1. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Traditional Imaging Imaging Science Fundamentals

2. Chester F. Carlson Center for Imaging Science

3. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science

4. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science “Grain” of Film and Paper u Electron Photomicrographs of Emulsion Grains

5. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science What is Silver Halide? Silver (Ag) Halide group

6. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Structure of a Typical B&W Film u Film base u Plastic u Antihalation backing u Prevents light from reflecting back. u Emulsion Silver Halide Crystals Suspended in gelatin, like fruits in Jell-O™!

7. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Exposed AgX Crystals u When a silver halide crystal is exposed to light, some of the AgX molecules break up into their constituents, one of which is metallic silver (“pure” Ag). Exposure After Exposure

8. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Silver Halide Process Chain u A latent image is formed after exposure (invisible to human eye). u After processing, the latent image is turned into a visible, stable image. ExposureProcessing DevelopStopFix Latent Image Visible (Stable) Image

9. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Processing Photographic Film u Developer “amplifies” the atomic silver to visible silver strands. u Stop Bath stops the development process. u Fix dissolves the unexposed AgX crystals, making the film safe to expose to light. u Wash with water to rinse fix chemicals away.

10. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Silver Halide Grains

11. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Light from a Point Source u A point source is a source in which the light appears to be emanating from one point in space. u A point source casts energy in all directions, shown above as rays. *

12. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Point Source Casting Rays u Take a look at 7 of the rays cast from one position (the tip) of the object. u With no collection element, all of these rays fall on the “image plane.” There is no way to determine the source of the rays. Object

13. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Three Points on the Object u This becomes a problem when three points on the object are considered. u The energy can be collected at the image plane, but all information about the object is lost.

14. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Need for Collection Element A crucial element in most imaging systems is the component responsible for collecting the energy emerging from a given point on the object, such that it is brought to a single point in the image.

15. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Ideal Pinhole Camera An ideal pinhole allows only a single ray from each point on the object to pass through. This preserves the spatial distribution of energy, creating a sharp image. An ideal pinhole camera has an infinitely small aperture (opening).

16. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Realistic Pinhole Camera Since the pinhole cannot be infinitely small, more than one ray actually gets through, blurring the image formed at the image plane.

17. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Capture u The image can now be captured using a detection system, such as photographic film. u Film must be processed to yield a permanent, visible image.

18. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Limitations of Pinhole Camera u Finite pinhole size and diffraction degrade final image. u Light collection is poor - aperture must be small - so image acquisition is slow.

19. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Image Formation For a camera to be efficient, the pinhole is replaced by a lens. The lens redirects light rays emanating from the object.

20. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Why does processed film look “negative”? u Silver strands formed by exposure of photographic film to light actually appear dark (they are NOT shiny). u So, where light hits the film during exposure, it turns darker.

21. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science What determines how dark film becomes? u THE GRAINS! u Size u Shape u Chemical composition u Distribution

22. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science “Grain” of Film and Paper u Electron Photomicrographs of Emulsion Grains u ( n.b. Measurement Bars indicate scale)

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24. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Photographic Finishing u In order to get a “positive” final print, the negative must be projected onto photographic paper. u Negative * negative = positive! u 2 basic “finishing” methods: CONTACT and ENLARGEMENT/REDUCTION

25. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Contact Printing Light Negative Photographic Paper A CONTACT print: The negative is in direct contact with the photographic paper --essentially creating a shadow-gram.

26. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Enlarger / Reducer Light Negative Photographic Paper Optics are used to produce an image of the negative on photographic paper.

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29. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Typical imaging chain for pinhole camera Visible light source Object Dark box pinhole Film (capture) processing Image

30. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Problems with Ideal Pinhole Camera u An infinitely small aperture allows an infinitely small amount of light (zero) to pass through. u Diffraction (which is ignored in geometric optics) blurs the image when the pinhole is very small.

31. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Latent Image Formation (Ex.: shadowgram) Group of AgX Crystals Mask (object) prevents AgX crystals underneath to be exposed. “Unmasked” AgX is exposed to photons. Exposed crystals have different material property (I.e. some AgX bonds have been broken).

32. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Latent Image Formation (with optics) Group of AgX Crystals Optics used to image object onto the film. Illuminated AgX is exposed to photons; but not all AgX is illuminated. Exposed crystals have a different material property.

33. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Contact Printing vs. Enlarger u No loss of signal by the optics. u No reduction in resolution. u Simpler system. u Fixed image size. u Flexible image size. u Some loss in resolution due to enlargement. u Additional optics may degrade final image quality. u Again, flexibility! Contact Printing Enlarger

34. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science What determines how dark film becomes? u Consider the so-called “D-Log H” curve. u Describes how film responds to light: u Density (D) is how dark the film is. u Log H is the exposure (H) in logarithmic scale. Log H D More Exposure Less Exposure Lighter Darker

35. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science D-Log H Curve and Contrast Log H D D More contrast Less contrast Film response Image