In the Dynamic Range section of our DSLR reviews we usually look at something that we call ‘RAW headroom’. The RAW headroom could probably be described as the highlight and shadow detail that has been captured in the RAW data but gets lost when a camera’s internal software applies a tone-curve to the RAW image data.

As a rule cameras apply a typical 'S' shaped tone curve to JPEGs to give a visually appealing contrast without harsh clipping of the brightest or darkest tones (the 'shoulders' of the S curve provide a more gentle roll-off than a straight line would). The tone curve applied is often quite steep, sacrificing the tones at the the extremes of highlight and shadow in the pursuit of 'punchy', consumer-friendly out-of-camera results. At the shadow end this is rarely a problem (the very darkest tones are mapped to black, which isn't visually unpleasant and helps reduce noise), but at the highlight end it can mean that what should be a very pale blue sky turns white, or that highlights have harsh edges instead of a gentle gradient. There's no way to get back detail that the camera's tone curve left out of a JPEG, but it is possible to tweak more out of a raw file. Having access to the sensor's full dynamic range also means that you can fix mild under or over exposure by reaching into the headroom.

And so it's very useful to understand what raw headroom is and how you can make use of it to get the maximum out of your images. We regularly receive questions regarding this particular section of our reviews via our feedback system and in the forums, so I thought it would be a good idea to provide some detail about the dpreview approach to raw headroom in a blog article. This isn't a deeply technical post; it's more of a primer on what we do, and why you need to know about the dynamic range hidden away in your raw files.

It's long been obvious that the existing dpr review format - even in its seriously truncated 'concise' form - is unsuitable for the majority of what can be broadly termed 'point and shoot' compact cameras, and I've been wanting to develop a group test format for some time now. There are simply too many compact cameras released each year for us to keep up with (even the most basic camera takes a minimum of a week to put through our battery of tests and to produce a gallery), and the truth is that image quality amongst competing models doesn't - for the most part - vary that much. But there are always going to be exceptions, cameras with image quality that falls well below or rises way above the mean, and unless we test a far higher proportion of the models on the market there's a risk we'll miss these occasional stars and lemons. The group test format may not give you as much detail about the individual cameras, but it does give you a much better idea of the relative quality of a far greater number of competing models.

There has been much contention recently that we're being unfair on high megapixel cameras which show higher levels of noise than lower megapixel cameras. The almost universal argument is that "you can downsample the high megapixel image to reduce noise". This statement is often made with no evidence or example, this article is intended to provide some examples so that you can make your own mind up.

Starting work at dpreview.com is an odd affair. Not only does writing for the web entail many more people reading your work (and scrutinising and criticising it), it also means learning to write for a very different audience: an International one...

We have a brand new blog which desperately needs some content before it can be launched and following our recent Canon EOS 50D review there has been quite a lot of discussion in the forums about the use of Adobe ACR as a RAW converter in our reviews. These, I thought, were two good reasons to get into blogging mode and write a brief article that explains why Dpreview is using ACR and not proprietary or other third party converters for its tests.