AP0100CS datasheet(25/73 Pages) ONSEMI

25 / 73 page

AP0100CS/D Rev. 6, Pub. 1/16 EN

©Semiconductor Components Industries, LLC,2016.

AP0100CS HDR: Image Signal Processor (ISP)

Test Patterns

Adaptive Local Tone Mapping (ALTM)

Real world scenes often have very high dynamic range (HDR) that far exceeds the elec-

trical dynamic range of the imager. Dynamic range is defined as the luminance ratio

between the brightest and the darkest object in a scene. In recent years many technolo-

gies have been developed to capture the full dynamic range of real world scenes. For

example, the multiple exposure method is widely adopted for capturing high dynamic

range images, which combines a series of low dynamic range images of the same scene

taken under different exposure times into a single HDR image.

Even though the new digital imaging technology enables the capture of the full dynamic

range, low dynamic range display devices are the limiting factor. Today’s typical LCD

monitor has contrast ratio around 1,000:1; however, it is not typical for an HDR image

(the contrast ratio for an HDR image is around 250,000:1). Therefore, in order to repro-

duce HDR images on a low dynamic range display device, the captured high dynamic

range must be compressed to the available range of the display device. This is commonly

called tone mapping.

Tone mapping methods can be classified into global tone mapping and local tone

mapping. Global tone mapping methods apply the same mapping function to all pixels.

While global tone mapping methods provide computationally simple and easy to use

solutions, they often cause loss of contrast and detail. A local tone mapping is thus

necessary in addition to global tone mapping for the reproduction of visually more

appealing images that also reveal scene details that are important for automotive safety

and surveillance applications. Local tone mapping methods use a spatially variable

mapping function determined by the neighborhood of a pixel, which allows it to

increase the local contrast and the visibility of some details of the image. Local methods

usually yield more pleasing results because they exploit the fact that human vision is

more sensitive to local contrast.

ON Semiconductor’s ALTM solution significantly improves the performance over global

tone mapping. ALTM is directly applied to the Bayer domain to compress the dynamic

range from 20-bit to 12-bit. This allows the regular color pipeline to be used for HDR

image rendering.

Color Interpolation

In the raw data stream fed by the external sensor to the IFP, each pixel is represented by a

20- or 12-bit integer number, which can be considered proportional to the pixel's

response to a one-color light stimulus, red, green, or blue, depending on the pixel's posi-

tion under the color filter array. Initial data processing steps, up to and including ALTM,

preserve the one-color-per-pixel nature of the data stream, but after ALTM it must be

converted to a three-colors-per-pixel stream appropriate for standard color processing.

The conversion is done by an edge-sensitive color interpolation module. The module

pads the incomplete color information available for each pixel with information

extracted from an appropriate set of neighboring pixels. The algorithm used to select

this set and extract the information seeks the best compromise between preserving

edges and filtering out high frequency noise in flat field areas. The edge threshold can be

set through register settings.

AP0100CS データシート(PDF) 25 Page - ON Semiconductor

AP0100CS データシート(HTML) 25 Page - ON Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73

データシートダウンロード