This document discusses challenges with low-end Android device cameras and provides recommendations to optimize image quality and frame rate. It notes that many low-end Android cameras have fixed apertures, so exposure is defined only by ISO and shutter speed. It recommends using the "Sports" scene mode, which locks the frame rate at 30 FPS while sacrificing some ISO, allowing a constant frame rate with acceptable noise in most lighting conditions. The document also discusses auto-focus problems that can cause over- or under-exposure and recommends removing exposure locks manually or using scene modes.

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
2

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
3

4. Exposure Triangle
Exposure
ISO
Shutter speedAperture
Exposure – amount of light per unit area reaching the image sensor
4

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)
18

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