We often get questions from our customers on how to make the most out of Kairos’ services.
Based on our own experiences of building the APIs and developing apps with them, we’ve complied a list of practical tips on best practices.
You can refer to these recommendations to improve the quality and accuracy of the data you capture.
Placement, lighting, and distance recommendations
Position camera so subjects' faces appear vertical in the image. Faces should be closest to the center of the scene. For best results, the camera should be placed in such a way that subjects will be looking directly at the camera. This will allow the measurement of attention and duration.
Avoid pointing the camera at bright lights, the sun or any area with strong backlighting.
The maximum distance the APIs could work at depends on the resolution of the camera and the lens used. For example, for accurate results with the Face Recognition API, the captured image needs to have at least 64 pixels between a subject’s eyes. If you plan to use the APIs for long distances, we recommend that you use a camera with a high megapixel value.
Recommendations for mounted displays and devices
For digital display use cases, the camera should be placed on top or just below the display. Typically, head height (5-6 feet off the ground) is the optimal height placement. The camera should be placed as close to the display’s center in the horizontal direction.
For smart device use cases, the forward facing camera typically appears at the top of the device therefore, optimal height placement is usually a little less than head height (i.e: 5’ 8’’).
If you’re using the APIs for a one-to-one use case such as a time clock app or an app that uses face recognition for authentication, we recommend a flexible mounting so subjects can manually adjust height.
Image Capture (for Face Recognition API only)
Recommendations for positioning, expressions and focus
Face the camera directly and position yourself so that your face fills the frame with 1-2 inch margins on each side.
Maintain a neutral expression, remove any dark glasses or tinted lenses and keep both eyes open.
For increased visibility, avoid bright backlighting and glare by taking your photographs under even light.
Image focus and blur can have similar effects on performance as low resolution so make sure your captured image is not blurry.We do not currently have an objective scale to measure blurriness, so we recommend using common sense to evaluate the blurriness of an image.
If the camera is having difficulty focusing, you might be too close or too far from the device.
On the Go
Recommendations for embedded, forward facing cameras
Subjects should hold the device at a comfortable, stable distance from their face. Typically this is within arms length.
Subjects should tilt the device and adjust their head so as to face towards the screen. It’s similar to ‘taking a selfie’. Onscreen prompts will further guide the subjects into an optimal position.
Recommendations for uploading reference images for the Face Recognition API or capturing videos with the Emotion Analysis API
For Face Recognition API, both JPG and PNG photos may be uploaded. For Emotion Analysis API, MOV, MP4 and FLV videos may be uploaded.
All photos and videos should be rotated such that faces are generally upright without further adjustment.
The accuracy of our APIs depend on the quality of the face template used as reference. For the Face Recognition API, this means the quality of enrolled images. For the Emotion Analysis API, this means how well the subject’s facial features are captured in the beginning of the video.
For example, a video that starts off with the subject close to the camera and ends with the subject being far from the camera will return better results than a video that starts with the subject far from the camera and ends with the subject close to the camera.
For the Face Recognition API, to increase confidence in the system, we recommend enrolling 8-10 different images per user.
Dimension recommendations for optimum results.
There are two factors which affect the usability of an enroled image: absolute face size in pixels and face size relative to the total size of the image. The above diagram and chart depict the minimum requirements for both.
On average, the pixel width between a person’s eyes is half the distance of their head width. There is no minimum image dimension requirement for using Kairos however, we recommend enrolling photographs or capturing videos where there are at least 64 pixels between a subject's two eyes and the head to image width ratio is no less than 1:8.
Under ideal circumstances, images with at least 120 pixels between the eyes should be used. It is generally not necessary to use images with more than 400 pixels between the eyes, although this would not be detrimental to identification performance.