“Camera Obscura” (“Darkened Room”)

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CS 148, Summer 2012 Introduction to Computer Graphics and Imaging

Justin Solomon

http://upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Motion_interpolation_example.jpg/800px-Motion_interpolation_example.jpg

FINAL

APPROACHING

FINAL

APPROACHING

Makeup? Post on Piazza

http://youtu.be/cKrng7ztpog

http://www.mathworks.com/matlabcentral/fx_files/25653/1/Screen_shot_2009_10_26_at_17.54.20.png

Stack of images


Stack of images

x y

t


Stack of images

x y

t

Maintain foreground shape http://en.wikipedia.org/wiki/Seam_carving

http://www.youtube.com/watch?v=3KqiXos1qtw

Find temporally-coherent extensions of image compression

for video.

Find temporally-coherent extensions of image compression

for video.

Codec [koh-dek]:

“Compressor-decompressor;” code for encoding and decoding videos or images.

http://en.wikipedia.org/wiki/Codec

Huge variety of codecs

Different resolution for color http://upload.wikimedia.org/wikipedia/en/0/06/Colorcomp.jpg

Gray plus chroma http://en.wikipedia.org/wiki/YCbCr

Gray plus chroma

Y = 0:299R+ 0:587G+ 0:114B

Cb = 0:564(B ¡ Y ) + 0:5

Cr = 0:713(R¡ Y ) + 0:5

http://voorste.net/tutorials/The.Adobe.Show/Deinterlacing.Video/when.you.get.scaled.interlaced.video.input.jpg

Exploit temporal redundancy http://en.wikipedia.org/wiki/Motion_compensation

Frame

Frame difference

Smaller values!

Exploit temporal redundancy http://en.wikipedia.org/wiki/Motion_compensation

Frame

Frame difference

Smaller values!

Rotate Zoom Translate

code.ucsd.edu/pcosman/253video1.ppt

Frame difference

Compensated difference

Use motion estimate

Divide image into pieces

http://upload.wikimedia.org/wikipedia/commons/b/b1/The_macroblocking_effect_%28JPEG%29.png http://mobileasl.cs.washington.edu/images2/macroblocks.png

Divide image into pieces

http://upload.wikimedia.org/wikipedia/commons/b/b1/The_macroblocking_effect_%28JPEG%29.png http://mobileasl.cs.washington.edu/images2/macroblocks.png

Find source for each target block code.ucsd.edu/pcosman/253video1.ppt



Previous frame

Next frame

Predicted


http://www.youtube.com/watch?v=jFqd-7O7r9g

Prevent drift, data loss http://upload.wikimedia.org/wikipedia/commons/6/64/I_P_and_B_frames.svg

I-frame “Intra-coded picture;” full frame

P-frame “Predicted picture;” difference from I-frame (“delta frame”)

B-frame “Bi-predictive picture;” use nearby I-frames

Typical rates:

30 frames per second 2 I-frames per second

10 P-frames per second Remaining frames are B-frames

Moving Picture Experts Group

Typical rates:

30 frames per second 2 I-frames per second

10 P-frames per second Remaining frames are B-frames

Moving Picture Experts Group

DCT Motion Vector

Motion vector with or without DCT of difference;

DCT can be quantized


Storing motion vector fields

Representation of motion vectors (precision, generality)

Fourier artifacts

Combinatorics of I/P/B frames

Block size, overlap

Coding depth channel for 3D video



Justin Solomon

http://graphics.stanford.edu/courses/cs178-11/

“Camera Obscura” (“Darkened Room”) http://graphics.stanford.edu/courses/cs178/lectures/image-formation-03apr12.pdf



Ray tracing image plane


Ray tracing image plane

One ray of light is not very much.

Fuzzy superposition of images http://www.schoolphysics.co.uk/age11-14/Light/experiments/pinhole_camera/index.html

1

S1+

1

S2=

1

fhttp://en.wikipedia.org/wiki/Lens_%28optics%29

1

S1+

1

S2=

1

fhttp://en.wikipedia.org/wiki/Lens_%28optics%29

http://upload.wikimedia.org/wikipedia/commons/9/92/Spherical_aberration_2.svg

Spherical aberration

http://upload.wikimedia.org/wikipedia/commons/9/92/Spherical_aberration_2.svg

Chromatic aberration

http://graphics.stanford.edu/courses/cs148-11-fall/lectures/camera.pdf

http://graphics.stanford.edu/courses/cs148-10-summer/docs/03_cam_disp_cmpr.pdf

Range of angles captured by sensor

Wide angle lens Telephoto lens

Amount of light reaching sensor

Shutter speed Aperture

http://graphics.stanford.edu/courses/cs148-10-summer/docs/03_cam_disp_cmpr.pdf

Resolution [rez-uh-loo-shuhn]:

Number of pixels in a digital image.

Pixel pitch [pik-suhl pich]:

Density of pixels on a sensor or display.

Maximize contrast Measured in terms of gradients

Phase detection Compare multiple images that should align

http://upload.wikimedia.org/wikipedia/commons/5/5a/Autofocus_phase_detection.svg

Charge-Coupled Device (CCD)

Complementary Metal-Oxide-Semiconductor

(CMOS) http://en.wikipedia.org/wiki/Charge-coupled_device http://cpn.canon-europe.com/files/education/infobank/capturing_the_image/cmos.jpg

Digital cameras have processors that can do simple image processing

before storage.

Color filter array (CFA) http://en.wikipedia.org/wiki/Bayer_filter

Combined M and L cones

during day are most sensitive

to green

Undo Bayer filter pattern http://upload.wikimedia.org/wikipedia/commons/e/e1/Shades_framed_bayer.png

Interpolation (linear or otherwise)

Interpolation (linear or otherwise)

displayed intensity = (maximum intensity)a°

http://www.kenluckephotography.com/portfolio/monitoradjust/files/page17_2.gif

http://upload.wikimedia.org/wikipedia/commons/b/be/Photo_editing_contrast_correction.jpg

http://upload.wikimedia.org/wikipedia/commons/b/be/Photo_editing_contrast_correction.jpg

Looks like a gamma curve!

Histogram equalization http://en.wikipedia.org/wiki/Histogram_equalization

Brighter dark

regions

http://gfoto.tripod.com/phototips/phototips/noise.jpg

http://generalspecialist.com/greenscreen-and-bluescreen-checklist/

I 7! I ¤G+¯(I ¡ I ¤G)

http://www.fotoview.nl/images/usm.jpg http://www.digiretus.com/tippek/photoshop02/sample.jpg

Joint File Interchange Format

1.Optionally convert color spaces 2.Reduce chroma data (usually by 2x) 3.Apply discrete cosine transform to

8x8 blocks 4.Quantize DCT values 5.Store result using lossless encoding

Joint File Interchange Format

1.Optionally convert color spaces 2.Reduce chroma data (usually by 2x) 3.Apply discrete cosine transform to

8x8 blocks 4.Quantize DCT values 5.Store result using lossless encoding

Exchangeable Image File Format

Image format that stores lots of metadata

http://upload.wikimedia.org/wikipedia/commons/6/6a/Konqueror_Exif_data.jpg

“Digital negative”

Store sensor data directly

http://community.futureshop.ca/t5/Tech-Blog/Urban-legends-the-RAW-format/ba-p/155011

RAW JPEG Overexposed

Lots of data to store or process http://ak.buy.com/PI/0/500/232992343.jpg

“Frankencamera” http://graphics.stanford.edu/projects/camera-2.0/images/frankencamera-2.0-2-sshbal.jpg

http://research.microsoft.com/en-us/um/redmond/projects/flashnoflash/flash_no_flash%20%28web%29.pdf

http://upload.wikimedia.org/wikipedia/en/5/53/Image_pipeline2.png



Justin Solomon

http://upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Motion_interpolation_example.jpg/800px-Motion_interpolation_example.jpg http://graphics.stanford.edu/courses/cs178-11/

Documents

“Camera Obscura” (“Darkened Room”)