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[ WROCC Home » Meetings » Past Meetings » September 2006 ]

Digital Photography with Barry Thompson

September 2006 meeting – report by Steve Fryatt

September’s meeting featured Barry Thompson of DARC, who had travelled up from Derbyshire to talk about digital photography, RAW files, image manipulation and other related topics. On arriving at the club, members were greeted with a large number of A4 and A3 sized photographic prints, demonstrating both Barry’s skill as a photographer and the quality that can be achieved with a correctly set up computer system.

The meeting was opened by Chris Hughes, who reminded those present that WROCC will be 25 next year and asked for ideas on how to celebrate. Chris also asked for members’ feedback on the future of the charity auction in December – do we want to hold one this year, and if so, what format should it take?

With the announcements out of the way, the meeting moved on to the main event. Barry started by talking about digital cameras themselves, and how to go about selecting one. These days, they come in all shapes and sizes: from simple compact models to advanced digital SLRs. Add to this a bewildering array of lens types and different systems for converting the picture into digital data, and making a decision can be daunting.

The best advice seems to be to consider carefully why the camera is being bought, and what types of photography it will be used for – that is, action shots or still images, close-ups or landscapes? How the resulting images are to be used will determine the number of megapixels (in effect, the resolution) of the image sensor: blowing a photo up to poster size will require more pixels in the original than if it will just be used on a website.

Other areas to consider are lens type (in particular features such as optical zoom), the format of memory card used, and the size, operation and ease of use of the camera. Barry suggested that the last points, in particular, can often best be answered by talking to a local dealer and actually handling the cameras under consideration.

Reviews are also good places to look for information, and Barry suggested looking at photography magazines and websites to see what they have to say about the various models. Sample images from the different cameras posted online can also be a good source of information.

Having dealt with the hardware, we moved on to RAW image files: the ‘native’ format used by many digital cameras to store their images. They are most commonly available on mid- to high-end models, as an alternative to the JPEG and TIFF formats. As the name suggests, RAW files are just the raw, unprocessed data from the image sensor accompanied by information on the date and time of capture and details of the camera settings.

The main advantage of RAW files is that, unlike JPEG, no processing or compression is carried out by the camera before they are saved: this results in more detail being left for post-procesing on a computer at a later stage. While larger than JPEGs, due to the lack of compression, RAW files are significantly smaller than TIFFs.

Before looking at the software available to manipulate RAW files on a PC, Barry went off on a small diversion to discuss the two types of image sensor used in current digital cameras. The sensor is the part of the camera that converts the light coming in through the lens into electrical signals, and is analogous in many ways to the film in a conventional camera.

A sensor consists of a grid of pixels, rather like a monitor in reverse. In the most common type – the striped array sensor – each pixel is only able to detect one of either red, green or blue light. To get around this, the colours are arranged in a matrix and the missing values are interpolated to fill in the gaps. An alternative to the striped array is the Foveon X3 sensor, which are currently only available in the Sigma range of cameras; each pixel can detect red, green and blue light, making the resulting image much more detailed as interpolation is not required.

Editing RAW files can be done with a number of pieces of software. Invariably camera manufacturers will supply their own tools with the camera, and there are a several commercial titles available. As there is no defined standard for RAW data, manufacturer-supplied solutions will be generally be restricted to a specific range of models; commercial alternatives will generally receive the occasional update to take account of any new formats that emerge.

Using RAW files for images provides more flexibility in terms of the post-processing that can be done, due to the additional data that they contain. Manipulating colour balance and adjusting over or under exposure is likely to be more successful with a RAW image than with a JPEG, for example. On the downside, RAW files take up more space than compressed formats, are slower to transfer and process, and require manual adjustments to get the best results.

Finally, Barry went on to look briefly at monitor and printer calibration: a mystical but necessary process if images are to look anything like their screen representation when printed on paper. The simplest (and cheapest) way to calibrate a device is to print a step wedge and check that the component parts are all distinct and visible. On a monitor, this is simply a case of displaying the image and adjusting the brightness and contrast controls until it looks right.

Adobe Photoshop users will find that there are a number of facilities in the software to assist with monitor and printer calibration. Hardware is also available, and Barry showed us the ColorVision Spider: a strange looking object that hangs on to the front of the monitor and measures the colour of the display in conjunction with special software.

Tools to calibrate printers are also available, and range from software to use with a normal scanner to a spectrocolorimeter to accurately measure the colours on a printed page. All of the methods appeared to involve a certain amount of trial and error, but the rewards are in more accurate reproduction of digital images.

The meeting ended with a question and answer session, where topics including the use of special papers for inkjet printing were covered. The evening’s attendance suggested that this was one of our more popular presentations for a while, and afterwards a number of members asked if Barry could return to look at image processing and manipulation in more depth. If this can be arranged, we can look forward to the next instalment with interest.

Previous July 2006
Making Music with MIDI
Home October 2006
Some Impromptu Demonstrations
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