Noise in Digital Camera Raw Files – How to Measure it

After writing two articles on the Nature of Light and its relevance to digital photography, I found that the subject of noise still fascinated me and decided that I had to make some measurements. Looking at the wiggly waveforms of my previous article might indicate that camera A is noisier than camera B but can we measure the noise in a rigorous way? This present article explains how to do that using free software. As well as presenting graphs of the measurements I have attempted to explain the results from physical principles – and evidently the noise is predominantly photon noise (aka shot noise).Selection_026

Click here to read the article

Posted in Photography, technology | Tagged , , , , , , , ,

Test Cards for Monitor Adjustment – Revised

Test Cards - 1Test Cards - 2Calibration and Profiling

I have updated the page on this subject in order to clarify the distinction between calibration and profiling (or characterisation), and to remove reference to commercial operating systems now obsolete.

To avoid confusion I have now included only a version of each test card with sRGB profiles assigned and saved as jpegs. These should be viewed in an application that is colour aware (i.e. one that recognises and uses the embedded profile).

Click here for Test Cards page

Posted in Computers, Photography | Tagged , , , ,

How the Nature of Light affects the performance of digital cameras — (Part 2) Noise

ImageJ-G9

G9, pixel plot across sample

In the second of two articles I look at another natural phenomenon, photon noise (also known as Shot noise). As with diffraction blur, the problem becomes more serious as the physical size of the sensor is reduced.
Whilst this is not the only source of noise, it is now the dominant one in the darker areas of an image where only a relatively small number of photons are incident on the sensor. It is the counting of photons, which is subject to Poisson statistics, which produces the noise.

Click here to read the article

Click here to read the first article: Diffraction blur

Posted in Photography, technology | Tagged , , , , | Leave a comment

How the Nature of Light affects the performance of digital cameras — A new Technical Note

G9-f8-2.38

Image of a point source: Blue = Intensity, Red = Sensor output. Computer model of G9 at f/8

Reducing the physical size of a camera, even if the total number of pixels is maintained, inevitably reduces the quality of the images because of two fundamental properties of light itself. This technical article looks at diffraction, usually explained by considering light as waves. A future article will look at photon noise, explained by considering light as particles.
A simple rule-of-thumb is established for determining the “diffraction limited f-number” by relating this to pixel pitch on the sensor.
The earlier, pre-digital, criterion for diffraction limited aperture (based on required print sharpness) is revisited and considered to be still valid – perhaps with a little sharpening.

Click here to read the article

Posted in Photography | Tagged , , , , ,

Test Cards for Monitor Adjustment – An Update

Test Cards - 1Test Cards - 2Basic adjustment of monitors and projection systems

When I last updated my page on this subject (2012) I decided that it was best to offer the test cards as .png files and leave it to the user to assign a profile (presumably sRGB) and to view the result in an application such as Photoshop. For convenience, I have now added a version of each test card with sRGB profiles assigned and saved as jpegs. These should be viewed in an application that is colour aware (i.e. one that recognises and uses the embedded profile).

Click here for Test Cards page

Posted in Computers, Photography | Tagged , , | Leave a comment

Raw Processors: Which Demosaicing Method? (Part 2)

Further Thoughts on Demosaicing Methods in Free Open Source Raw Processors

I suggested in Part 1 that I would also compare the performance of different demosaicing methods on noisy images. I now believe that this would be impractical as any simple comparison could give misleading results and any meaningful comparison would be very time-consuming.

The basic problem is that there are too many variables, and these variables are not well defined. Read more

Posted in Computers, Photography | Tagged , , , | 2 Comments

Raw Processors: Which Demosaicing Method? (Part1)

Comparison of Demosaicing Methods available in Free, Open Source Raw Processors

My previous article included a table listing the various demosaicing algorithms offered by the four raw processors considered and I wondered why we (as users) needed such a wide choice. The table is reproduced below.DemosaicI decided to investigate those offered by RawTherapee by looking closely at the detail in an image of tree branches against the sky – the same part of the same raw file processed by each of the algorithms. Read more

Posted in Computers, Photography | Tagged , , , , , | 4 Comments