렌즈와 이미지의 분해능.
해상도란 무엇인가? 그리고 왜 중요한가?
Resolution is the level of detail an image or optical system can distinguish. It is related to sharpness but not identical to it: sharpening raises edge contrast and apparent sharpness without adding resolved detail.
Five different things get called resolution:
- Pixel count resolution, the number of photosites, display elements, or image pixels
- System resolution, the SFR of a whole camera
- Optical resolution, the MTF of the lens on its own
- Angular resolution, the instantaneous field of view one pixel covers
- Effective resolution, a supplier rating that pairs a lens with a sensor class
모든 유형의 해상도는 서로 관련되어 있으며, 컴퓨터 비전에 복합적인 영향을 미칩니다.
왜 결심이 이렇게 혼란스러울 수 있을까?
You're not alone! Even the experts interchangeably use the term "Resolution" when it actually refers to five different quantities, four of them measured and the fifth a rating derived from them. We ran across this misunderstanding between Optical Engineers, Image Quality Engineers, Sensor Engineering, and Computer Vision Engineers during a 2018 conversation within the IEEE P2020 working group.
센서의 해상도는 CMOS 센서 포맷 유형(예: 1/3", 1/2" 등)과도 밀접한 관련이 있으며, 이에 대해서는 별도의 기사에서 다루고 있습니다.
해상도로서의 메가픽셀
화소 수 및 해상도
화소 수로 표시되는 해상도는 휴대폰 업계에 의해 널리 보급되었지만, 50MP 이상의 카메라의 경우 최종 출력물이나 표시되는 이미지의 해상도가 50MP 이상인 경우가 거의 없기 때문에 종종 오해를 불러일으키곤 합니다.
정의:- 센서 내의 빛을 포착하는 포토다이오드 웰의 총 개수.
- 디스플레이 및 프로젝터에 사용되는 발광 소자의 총 개수.
- 디지털 이미지의 총 픽셀 수.
이 카메라의 해상도는 64메가픽셀이며, 12~16메가픽셀 크기의 이미지를 생성합니다.
카메라 해상도는 64MP입니다.
SFR을 해상도로
시스템 해상도란 무엇이며, 왜 중요한가요?
The system resolution can characterize the quality of any digital image. It is frequently used in digital camera production lines to ensure the lens, lens-to-sensor alignment, and image processing pipeline meet a minimum quality threshold. It can also be used to benchmark different cameras and image processing/compression methods. This metric includes inputs from the Lens, the Lens-to-sensor alignment, the Sensor, the ADC, and the Analog+Digital Image Processing Pipeline.
정의:- The Spatial Frequency Response (SFR) measures contrast as a function of spatial frequency, derived from the edge-spread function of a slanted edge (ISO 12233).
Follow ISO 12233 or read Imatest's website.
How to Express System Resolution:State the response threshold the number is read at (MTF50 is common), then the line widths per picture height at that threshold, the field position, and the illumination. SFR is a response curve across spatial frequency, so a single LW/PH figure only has meaning at a stated threshold.
The MTF50 is 2000 LW/PH at 25° field angle under 1000lux 5000K illumination.
이 이미지의 MTF는 2000 LW/PH입니다.
SFR이 컴퓨터 비전에 미치는 영향은 무엇인가?
From: Vasiljevic et al. "Examining the Impact of Blur on Recognition by Convolutional Networks"
MTF를 해상도로
“광학 분해능”은 이미징 광학 엔지니어들이 사용하는 용어로, 시스템 분해능을 산정하는 데 필요한 입력값입니다.
The optical resolution characterizes how much contrast an optical system preserves as detail becomes finer, the measurable basis of perceived sharpness. The MTF applies to both focal and afocal optical systems, including microscopes, imaging lenses, binoculars, and projection optics.
정의:- The Modulation Transfer Function (MTF): the contrast a lens preserves at a stated spatial frequency and field position.
- Two-point criteria such as the Rayleigh criterion answer a different question, the closest separation at which two point sources stay distinguishable, and they do not convert into an MTF percentage.
MTF를 백분율, 주파수, 시야각 및 파장 단위로 기재하십시오.
이 렌즈의 광시야 MTF는 시야각 50°에서 200LP/mm 기준 20%입니다.
이 렌즈의 MTF는 20%입니다.
해상도로 표현된 순간 시야각
“각도 분해능”은 항공우주·방위 산업 분야와 컴퓨터 비전 엔지니어들이 사용합니다.
The Instantaneous Field of View (IFOV) is the angle one pixel covers in object space, so it is quoted per pixel. Pixels per degree is its reciprocal, a sampling density, and on a lens with distortion both figures change with field angle. Neither one is the resolving power of the optics, which is an MTF or Rayleigh question. Pixels per unit distance across an object is a related spatial-sampling figure that only follows once the object range and geometry are fixed.
정의:- IFOV: the angle in object space subtended by one pixel, in degrees, arcminutes, or milliradians per pixel.
- Pixels per degree: the reciprocal of the IFOV expressed in degrees. It is a sampling density, not an angle.
왜곡 프로파일에 대한 각도 분해능이 포함된 당사의 고급 시야각 계산기를 사용해 보세요.
각도 분해능을 표현하는 방법:State which quantity you mean, degrees per pixel or pixels per degree, and give the field angle where it was measured.
The IFOV is 0.083° per pixel at 25° field angle, a sampling density of 12 pixels per degree.
The IFOV is 12 pixels per degree.
각도 분해능이 컴퓨터 비전에 미치는 영향은 무엇인가?
Angular resolution limits the smallest object a network can reliably detect, not the largest. The impact on performance is direct. Dollár et al. show the result on the average miss rate of pedestrian detectors. With less than 50 pixels, even state of the art detectors can have a 50% miss rate on detection. This increases rapidly as scale decreases.
From: Dollár et al. "Pedestrian Detection: An Evaluation of the State of the Art"
메가픽셀과 MTF를 합산한 해상도
“효과적인 해결책”이라는 표현은 렌즈 공급업체의 마케팅 팀에서 사용됩니다.
The effective resolution is a quick method to filter down a lens selection when you are creating a new camera. The optical resolution (MTF) of lenses can be challenging to understand without extensive experience in camera hardware. Many experienced camera engineers do not even know the tricks which manufacturers can play with MTF charts/testing, so effective resolution can be a shortcut directly to system-level resolution.
정의:- 렌즈의 광학 해상도가 적합하다고 여겨지는 센서 픽셀 수 기준 해상도.
화소 수와 이미지 센서 포맷 크기를 모두 포함하십시오.
이 렌즈는 12MP 1/2.3인치 센서에 적합합니다.
The lens is rated for 12MP so its optical resolution is suitable for any 12MP sensor.
이 오해의 소지가 있는 지표는 앞으로도 계속 렌즈 제조사들에 의해 남용될 것입니다. 렌즈를 구매하려는 분이라면, 이제 미리 경고받은 셈입니다.
참고 자료 및 관련 링크
- Dollár et al. "Pedestrian Detection: An Evaluation of the State of the Art"
- Vasiljevic et al. "Examining the Impact of Blur on Recognition by Convolutional Networks"
그렇다면, 커먼랜즈에서는 렌즈에 대해 이야기할 때 ‘해상도’라는 용어를 어떻게 사용하고 있을까요?
As a lens supplier, we base Effective Resolution ratings on empirical System Resolution measurements.
What matters for performance is the final image quality. An ISO 12233 measurement is a whole-camera result: it depends on the sensor's pixel pitch and sampling, the processing pipeline, aperture, focus, field position, and the chart and analysis. We repeat the measurement across sensors with different pixel pitch and state the pairing conditions, so the rating describes the lens on a sensor class rather than a standalone lens constant.
- First, we run through-focus ISO 12233:2014 measurements on a set of sensors whose pixel pitch differs.
- Those measurements also fix the pixel pitch the rating is based on.
- Then we find the maximum image circle diameter the lens delivers.
- Finally, we apply the maximum sensor size and aspect ratio that fits inside that diameter, then calculate the total number of pixels at the limiting pitch.
- We carry that pitch over from the run above rather than measuring anything a second time.
- Then we calculate how many pixels of that pitch fit on a 4:3 sensor of that format type.
높은 유효 해상도를 갖춘 M12 렌즈
Four M12 lenses from the Commonlands catalog. Each is rated for effective resolution using the through-focus ISO 12233:2014 process described above.
카메라 사양을 어떻게 정해야 할지 고민 중이신가요?
당사의 무료 웹 기반 AoV 계산기를 사용하여 시스템에 필요한 시야각(Field of View)을 확인하십시오. 그런 다음 M12 렌즈 계산기를 사용하여 요구 사항에 맞는 렌즈를 찾아보십시오. 또한 당사의 피사계 심도 계산기는 모든 센서 및 렌즈 조합에 대한 초점 거리 및 피사계 심도 정보를 제공합니다.
또한 많은 엔지니어들이 흥미를 느낄 만한 다른 계산기들도 몇 가지 마련되어 있습니다.
