Safe Dual Boot by Hardware Switching

The usual way of implementing a dual-boot system is by software. During the boot sequence the user selects the required operating system from a list. This is fine until one or other of the installed operating systems requires upgrading to a later version. Can we be confident that the dual boot will still work after the upgrade? At the very least we would be advised to backup everything.

There is an alternative which avoids all such worries; instead of switching between operating systems in software, use a hardware switch. Imagine a simple toggle switch on the front of your machine: UP for Ubuntu, DOWN for Windows – select the OS then power up.

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Measuring Monitor Gamma

I have devised a method of measuring gamma without the need for special equipment – a way of setting up a display which is independent of the operating system. Commercial profiling systems don’t seem to provide software for Ubuntu (Linux).

There are several charts and applets on the web which rely on subjectively matching stripes and grey patches but whilst my method uses the same principle the match is based on measured luminance rather than on human judgement.

Gamma measurement

The method uses test targets displayed in Photoshop (or other image/graphics processing application) – which has the advantage of predictable colour management – and hardware costing about £10 (US $16) including the meter!

I have just added a page describing the system. Have a look and feel free to comment.

Test Cards for Monitor checks (2)

Since my previous post and uploading the page on this subject I have noticed that the test cards look different in different browsers. In IE and Chrome the shadow card shows a just perceptible difference between the ‘4’ patch and the ‘0’ background. In Firefox, Seamonkey and Safari there is a more noticeable difference. I believe this is because these last three are implementing colour management and are showing the card ‘correctly’. This was confirmed by viewing the file in Photoshop and selecting either ‘don’t color manage’ or using the embedded profile (sRGB).

I should point out that since the page was originally uploaded I have replaced the jpeg test cards with .png files so as not to confuse matters with embedded profiles. This does not in any way invalidate the above statements but it does mean that to view the files correctly in Photoshop a profile (sRGB) should be assigned and colour management applied on opening. The appearance of the test cards (now without embedded profiles) in the listed browsers is unchanged, suggesting that those browsers implementing colour management are assuming an sRGB profile.

Test Cards for Monitor checks

How often at photographic club meetings do we hear the comment “It doesn’t look like that on my monitor” when an image is projected? Obviously the fault could be with the projection system (i.e. computer and projector) or with the monitor, or both!

If you are serious about producing good quality images for projection or printing, you could start by checking your monitor. I have just published a completely revised technical note including two test cards which will show at a glance whether your system needs adjustment.

Please have a look at this and let me have comments.


Photographic Competitions

There has been much debate amongst amateur photographers, since we “went digital” about just how far we should be allowed to go in producing creative images – where should we draw the line particularly with regard to eligibility for photographic competitions? My thoughts are as follows:

Before I enter my photographs in a photographic competition I should have a clear conscience about two things; that they are my photographs and that they are my photographs.

The first point, relates to authenticity, defined as “Real, actual, genuine; original, first-hand; really proceeding from its stated source, author, painter, etc.” (New Shorter Oxford English Dictionary).

That would appear to be the easy bit. More difficult to answer is the question, in relation to any single image, “Is this a photograph?” (in the sense of “Should it be allowed in a “photographic competition”?”) We might require at least 50% (of the area?) of the image to be photographic. But what about the other 50%? Even if not photographic it must be authentic, i.e. created by the stated author – not plagiarised!

I believe that if we are to produce a set of rules or a code of conduct we should avoid explicit reference to commercial products, particular tools, plug-ins or whatever. It is quite clear that if you use a brush in your post processing that is circular (hard or soft) it is a mathematical entity and does not embody another person’s artwork – if on the other hand it is shaped like a butterfly it should not be allowed, not because it is not a photograph but because it is not yours.

Personally I would similarly not allow the use of textures, whatever the source (built in or plug-in) if they are not yours. Your textures are the ones that you photographed or scanned on a flat-bed scanner. In this context, I have no problem in regarding the output of a scanner as a “photograph”. Problems obviously arise if, for example, you scan a watercolour painting (your own) and enter that in a photographic competition – a digression best avoided.

Whatever rules or guidance we formulate, we should not worry about “policing”. I believe this is often used as an excuse to do nothing. I am sure that I could win medals using some of my wife’s unpublished images; nobody is policing this – my conscience prevents me doing it.

Photography and free software

Today I’m launching my new website. Initially it’s about photography and in particular panoramic photography, but I shall no doubt digress into areas of digital image processing and computing generally as time goes on. As an amateur photographer familiar with Photoshop and Lightroom, I have been looking at alternatives since I first installed Ubuntu 8.04 (Linux) on my 2nd computer in 2008.

After spending some time over the last few years trying Gimp, Cinepaint and Rawtherapee, I have concluded that an unbiassed assessment is very difficult because of the steep learning curve involved. It is said that “You can’t teach an old dog new tricks” but I am no less enthusiastic about the potential of these applications and intend to follow their development further.

I have been very satisfied with the use of entirely free software to produce a stitched panorama.The above pano was produced using Rawtherapee (Raw converter), Hugin (Panorama stitcher) and Cinepaint (Image processor) running on Ubuntu (Operating System). The result is as good as any produced by ‘commercial’ software. The full resolution version (over 30 Megapixels) viewed at 100%, shows no defects.

Incidentally this website looks pretty good on the Midori browser running on my Raspberry Pi – but that’s another story.

Photography by John Widdall

Update 30/07/12: As the new site is substantially complete, I have removed content from the old site and redirected visitors to this one.

((I am gradually migrating my web pages to WordPress. Until this process is complete you may wish to view my old website at

My URL: will now take you to my new site (i.e. this one).