Summary:High-resolution (64MP) and standard-resolution (16MP) images from the Olympus OM-D E-M5 II are compared. The high-resolution images have substantially more fine detail “information” than do the standard-resolution images. That is demonstrably true even when the high-resolution images are down-sampled to 16MP for 1:1 comparison with the standard images. The Olympus high-resolution images are also compared to images from a Sigma DP2 Merrill (14.75MP). Images from both cameras were resampled to dimensions appropriate for making 18-inch-long prints. When viewed on-screen at 100% magnification, the E-M5 II images were clearly superior to the DP2M images. However, when printed, the DP2M images exhibited greater apparent detail. Much of the difference in detail rendition in these comparisons is qualitative rather than quantitative. The E-M5 II high-resolution mode appears to offer considerable advantage if the images are intended for display at large sizes. That advantage must be balanced against the fact that it is appropriate only for tripod shooting of motionless subjects, and the fact that the improved detail is not apparent when images are sized for typical viewing on a computer display.
Summary: The high definition shooting mode of the Olympus OM-D E-M5 Mark II is investigated by simulation of line-pair images. The half-photosite shift that is employed to produce 64MP images from a 16MP sensor can, in principle, double the linear resolution that is otherwise achieved by the camera without sensor shifting. However, image pixels obtained at the shifted sensor position are not independent of pixels obtained at the unshifted position: the two sets of pixels overlap completely, with a half-photosite offset. The result is that micro contrast is reduced in comparison with a true doubling of the linear photosite resolution. Given the 3.73 µm photosite pitch of the E-M5 II sensor, the resolution benefits of sensor shifting decrease rapidly at apertures smaller than about f/5.6 because any potential gain in resolution is overwhelmed by diffraction blur (coupled with non-independence of shifted and un-shifted image pixels).
Summary: The maximum amount of detail that can be contained in an ink-jet print is set by the native resolution of the printer and the size of the print. In the case of the Epson Stylus Pro 3880, maximum detail requires that the image be printed at 720 pixels per inch (ppi). Printing at 720 ppi ensures that the visible detail in the print will be oversampled, and therefore printed with greater sharpness than if the image were captured with fewer pixels and printed to the same size at 360 ppi. In order to fully exploit the capabilities of the Epson 3880 in a modestly large (~ 50 cm) print, it is necessary to have an image on the order of 110 – 120MP. At present, the only way to make maximum-detail prints larger than 25-30 cm, is by stitching multiple frames to make larger images.
Summary: Resolution limits (lp/mm) for a perfect lens as a function of aperture and sensor photosite size are determined by simulation. Results are shown for 20, 50, and 80% line-pair contrast ratios. Smaller photosites always increase resolution and contrast (within the range of sizes and aperture values simulated), although marginal gains are small if diffraction blur is appreciably larger than photosite size. If diffraction blur diameter is reduced to less than photosite size, resolution can improve substantially, particularly when line-pair contrast is high. With respect to “total” resolution (LW/PH), the usual rules of “camera equivalence” are obeyed. The result is that, with perfect lenses, larger sensors can achieve higher total resolution than smaller ones only if they have more photosites (or if depth of field is sacrificed). Resolution limits for a perfect lens are compared to published test results for the Nikkor 85mm f/1.4G on a Nikon D3x, and for the Zeiss Otus 55mm f/1.4 on a Nikon D800E. Test results for the two lens/camera combinations are inconsistent with each other and with simulations, even at smaller apertures where diffraction rather than lens performance is assumed to limit resolution. Reasons for the inconsistencies are discussed. Given that resolution limits depend upon both diffraction blur and photosite size, it is generally not useful to erect a dichotomy between “diffraction-limited” and “sensor-limited” resolution.
Summary: The effect of diffraction blur on resolution of black and white line-pair images is modeled by aggregation of a large number of blur circles. The contrast ratio of the line-pairs declines to 50% when the blur circle diameter is about 79% of the width of a line-pair. Contrast falls to about 7% when the blur circle diameter reaches 115% of the line-pair width. These results imply aperture-specific diffraction-limited resolutions. For example, with 50% contrast, the theoretical limit of image resolution is approximately 209 line-pairs per millimeter (lp/mm) at f/4. No other sources of blur are considered. Results are compared to calculated aperture-specific resolution limits published elsewhere. Resolutions obtained here by simulation are less than those calculated from “standard” formulas when line-pair contrast is 50% or less. However, in the case of high contrast (80%), simulated resolution limits are greater than values obtained by formulas. In order for cameras with “full-frame”, APS-C, and m4/3 sensors to achieve resolutions closer to the theoretical diffraction limits, it will be necessary to increase the number of sensor photosites several-fold. It is not clear how much, if any, improvement will be required in lenses.
Summary: The Gorman-Holbert black and white conversion is discussed with reference to Gorman’s instructions for creating a Photoshop action. The conversion is based on the lightness channel of the L*a*b* color model. As such, it appears to be particularly useful for images with limited color palettes. The conversion also employs the Photoshop High Pass filter as a “finishing” step. The principal effect of the High Pass filter in this application appears to be to increase contrast, which enhances image detail, particularly in the mid tones. The High Pass filter is compared to the Clarity adjustment of Adobe Camera Raw/Lightroom, and to the Unsharp Mask filter that is also available in Photoshop. Two simple modifications to the Gorman-Holbert conversion are suggested. The first substitutes a Gradient Map adjustment layer to enable true split toning. The second implements the High Pass filter as a smart filter so that its radius setting can be easily adjusted.
Summary: Matched pictures were taken with a Nikon D90 and a Nikon D7100. Both images were upsampled for printing at 20 x 13.3 inches (51 x 34 cm) and 360 pixels per inch (ppi) on an Epson Stylus Pro 3880. PhotoZoom Pro 6 (BenVista, Ltd.) was used for upsampling. The resulting prints from the two cameras were nearly indistinguishable with respect to amount and quality of fine detail. As a “control”, prints were also made with upsampling left in the background, under the control of the printer driver or Lightroom. The resulting prints were quite good, but noticeably lower-quality than those made from images upsampled with PhotoZoom Pro. The “native” resolution of the D90 image at 20 x 13.3 inches is only 214 ppi. These results argue that the frequently cited 300-pixel-per-inch rule for high quality ink jet printing is overly conservative when using current software and hardware.
Summary: A camera sensor samples the image that is produced by the lens. The sampling frequency is determined by the photosite pitch of the sensor. In the hypothetical case where a lens is producing images of black and white line-pairs without blur, it is shown that the sampling frequency must be at least four photosites per line-pair in order to recover both the frequency and original contrast of the line-pairs. That is twice the Nyquist sampling rate. Higher sampling frequencies more faithfully reproduce the image formed by the lens. In the case of line-pairs of a given frequency, the edges of the lines become sharper with higher frequency sampling. Published resolution data for the Zeiss 55mm f/1.4 Otus lens on the Nikon D800E are discussed with regard to theoretical limits based on sampling frequency. A case is made that resolution is sensor-limited in that test.
Summary: The Sigma DP3 Merrill is compared to the Nikon D7100 with Nikkor AF-S 50mm f/1.8G lens. A comparison is shown for a matched pair of images that were taken a few minutes apart with the same ISO and aperture, and from the same tripod location. Detail rendition is clearly superior in the DP3M image, even though it was up-sized from its native resolution of 14.75 MP to 24 MP for comparison with the D7100 image. Comparisons are shown for both color and monochrome versions of the test images. Differences in resolution are mitigated somewhat by conversion to monochrome. A second matched pair of images shows that differences between cameras are affected by subject matter.