About making pictures   - resolution  by  Waeshael

 

Macro shot with DMC-LC40

a 4MP camera using 1/1.7 inch ccd sensor with Leica Vario-Summicron f2.0- f2.8 with 2 aspheric lenses

resolution


In order to take advantage of the higher “resolution” of the sensor, the lens has to be very, very good. The smaller the sensor and the higher the resolution the better the lens needs to be. The bigger the sensor the bigger the glass diameter has to be. And big pieces of glass with high resolution costs a lot. The Summicron f 2.0, which is designed to cover a sensor 24 mm x 36 mm, is a big lens, made with very rare types of glass,to produce fine images, and this is why it costs $7,000.

Smaller sensors can be covered by lenses of smaller diameter. The 4/3 and micro 4/3 cameras for example have a sensor 17.3 mm x 13mm, and lenses designed for them are less expensive to make. For example: the

Panasonic 25mm f/1.4 Leica DG Summilux Aspherical Lens for Micro 4/3 System costs less than $600.

The differences between micro 4/3 and 4/3 is the dimensions from the lens to the sensor, which is smaller for micro 4/3 and this allows for cheaper lenses. And the mirror and optical finder can be done away with in micro 4/3 cameras which lowers the cost.

Lenses for the Full 4/3 camera are bigger and more expensive. The Full 4/3 DSLR 25mm Lens f1.4 is $1200.

Cameras like the SONY NEX-5 use an APS-C sensor which is 15.6 x 23.5 mm - bigger than 4/3 and requiring lenses with bigger glass. A Sony Carl Zeiss Planar T* 50mm F1.4 ZA Lens for Digital SLT and NEX Cameras costs $1500.

A full frame camera which has a 24 x 36 mm sensor requires bigger lenses (glass diameter) and here Leica lenses come into play, as they are designed for film of the same dimensions. Now we are looking at $7000 50mm lenses.


For those of us posting images to the WEB, for public viewing, there is no need to produce an image that has more pixels than the largest monitor likely to be used by the public. Today that is about 4 MP (2500 x 1600 pixels.) Many picture servers limit the image to something less than this. On the Leicaimages site the maximum dimension is 2000 pixels and the largest file that can be uploaded to the site is 2MB. If you shoot your pictures at 4 MP, and crop them a little, you can post them to the site without any need to scale them. If you also use the highest quality JPEG compression (close to 100%,), and the highest quality color conversion YCC of 4:4:4 then the file will be the highest quality it can be, and it might just squeeze in under the 2MB file size limitation.

Suppose that instead you set the camera to capture images in RAW, which is always made at the highest resolution of the camera, and captured 20 MP of data. After demosaicing and RAW conversion you will have a 60MB TIFF file of 20 MP (5000 x 4000 pixels). This must be scaled to 4MP maximum for the site, which is an odd fraction 1/5 of the original. The editing software must reconstruct an image that consists of only 20% of the original data - i.e 80% of the data must be discarded. The software offers you a choice of scaling algorithms - mine has ten choices, and you must choose the one that does the least harm to the image, for in the process of discarding data, something of the original quality will be lost. Whatever the process chosen the final image can have no more resolution than the 4 MP image from the 4MP camera. And it will probably look less sharp because of the averaging function of the scaling software. You will have to sharpen the scaled down image to make it look right.







Number of photosites and resolution


The more photosites there are in the sensor, the better the chance the camera has of making a good reconstruction that more closely matches the original scene. Any spill over of light from one photosite to the next will produce less blur in the image if there are more photosites.


More photosites is a good thing for photographers doing commercial work for printing. The downside of this is that the software has to deal cleanly with the additional noise introduced by the smaller photosites, which collect less light per photosite. Also the higher the number of photosites the more of the electronics takes away real estate from the light gathering part, because there are more tracks on the surface. To combat these issues, the sensor is made bigger. Bigger sensors are more expensive, and require a lot more tooling to produce. Any failure in the sensor substrate means that a large chunk of the silicon wafer has to be ditched, and this makes what remains more costly/sensor. A new sensor design called BSI recovers some of the real estate used by the electronics, and so increases sensitivity. New developments in sensor design are aimed at producing high count sensors for phones, in order to get a bigger market share. This month an 18 MP phone camera was put into production.


A high number of photosites may not improve the picture resolution, which is dependent on many factors including scene luminance, lens MTF (Modulation transfer function), filter array, demosaicing algorithm, image adjustment in camera (noise reduction, sharpening, film and curves adjustment.), and image magnification.


On the left is a crop (784 x 789 pixels) of a picture originally 2240 x 1680 pixels. You are looking at a 1:1 (100% scale) image by a 4 MP camera at its base ISO.


The detail is good and the picture looks just like my watch. The stainless steel looks like stainless steel. All in all, the picture represents the original object faithfully.

If a higher photosite camera had been used, say, the NEX-5 with 14.2 MP, I cannot imagine that when downsized to fit the web, the image could look any better. None of my prime Leica lenses can do macro work like this.


The DMC-L40, the DMC-LC5, and the Digilux 1, will focus to 6cm from the lens. This is a CCD sensor 1/1.7 inch with CMYG filter array. On sale in 2002. Compare the “resolution” in this image with that of the D-Lux 6 camera on the next page. The camera designs are 10 years apart, yet the image quality is no different, because the D-Lux 6 image had to be scaled to fit the WEB display requirements (in this case to fit this window.)

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