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• The perfect crossfade

  - by epologee

  I find it hard to describe this problem in words, which is why I made a video (45 seconds) to illustrate it. Here's a preview of the questions, please have a look at it on Vimeo: http://vimeo.com/epologee/perfect-crossfade The issue of creating a flawless crossfade or dissolve of two images or shapes has been recurring to me in a number of fields over the last decade. First in video editing, then in Flash animation and now in iOS programming. When you start googling it, there are many workarounds to be found, but I really want to solve this without a hack this time. The summary: What is the name of the technique or curve to apply in crossfading two semi-transparent, same-colored bitmaps, if you want the resulting transparency to match the original of either one? Is there a (mathematical) function to calculate the neccessary partial transparency/alpha values during the fade? Are there programming languages that have these functions as a preset, similar to the ease in, ease out or ease in out functions found in ActionScript or Cocoa?

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• Draw images with warped triangles on a web server [migrated]

  - by epologee

  The scenario The Flash front end of my current project produces images that a web server needs to combine into a video. Both frame-rate and frame-resolution are sizeable enough that sending an image sequence to the back end is not feasible (in both time and client bandwidth). Instead, we're trying to recreate the image drawing on the back end as well. Correct and slow, or incorrect and fast The problem is that this involves quite a bit of drawing textured triangles, and two solutions we found in Python (here and there) are so inefficient, that the drawing takes about 60 seconds per frame, resulting in a whopping 7,5 hours of processing time for a 30 second clip. Unacceptable. When using a PHP-module to send commands to ImageMagick for image manipulation, the whole process is super fast (tenths of a second per frame), but ImageMagick seems to be unable to draw triangles the way we do it in the front end, so the final results do not match. Unacceptable. What I'm asking here, is if there's someone who would know a way to solve this issue, by any means necessary that would run on a web server. Warping an image Let me explain the process of the front end: Perform a Delaunay calculation on points in an image to get an evenly distributed mesh of triangles. Offset the points/vertices in the mesh, distorting or warping the image. Draw the warped triangles on a new bitmap. We can send the results (coordinates) of steps 1 and 2 to the back end, to then draw the warped triangles and save it to an image on disk (or append as a frame to the video). But that last step is what I need help with. The Question Is there an alternative to ImageMagick that can draw triangles in a bitmap? Is there some other library, like a C library, that would allow us to do this? Or could we achieve this effect more easily by switching back end technologies, like Ruby? (.Net and Java are, unfortunately, not really options right now) Many thanks. EP. P.S. I'd appreciate re-tagging efforts, I don't quite know what labels to put on this question. Thanks!

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