1. Processing The Latent Image
DMI 50B
Kyle Thornton

2. Hand Processing
Films were immersed in tanks containing processing chemicals for a period of time
The chemicals had to be mixed and stirred by hand
The total time was about an hour from developer to drying
Occasionally, a film was read right out of the developer
Thus the term wet read

3. Automatic Processing
The first automatic processor still immersed film in tanks
Films were hung, and a conveyor did the rest of the work
It could process about 120 films/hour
Total time was about 40 minutes
Eventually, the roller transport system was invented
This is what is used today in automatic processors

4. Automated Processing 1940’s Style

5. An Updated Version

6. Advantages Of Automatic Processing
Saves time and manpower
Processing time is reduced to 90 seconds
The variability in results caused by hand-dunking is eliminated
Radiographs are available in minutes
There is no variance in temperature
Allows standardization of techniques
Overall, efficiency is improved

7. Converting the Latent Image to a Manifest Image
Step I
Formation of the latent image by exposing the silver-halide grains to x-radiation
Step II
Development of only the exposed grains by reducing agents
Step III
Removal of the unexposed grains and making the image permanent by fixing

8. Latent Image Formation

9. The Sequence Of Processing Steps
Wetting
Loosens the emulsion to allow penetration of developing chemicals
Development
The stage in which the latent image is converted to a manifest image
Stop Bath
An acid solution to stop the development process

10. The Sequence Of Processing Steps
Fixing
Removes any silver halide crystals that were not exposed to radiation or light
Washing
Removes any chemicals not rinsed off in the previous steps
Drying
Removes any water, prepares the film for handling, storage, and viewing

11. Sequence of Processing Steps

12. Wetting Solution Water
This is the solvent for all processing chemicals
A solvent is what solids and powders are mixed into
In automatic processing, this step is combined with development

13. Development The developer solution is a reducing agent
It reduces the silver ions of exposed crystals to metallic silver
The main development agent is hydroquinone
Rapidly produces shades of gray
The other developing agent phenidone
Produces black tones slowly

14. The Effect of Development Upon Silver Halide Crystals
Exposure and Reduction
Of Silver Halide Crystals
Underdevelopment v. Overdevelopment

15. Developer Chemicals and Their Functions

16. Fixing
The stop bath is combined with fixing in the automatic processor
Fixing stops the developing process and makes the manifest image permanent
The activator that neutralizes any residual developer is acetic acid
The other fixing agents remove any unexposed or undeveloped silver-halide crystals

17. Fixing Agents And Their Purpose

18. Hypo Retention
Occurs when fixing solution (thiosulfate or hypo) is not rinsed sufficiently
This will cause a processed film to discolor over time
This is caused by oxidation of the fixing agent
The result is a discolored film of poor quality
This means that the wash cycle is not working properly

19. Washing The agent in the washing cycle is water
The film is rinsed to remove any chemical residue
Water is continuously cycled through the wash tank to ensure that it remains clean
Poor washing can result in hypo retention or other chemical artifacts

20. Drying The final step of the processing cycle
Hot air is blown over the film to dry it
The dryer stage works independently of the processing stages

21. Safety Developer chemicals are caustic and can cause chemical burns
It will stain fabric permanently
If chemicals are splashed on skin, or in eyes, rinse immediately, and seek treatment
Protective eyewear, and aprons should be worn if mixing chemicals

22. Processor Anatomy Transport System Temperature Control System
Circulation System
Replenishment System
Dryer System
Electrical System

23. Processor Anatomy

24. Transport System
A series of rollers moving in precision convey the film through each stage of development at precise intervals
Begins at the feed tray
A microswitch is placed here that detects the size film and controls replenishment
The transport system consists of three subsystems

25. Subsystems
Rollers
1 inch diameter rollers that convey the film through the processor
Transport racks
All of the rollers are positioned on a rack assembly
At each bend there is a curved metal lip called a guideshoe to properly position the film for turning
Drive subsystem
Supplied by a motor
Drives the rollers and a series of gears, belts, and pulleys

26. Transport System Components

27. Temperature Control System
Temperature, time, and chemical concentration control development
Optimum temperature is app. 95 degrees F
The temperature is monitored by a thermostat
This controls a heating element in the developer tank

28. Circulation System
Continuously agitates the processing chemicals ensuring that they are properly mixed
Water is continuously circulated through the processor

29. Replenishment System
Monitors film activity and replenishes the solutions as needed
This prevents oxidation of the solutions in the processor
A microswitch at the feeding tray monitors film size and regulates appropriate replenishment

30. Feeding Tray

31. Dryer System
A blower sucks in room air and blows it across a heating element in order to dry film
This also serves as exhaust for the automatic processor

32. Electrical System Supplies power to the processor
Each electrical component of the processor has its own wiring and fuses

33. Rapid Processing Reduces processing time to about 30 seconds
The chemicals are more concentrated
Fixer and developer temperatures are higher
Rapid processing is very useful in surgery, and emergency where time is valuable

34. Extended Processing Used in mammography Allows for lower patient dose
Film is in the developer longer
Processing time if about 3 minutes
Contrast is improved

35. Daylight processing A processor is still used
The means of loading cassettes and putting films is different
The daylight system allows automatic loading of cassettes for use
Also automatically unloads them into the processor
Eliminates time in the darkroom

36. Daylight Processing Unit

37. Dry Processing Does not use any wet chemicals
Two techniques for dry processing
Photothermography
Laser light prints image
Formed on silver halide
Image developed by heat
Thermography
Uses a heat source (print head)
Heat creates the image in organic silver salts
Photothermography renders more accurate detail
Thermography can look pixely, and dust can accumulate between print head and film