ian ref­electance law. The book where he estab­lished this law, Pho­tome­tria, is writ­ten entire­ly in latin—now this is hardcore!

So, now you know what to do if you want to stand out in your next SIGGRAPH paper …

Yes, sRGB is like µ‑law encoding

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I vague­ly remem­ber some­one mak­ing a com­ment in a dis­cus­sion about sRGB, that ran along the lines of

So then, is sRGB like µ‑law encoding?

This com­ment was not about the col­or space itself but about the spe­cif­ic pix­el for­mats nowa­days brand­ed as ’sRGB’. In this case, the answer should be yes. And while the tech­ni­cal details are not exact­ly the same, that anal­o­gy with the µ‑law very much nails it.

When you think of sRGB pix­el for­mats as noth­ing but a spe­cial encod­ing, it becomes clear that using such a for­mat does not make you auto­mat­i­cal­ly “very picky of col­or repro­duc­tion”. This assump­tion was used by hard­ware ven­dors to ratio­nal­ize the deci­sion to lim­it the sup­port of sRGB pix­el for­mats to 8‑bit pre­ci­sion, because peo­ple “would nev­er want” to have sRGB sup­port for any­thing less. Not true!Screen Shot 2014-03-06 at 19.02.54I’m going to make a case for this lat­er. But first things first.

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