Display and camera resolution compared
When we convert sensor data to a display, we need to convert the sensor data to match spatial resolution of the display. In this script we define some terms and analyze how the relative resolutions work together.
We assume that a typical sensor acquires information about a scene that is 40 deg of visual angle. Also, we assume that sensor pixels are counted as 'photo-sites', and that these are typically organized into 2x2 arrays as in the Bayer-style pattern.
Copyright ImagEval Consultants, LLC, 2010
Contents
Typical display sizes (see also sensorFormats)
Remember that each display pixel comprises an RGB group of sub-pixels.
HD1080 =[1920,1080]; HD720 = [1280 720]; LCD = [1024 780]; WVGA = [800, 480]; WUXGA = [1920 1200]; WXGA1 = [1280 768]; WXGA2 = [1280 800]; WSXGAP= [1680,1050]; WSVGA = [1020, 600]; XGA = [1024 768]; UXGA = [1600,1200]; QXGA = [2048,1536]; SXGAP = [1400,1050]; SXGA = [1280,1024]; SVGA = [800, 600]; VGA = [640, 480]; CGA = [320, 200]; QVGA = [320, 240]; QQCIF = [72, 88]; QCIF = [144, 176]; QQVGA = [120, 160]; CIF = [288, 352]; MPEG1 = [352 240]; IPHONE = [480 320]; % iPhone YOUTUBE = [560 340]; % YouTube PAL = [768 576]; NTSC = [720 480];
Sensor calculations
We calculate the example of packing each display pixel (RGB) with the data from a single 2x2 Bayer super-pixel in the sensor. This requires no demosaicking. We would just average the two green and shove the values at each super-pixel into a display pixel. (Most people don't think of it this way).
d = ieN2MegaPixel(prod(2*XGA),1); fprintf('2xXGA %.2f\n',d); % Alternatively, if we demosaick the display and sensor pixel % counts are matched. d = ieN2MegaPixel(prod(XGA),1); fprintf('XGA %.2f\n',d); % Now, if we want to render on a small display (iPhone), using a % demosaicked image then we need only d = ieN2MegaPixel(prod(IPHONE),2); fprintf('iPhone %.2f\n',d); % If we have a very large sensor (e.g., 4 Mpix) we reduce the % sensor spatial resolution to only a small percentage of its % natural size to fit everything into an iPhone display. We % define a notion of resolution gain, (rg), to calculate this. % % Specifically, resolution gain (rg) is the reduction in the % megapixel count of the camera needed to fill up the display % % sensorMP*rg = displayMP % % so for a small display (iPhone), assuming demosaicking, we have % a resolution gain sensorMP = 4; d = ieN2MegaPixel(prod(IPHONE),2)/sensorMP; fprintf('sensorMP %d and iPhone %.2f\n',sensorMP, d); % For a big display we have an rg value of d = ieN2MegaPixel(prod(HD1080),2)/sensorMP; fprintf('sensorMP %d and HD1080 %.2f\n',sensorMP, d); % Without demosaicking, just a super-pixel to pixel match, we have d = ieN2MegaPixel(prod(2*IPHONE),2)/sensorMP; fprintf('sensorMP %d and 2*iPhone %.2f\n',sensorMP, d); % For a big display we have an rg value of d = ieN2MegaPixel(prod(2*HD1080),2)/sensorMP; fprintf('sensorMP %d and 2*HD1080 %.2f\n',sensorMP, d); % In the HD1080 case without demosaicking, we need an 8 Mpix camera to % achieve a unit resolution gain sensorMP = 8; ieN2MegaPixel(prod(2*HD1080),2)/sensorMP; fprintf('sensorMP %d and 2*HD1080 %.2f\n',sensorMP,d); % We could calculate things like how much you can zoom an image % for a given display and sensor. You might assume that it is OK % to zoom an image up to the native resolution of the sensor, for % example. Zooming beyond that enters the real of upsampling and % the dreaded image processing world. Eeek. % % You could also consider issues about cropping. % % You can also note that binning means you lose the native % resolution early on, and it can never be retrieved because it % never comes off the sensor. The field of view is preserved (no % cropping) but the spatial resolution is destroyed by the % binning. %
2xXGA 3.10 XGA 0.80 iPhone 0.15 sensorMP 4 and iPhone 0.04 sensorMP 4 and HD1080 0.52 sensorMP 4 and 2*iPhone 0.15 sensorMP 4 and 2*HD1080 2.07 sensorMP 8 and 2*HD1080 2.07