| 摘要 |
<p>A method and apparatus for reading bar codes or other images while reducing the need for self-generated illumination. An image reader (1501) comprises an optical collection system (1509), an aperture (1508) with a high aspect ratio and/or a multi-focal lens(es). An optically transmissive spacer affixed to the front of the handheld unit, and a diffuser may also be used to reflect ambient light from the handheld unit to provide additional illumination at close range. A masked CCD detector receives collected light and is coupled to an adaptive exposure circuit. A correlated double sampling circuit coupled to the adaptive exposure circuit rejects common mode noise. The correlated double sampling circuit is connected to a signal processor which uses a derivative based technique for detecting edges of the image, to decode the encoded information from the image.</p> |
