*Problem Definition* Chart showing resulting file-size depending on JPEG quality and coring index: http://community.elphel.com/files/jpeg-filesize-chart.jpg
Buffer-Monitor is a software that attempts to automatically adjust image compression ratio (JPEG Quality 0-100%) based on the data-rate of the current image stream and the amount/ratio of free/used circular-buffer memory. The goal of the Buffer-Monitor software is to keep JPEG quality at a highest possible value (best image quality) but preventing the buffer from overflowing (dropping frames). The chart above shows that the effects of changing JPEG quality on resulting file-size increase exponentially. Image size is mainly affected by 2 parameters: a. JPEG quality (where the area of primary interest is > 85%) b. actual image content (eg. changing lighting conditions have drastic effects on file-size) So this narrows down the control that Buffer-Monitor has over image quality to basically 15 discrete values. The closer to 100 the value gets the higher the impact of a 1% increase/decrease is on the resulting file-size. I think this is not optimal to ensure continuous high image quality but at the same have time decent room for corrections when reacting to changing image content. *Ideas for Solutions/Improvements* The DCT quantisation table is the only lossy step in JPEG compression and controls which frequency ranges are stored with which accuracy. (higher accuracy -> higher filesize). Higher frequencies are in general reduced stronger. a. Altering DCT quantisation tables to shift focus on higher data-rate/frequency image content. This would mean that lower JPEG quality ranges would have higher frame sizes. Stretching the >85% (X-Axis) area of the above chart over a wider area (0-100%) b. Changing how the JPEG quality value (0-100) affects the DCT quantisation table to achieve the same effect. *Questions* Where are the current quantisation tables stored in the camera and how can they be read/changed? How does JPEG quality affect the quantisation table? Regards Sebastian Credits also go to Oleg for helping understand the topic!
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