Adaptive generation of Q-table2 for improved image quality
View Patent ↗Brightness correction and image enhancement are derived to compensate for changes in captured image data by hardware scanners and the like by statistically measuring the captured data and generating or selecting a compensation quantization table to be substituted in image data encoded for compression. Three techniques of compensation usable singly or in combination are provided which may be used in combination with techniques for dynamic range reduction for extreme compression. Thus, improved images which may be enhanced in any desired manner, for example, to conform to an established image standard, may be derived from data having sufficient compression to allow economically acceptable long-term storage in high-speed access storage media even though the data captured is degraded in dynamic range, brightness and the like.
1. A method of compressing image data including steps of
capturing image data to derive captured image data,
statistically measuring said captured image data to develop an image data metric,
quantizing and encoding said captured image data to derive encoded and compressed image data, and
substituting a quantization table in accordance with said image data metric or data representing said image data metric into said encoded and compressed image data.
2. A method as recited in claim 1 , including the further step of
compressing dynamic range of said captured image data prior to said step of quantizing and encoding.
3. A method as recited in claim 1 , wherein said step of statistically measuring said captured image data includes a step of
developing a histogram of video values.
4. A method as recited in claim 1 , including the further step of
performing a transform operation on said captured image data.
5. A method as recited in claim 1 , wherein said step of substituting a quantization table includes steps of
developing or selecting a substitute quantization table from said data representing said metric, and
using said substitute quantization table for decoding said image.
6. Apparatus for compressing image data including
a sensor for capturing image data to derive captured image data,
a data processor for statistically measuring said captured image data to develop an image data metric, quantizing and encoding said captured image data to derive encoded and compressed image data, and substituting a quantization table in accordance with said image data metric or data representing said image data metric into said encoded and compressed image data, and
means for storing or transmitting said encoded and compressed image data including at least one of said quantization table and said data representing said metric.
7. Apparatus as recited in claim 6 , further including
means for compressing dynamic range of said captured image data prior to said step of quantizing and encoding.
8. Apparatus as recited in claim 6 , further including
means for decoding and displaying said encoded and compressed image data in accordance with said quantization table substituted into said encoded and compressed image data or a quantization table derived from said metric.