Blog, Photos, Videos and Other | Giovanni Di Grezia - VFX Artist

Filter Contents

All

Blog

DSLR

Instagram

Bloody Day

On October 28, 2014 in Blog, Detailed Portfolio

The main target of the project is the creation of a cg helmet (with references to a real one) to put on the head of a driver. For the shot i used a Nikon D3200 with a 18-55 lens. Yes, rolling shutter. I placed some white circular trackers on the background due to the film grain. The sensor isn't too much good and it has made necessary the use of trackers. I have encountered some problems, all explained in the next section, about the camera tracking (due to low parallax shift of static points), cars and other objects on markers (rotoscoping needed), problematic tracker removal on the wall(because of visibility of some markers through a car windows) and the presence of some red markers and a spring around the neck(removed with clone). I have also committed some errors during the shot, i brought with me a checkerboard to estimate the focal length but i forgotten to make a photo and so i had to resolve the camera 2 times, I also placed some little red markers on the close wall but they were too little and untraceable after a first review, these errors have made the entire resolution a bit tricky but i hope you like the final result

Full video at 60 fps

21mbit video at 59,94 fps – h264 – 1280 x 720 Progressive

Loading the player ...

Adopted Workflow

Placing of Markers (smaller closer and larger on the distant wall) – FAILED ON CLOSE WALL
Placing of Markers on the hood (Driver’s head)
Retention of the distance of a pair of background trackers and hood trackers for a correct scene scale
Testing of a possibile shots and choice of a fixed focal length
Different shots at 59fps, hd to reduce the rolling shutter on the sensor (less lines to scan)
Some 360 photos for HDR reconstruction, needed for a correct illumination and the reflex on the helmet
Some 360 photos for the Helmet reconstruction.
Removal of Rolling Shutter, Camera Tracking and estimation of the focal length (MISSING CHECKERBOARD REFERENCE)
Again, from the source, Removal of Lens distortion calculated from the previous step, Rolling Shutter, Camera Tracking, Object Solving, Scene scale and export
Removal of Distorsion on the helmet shots. Camera tracking, export
Modeling of the Helmet, creation of multiple uvs ids, texturing, painting
Scene HDR creation and tone mapping.
Integration of the helmet in the scene, animation, lighting and rendering (material passes, ambient occlusion, object mattes,motion blur vectors)
Compositing, trackers removal and general fixes.
Color grading.

Bloody Day - Making of and Passes

Problems and fixes

Red markers and the spring around the neck

Trackers through car windows

HDR References

Object Reconstruction References

Head Reconstruction

Camera Tracking References

DSC_0035

DSC_0036

DSC_0037

DSC_0038

DSC_0039

DSC_0040

DSC_0041

DSC_0042

DSC_0045

DSC_0046

DSC_0047

DSC_0048

DSC_0049

DSC_0050

DSC_0051

DSC_0052

DSC_0054

Backstage

DSC_0043

DSC_0053

DSC_7643

DSC_7644

DSC_7645

DSC_7647

DSC_7649

DSC_7651

DSC_7653

DSC_7655

DSC_7658

DSC_7661

DSC_7664

DSC_7665

DSC_7667

DSC_7670

DSC_7672

Splines

On October 28, 2014 in Blog, Compositing

Maniglie e tangenti

Le spline sono linee digitali create dai differenti software di computer grafica. Matematicamente le spline vengono generate grazie ad equazioni vincolate da punti chiamati control points o control vertex. Questi punti determinano l’andamento della curva. Le spline sono usate in molti ambiti, dal semplice fotoritocco per nascondere parti di immagini fino al complesso rotoscoping per i film.

Per ogni punto della spline abbiamo una maniglia, handle, che ci permettere di modificare l’andamento della curva passante per il punto scelto. Queste maniglie sono tangenti alla curva e la lunghezza ne determina la pressione sulla curva. Una maniglia si definisce morbida se entrambi i segmenti della tangente (a sinistra e a destra del punto) fanno parte della stessa linea. L’allungamento dei segmenti ne comporta una variazione nella pressione sulla curva aumentando o diminuendo la curvatura della spline in prossimità del punto.

Curvatura

Le maniglie possono venir spezzate in due segmenti aventi in comune solo un punto della curva. La maniglia definita broken romperà quindi l’assetto di curvatura della spline regalando un comportamento asimmetrico e una maggiore flessibilità per l’utente.

La curvatura della spline può essere linear, bicubic, etc. Un curvatura lineare fa si che le linee che congiungono due control point siano segmenti. Bicubic invece ne assicura una maggiore interpolazione prendendo più punti in considerazione.

Ogni punto può essere animato singolarmente in ogni frame ma in generale conviene valutare il sorgente prima di spostare punti a caso. Se stiamo tracciando il contorno di una immagine che varierà prospetticamente di poco nel video, ci converrà operare sulla traslazione, rotazione e scala dell’intera curva anziché operare sui singoli cv.

Il workflow è infatti quello di agire sulle componenti matriciali di tutta la curva per poi migliorare ogni singolo cv in un secondo momento, ereditando le trasformazioni dell’oggetto. Più difficile a dire che a fare ma è importante capire che analizzare un footage è di estrema importanza. Buttarsi su un rotoscoping di 1000 frame muovendo ogni singolo cv può essere dispendioso in termini di tempo e insoddisfacente in tempi di qualità; i cv potrebbero vibrare e muoversi indipendentemente dalle forme dell’oggetto rendendo la maschera imprecisa e fastidiosa da vedere.

Shutter Angle, Shutter Speed and Motion Blur

On September 13, 2014 in Blog, Compositing, VFX

These words are stricly connected. You can’t have Motion Blur with fast Shutter Speed and the Shutter Speed is another name of the Shutter Angle. There are some rules you shouldn’t break. You don’t have to shoot with a ( 1/shutter speed ) less than frame rate. In some cameras, shutter is real and for other ones is virtual. A dslr has a mirror for a single image (shutter). For videos the shutter is digital. How convert shutter speed in shutter angle? The key is the frame rate.
Shutter Angle / 360 = Frame rate * Shutter Speed.
This is the formula. So for example : If i shoot at 1/125 sec at 59.94 fps, i have a shutter angle of 172 degrees. Equivalent to 69 degrees if shooted at 24 fps. In some cg softwares you have to put the length of the shutter, usually this is the Frame rate * Shutter Speed. Most of them consider this value calculated from a fixed frame rate of 24 fps. So when you try to insert the value (Frame rate * Shutter Speed), you should calculate the formula using 24 insted of your shooted frame rate.
On the example above, the value ( 59.94 * (1/125)) is wrong, the software thinks the shutter angle is 172 while it is virtually 69 = (24 * (1/125) * 360).

Graffiti

On September 8, 2014 in Blog, Detailed Portfolio

Final composition

Breakdown

Camera Tracking done on handheld D3200. Source 1280 x 720 59.94 fps. White markers applied manually and removed in post production. Deviation 0.5 pixels. Rolling Shutter corrected. Individual videos avaible below.

Main techniques : Camera Tracking, Trackers Removal, Compositing, Color Grading