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![Digital images
Digital images width
520
j=1
i=1
Intensity : [0,255]
im[176][201] has
value 164
im[194][203] has
value 37
500
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![Exercise
Exercise
• An image’s dimension is 5184 [pixel] x 3888 [pixel]
• The sensor size is 6.17mm x 4.55 mm
• What is the pixel size in mm or micron](https://image.slidesharecdn.com/2-camera-properties-240213064022-eb174586/85/2-Camera-Properties-pdf-15-320.jpg)
2-Camera-Properties.pdf
- 1. Camera properties Panu Srestasathiern,PhD. Researcher Geo-Informatics and Space Technology Development Agency (Public Organization) Camera properties
- 2. Image formation Image formation- - Recap Recap • The geometry of imaging system pixel coordinate system x world coordinate system camera coordinate system (R,T) image coordinate system x1
- 3. Interior orientation Interior orientation •Interior orientation is the metric characteristics of cameras. • It is used to convert pixel coordinates to coordinates in camera space coordinate system.
- 4. Pinhole camera Pinhole camera •Pinhole camera is a simple model to approximate imaging process, perspective projection. If we treat pinhole as a point, only one ray from any given point can enter the camera.
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- 6. • Is thiscamera suitable?
- 7. The reason forlenses The reason for lenses Lenses gather and focus light, allowing for brighter images. for brighter images.
- 8. The reason forlenses The reason for lenses • A lens focuses parallel rays onto a single focal point • Gather more light, while keeping focus; make pinhole perspective projection practical
- 9. Camera Geometry Camera Geometry •The aperture allows light to enter the camera • The image plane is where the image is formed • The focal length is the distance between the aperture and the image plane • The optical axis passes through the center of the aperture and is perpendicular to it.
- 10. Perspective projection equations Perspectiveprojection equations • 3D world mapped to 2D projection in image plane Image plane Focal length Scene / world points Len Forsyth and Ponce Camera coordinate system Optical axis
- 11. Image digitization Image digitization •Image sensor – Complimentary Metal-Oxide Semiconductor (CMOS) – Charge-Coupled Device (CCD)
- 12. Image digitization Image digitization •Sampling means measuring the value of an image at a finite number of points. • Quantization is the representation of the measured value at the sampled point by an integer.
- 13. Digital images Digital images Thinkof images as matrices taken from CCD array.
- 14. Digital images Digital imageswidth 520 j=1 i=1 Intensity : [0,255] im[176][201] has value 164 im[194][203] has value 37 500 height
- 15. Exercise Exercise • An image’sdimension is 5184 [pixel] x 3888 [pixel] • The sensor size is 6.17mm x 4.55 mm • What is the pixel size in mm or micron
- 16. Exercise Exercise • What isthe pixel size of the Sony Alpha NEX-5T at max resolution HINT: https://www.dpreview.com/ HINT: https://www.dpreview.com/
- 17. Focus and depthof field Focus and depth of field • Depth of field: distance between image planes where blur is tolerable • How does the aperture affect the depth of field? • A smaller aperture increases the range in which the object is approximately in focus approximately in focus
- 18. Focus and depthof field Focus and depth of field
- 19. Field of viewdepends on focal length Field of view depends on focal length • As f gets smaller, image becomes more wide angle –more world points project onto the finite image plane • As f gets larger, image becomes more telescopic –smaller part of the world projects onto the finite image plane
- 20. Field of viewdepends on focal length Field of view depends on focal length Smaller FOV = larger Focal Length
- 21. Imaging sensors: recordingthe image Imaging sensors: recording the image • Flash memory: fixed or removable solid state storage device • Storage format: – TIFF : uncompressed – JPEG : compressed at various quality settings Example Example TIFF JPEG JPEG (Hi quality) (med quality) 640x280 pixels 1.0 MB 300 KB 90KB
- 22. Common Lens RelatedIssues Common Lens Related Issues - - Summary Summary Compound (Thick) Lens Vignetting thickness principal planes nodal points α α 1 L 2 L 3 L B A more light from A than B ! Chromatic Abberation Radial and Tangential Distortion R F B F G F Lens has different refractive indices for different wavelengths. image plane ideal actual ideal actual
- 23. Lens Glare Lens Glare •Stray interreflections of light within the optical lens system. • Happens when very bright sources are present in the scene.
- 24. Vignetting Vignetting • Vignetting isthe result of light rays not making it through the entire lens system to the sensor, due to being blocked by the edges of individual lens elements or mechanical stops. • Vignetting is most often seen at or in lower f/#s, short focal length lenses, or lenses where higher resolutions need to be length lenses, or lenses where higher resolutions need to be achieved at a lower cost.
- 25. Vignetting Vignetting • light raysare clipped by the edges of the lens
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- 27. Chromatic aberration Chromatic aberration •As the refractive index of a transmittive medium is dependent on the wavelenght of light, dispersion occurs, when white light transmits such a medium. • Refraction is stronger for light of short wavelengths, for example blue, and less intensive for light of long wavelngths, example blue, and less intensive for light of long wavelngths, for example red.
- 28. Chromatic aberration Chromatic aberration •There are two main types of chromatic aberrations: – The LATERAL (or transverse) chromatic aberration. – The LONGITUDINAL chromatic aberration.
- 29. Chromatic aberration Chromatic aberration •LONGITUDINAL CHROMATIC ABERRATION • There is longitudinal chromatic aberration, if a lens cannot focus different colors in the same focal plane. • It is caused by straight incident light. • The foci of the different colors lie at different points in the • The foci of the different colors lie at different points in the longitudinal direction along the optical axis.
- 30. Chromatic aberration Chromatic aberration •LONGITUDINAL CHROMATIC ABERRATION The longitidinal chromatic aberration leads to colored areas in the images, that arise, because not all three colors can be displayed in focus. Longitudinal chromatic aberration is an error of focus
- 31. Chromatic aberration Chromatic aberration •LATERAL CHROMATIC ABERRATION • Obliquely incident light leads to lateral chromatic aberration. • In that case all colors are in focus in the same plane, but the foci are not placed along the optical axis. Lateral chromatic aberration is an error of magnification
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- 33. Geometric Lens Distortions GeometricLens Distortions • Ideally, a photograph should be a perfect pers-pective mapping of the photographed scene. • For example, the image of a straight line must be straight.
- 34. Geometric Lens Distortions GeometricLens Distortions • Radial distortion Radial lens distortion is the symmetric distortion caused by the lens due to imperfections in curvature when the lens was ground. The distortion appear in radial direction. The distortion appear in radial direction. In other words, the image’s scale changes moving from the center of the field to the edges, leading to straight lines curving either towards the center or towards the edges.
- 35. Geometric Lens Distortions GeometricLens Distortions • Radial distortion Ideally, the image of circle is circle.
- 36. Geometric Lens Distortions GeometricLens Distortions • Radial distortion No Distortion Barrel Distortion Pincushion Distortion (Positive distortion) (Negative distortion)
- 37. Geometric Lens Distortions GeometricLens Distortions • Radial distortion In barrel distortion, image magnification decreases with distance from the optical axis. In pincushion distortion, image magnification increases with the distance from the optical axis. the distance from the optical axis. The wide-angle lenses (or rather zoom lenses when set to short focal length) typically produce a pronounced barrel distortion.
- 38. Geometric Lens Distortions GeometricLens Distortions • Tangential distortion Tangential distortion occurs when the lens and the image plane are not parallel. The tangential distortion coefficients model this type of distortion.
- 39. Geometric Lens Distortions GeometricLens Distortions • Tangential distortion Tangential distortion is perpendicular to radial direction.
- 40. Correcting radial distortion Correctingradial distortion from Helmut Dersch
- 41. Geometric lens distortions Geometriclens distortions • Mathematical model of radial and tangential distortion • How to get these parameters? Camera calibration
- 42. Camera calibration Camera calibration •Simple method for off-the-shelf camera – Use images of calibration pattern
- 43. • Spatial Resolutionis the minimum distance between two adjacent features or the minimum size of a feature, that can be detected by a remote sensing system. (www.geocomm.com) • Spatial Resolution is not simply ground sample distance What is Spatial Resolution? What is Spatial Resolution? • Spatial Resolution is not simply ground sample distance – Also depends on how well a system is focused • Point Spread Function (PSF) 43
- 44. Point Spread Function(PSF) Point Spread Function (PSF) • Image of a point source
- 45. Point Spread Function(PSF) Point Spread Function (PSF)
- 46. Point Spread Function(PSF) Point Spread Function (PSF) • Image of a point source
- 47. Image Formation ExampleI Image Formation Example I
- 48. Image Formation ExampleII Image Formation Example II
- 49. Relation between aperturesize and Airy disk Relation between aperture size and Airy disk • Diffraction Increases as the Imaging Lens Iris is Closed (f/A Increases where A is the aperture size)
- 50. Relation between aperturesize and Airy disk Relation between aperture size and Airy disk • Mathematical formula:
- 51. A real experiment Areal experiment • Canon EOS Rebel 8 Megapixel Camera Max resolution 3456 x 2304 CMOS Bayer Array Manual mode Raw data Raw data Pixel size 6.3 micron
- 52. High Spatial ResolutionData High Spatial Resolution Data Measured building GSD = 1.2 cm 52
- 53. Image Variation withGSD Image Variation with GSD GSD = 4.8 cm GSD = 12 cm GSD = 18 cm
- 54. Image variation withaperture size Image variation with aperture size Increase aperture size GSD = 4.8 cm
- 55. Optimal aperture size Optimalaperture size • The diameter of Airy disk should less than the pixel size. • That is, the main lobe of Airy disk should be in a single pixel. Average visible wavelength is approx. 540 micrometer.
- 56. Optimal aperture size Optimalaperture size • Exercise: …..
- 57. Radiometric characteristics Radiometric characteristics •Important preprocessing step for many vision and graphics algorithms • Use a color chart with precisely known reflectances.
- 58. Radiometric characteristics Radiometric characteristics •Use more camera exposures to fill up the curve. • Method assumes constant lighting on all patches and works best when source is far away (example sunlight). • Unique inverse exists because g is monotonic and smooth for all cameras. all cameras.
- 59.