Short introduction about the functionality of the Android camera on low-end devices.

1. Low-end Android Cameras and the
Exposure Triangle
Martin Cerman

2. • Approx. 45% of Android devices are running ICS or Jelly
Bean (Versions 4.0.3 to 4.3)
• Partially very bad cameras on low-end devices
• Low resolution
• Auto focus problems
• Not completely standardized camera settings
• Exposure locking
• Bad FPS priorities
• Real-time image processing
• => We need the best possible image quality at highest
possible frame-rate
Motivation
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3. 1. Take picture and process it offline
• Provides higher quality images (separate preview and capture settings)
• More callback options (shutter callback, raw picture callback,…)
• Take picture and forget, or switch view and process
2. Get byte array from onPreviewFrame from Camera.PreviewCallback
• Lower quality images (WYSIWYG)
• Only a single callback function
• Provides constant stream of images with variable FPS
Image Capturing
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4. Exposure Triangle
Exposure
ISO
Shutter speedAperture
Exposure – amount of light per unit area reaching the image sensor
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5. Aperture
• A hole or an opening through which light travels
• Defines from what angle and how much light reaches the sensor
• Influences Depth of Field
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6. Aperture – Depth of Field
Small aperture - f/32 Large aperture - f/5.6
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7. Aperture – Depth of Field
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8. Shutter Speed
• Length of time the image sensor is exposed to light
• Depends on opening size of mechanical shutter
• Influences motion blur
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9. Shutter Speed
9*video on the next slide

10. Shutter Speed
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11. ISO
• Measure of a photographic film’s sensitivity to light
• Describes also sensitivity of a camera sensor
• Influences noise in the image
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12. ISO
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13. Exposure Triangle Revisited
• Low-end Android cameras have a fixed aperture!
• Exposure is thus defined only by ISO and shutter speed
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14. Camera Priority Modes
• Good DSLR cameras allow to set all factors manually or define a priority
1. Shutter priority – S mode
2. Aperture priority – A mode
3. Less common Sensitivity Priority or “ISO Priority” – Sv mode
• Low-end Android cameras use by default “ISO Priority” with lowest possible ISO
for less noisy images => lower FPS 14

15. Low ISO, Slow Shutter Speed
15*video on the next slide

16. High ISO, Fast Shutter Speed
16*video on the next slide

17. Android Settings
• Android has “Auto” mode or “Scene” modes
• Auto mode permits change of ISO settings, but supports shutter speed very poorly
• Scene modes have set ISO and shutter speed settings
• Scene modes cannot be obtained by manually changing settings in auto mode
• Android has “ISO priority” mode
• Solution: use “Sports” scene mode
• Has locked 30 FPS
• Sacrifices ISO in favor of constant FPS, while noise is acceptable in most lighting conditions
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18. Auto-focus Problems
• Some devices lock the exposure after focusing
• Lock needs to be removed manually or lock is removed when camera cannot focus
• Causes Over-/Under-exposure when switching between well and badly lit scenes
• Two solutions at the moment:
1) 2)
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19. Auto-focus Problems – Over-exposure
19*video on the next slide

20. Auto-focus Problems – Under-exposure
20*video on the next slide

21. Thank you!
Martin Cerman