What camera?

General cycling advice ( NOT technical ! )
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patricktaylor
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Postby patricktaylor » 9 Feb 2009, 11:10pm

Tom Richardson wrote:... jpegs are 'lossy' - they dump information to make the files smaller. They do that every time that you edit and save them ...

I've read that too. I don't believe it's true - at least not every time you edit and save them, unless you also compress the image. 'Compressing' images for the web (to reduce file size and download time) reduces the number of colours - imperceptibly if done correctly - but this does not happen if an image is saved without further compression. A jpeg image can be saved over and over again without any loss of quality. If you save a jpeg image a thousand times, the file size - an indication of the number of colours - remains the same, so there is no loss.

Of course there are many ways to destroy a jpeg image by editing it!

stewartpratt
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Postby stewartpratt » 9 Feb 2009, 11:58pm

patricktaylor wrote:'Compressing' images for the web (to reduce file size and download time) reduces the number of colours - imperceptibly if done correctly - but this does not happen if an image is saved without further compression. A jpeg image can be saved over and over again without any loss of quality. If you save a jpeg image a thousand times, the file size - an indication of the number of colours - remains the same, so there is no loss.


That's not true. JPEG compression does not reduce the number of colours. And there are many factors affecting a JPEG's file size, including its compression setting and the image data itself (an image with lots of fine detail will be much larger than one with gradual changes in tone and hue). For nearly all modifications to an image, unless you use lossless JPEG mode (and most software and hardware won't use this by default) the image quality deteriorates with editing and saving.

And I'd dispute your point about software making up for a poor camera. It simply won't. Yes, you can modify colours and exposure, but both effectively reduce the gamut and dynamic range you're working with as well as usually increasing noise. And it won't correct poor focus - yes, you can 'sharpen' the image but that's really not the same thing and has other very noticeable side-effects. Realistically, you can't add information that the camera hasn't recorded, you can't unburn the burnt-out bits and you can't unpick details that it's blurred into each other.

That said... Looking on Flickr at some of the output from that BenQ (or at least the DC740) it looks to kick out images far better than anyone has any right to expect for £40. I was expecting it to produce junk llke most cheap digitals, but I'm impressed - almost tempted to get one as an MTB camera except it looks a bit chunky.

emergency_pants
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Postby emergency_pants » 10 Feb 2009, 12:39am

I'm a digital media producer, so if anyone wants the lowdown on some of that stuff, give me a shout. I won't go into one here. :shock: :lol:

My experience is that you can fine tune an image with software, especially if it's taken in RAW mode, which is like a digital version of a film negative. You can take quite ordinary images and make them really lovely. So long as the source image is good quality.

Life, vividness, richness, depth... all these things can't be injected into a photo by software. Those qualities come from what happens to the light travelling through the lens, how effective the sensor is at recording that light, and what the camera does with that information once it's been recorded.

It's really soul-sapping having to run through bad quality images trying to inject some life into them. It's really no good taking an image with a poor piece of kit because you are on the back foot, trying to compensate all the way through the publishing process. :cry:

I still think that BenQ camera looks good value. Be aware though... some of the cheaper cameras produce bad quality images in low light conditions.

pete75
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Postby pete75 » 10 Feb 2009, 7:52am

IN spite of all the electronics in modern camera lens quality is still very important. Amongts Japanese cameras Sony and Panasonic have the best lenses. Sony use Zeiss lenses and Panasonic use Leica lenses whereas the rest use ones of their own design.

brianleach
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Postby brianleach » 10 Feb 2009, 8:26am

I had a similar experience recently. I transferred a number of jpegs to my computer and then viewed and saved each one with a different name.

No other changes were made by me but the file size reduced on average by a third.

When I just changed the name in the directory the file size remained unchanged.

I have never noticed this before but will certainly keep an eye on it in the future.

Does anyone have a simple explanation?

Brian

pigman
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Postby pigman » 10 Feb 2009, 8:30am

Ive just bought a compact camera. I was told by someone who knows a bit about it to avoid AA/AAA batteries cos they dont hold their charge well and you end up needing to carry spare batteries. Unfortunately once you go for Li compact batteries, you jump over the £50 mark. In the end I got one of these, but not at £78. It cost me £62 from boots who are treating them as NOS and are selling off. Your boots store might still have some.

http://www.argos.co.uk/static/Product/p ... 109607.htm

iaincullen
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Postby iaincullen » 10 Feb 2009, 8:37am

Worth considering is the Nikon P50. It's cheap - £79 on Amazon at the moment. Has a viewfinder. The 28mm wide end of the zoom is more useful for many situations than typical compact zooms starting at 35mm or so.

It's not a recent model (hence the price) but got decent reviews for a budget compact camera when it was introduced.

"it's a reasonably well specified camera at a good price that will consistently produce pleasant results with minimal user input."

As per

www.dpreview.com/reviews/nikonp50/page12.asp

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ncutler
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Postby ncutler » 10 Feb 2009, 8:45am

I think that once you realise that you can totally ignore the fashion-victim mega-pixel race there are bargains to be had.

I recently bought a Practica DCZ 4.4 new for less than £30. We lend it to people so that they can record local events for our village website. The thing is perfectly adequate.

My wife still uses a Canon Ixus 400. It's years old, has 4 MB and a tiny screen. There is nothing wrong with its pictures, particularly the out of doors 'touristy' ones. I'd expect to be able to buy a used one for virtually nothing.

I'd echo the usefulness of a viewfinder. Not so much for battery life, but because most LCD screens are vitually useless in bright sunlight.

N

stewartpratt
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Postby stewartpratt » 10 Feb 2009, 8:53am

brianleach wrote:Does anyone have a simple explanation?


Yes.

When an image is saved in JPEG format, the process of encoding it involves compression. The level of compression which is applied can be set - images can be strongly compressed to save space or weakly compressed to retain quality. When you saved, whatever application you were using would have been using a higher compression level than whatever originally saved the images. You'll have also lost image quality in the process (zoom in around the edge of an area of constant colour - eg where trees meet blue sky - and you should see the artifacts). Some applications will give you the option to set the compression when saving JPEGs.

When you rename a file, the actual content of the file is unchanged.

mr bajokoses
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Postby mr bajokoses » 10 Feb 2009, 8:58am

I second the recommendation for the Pentax Optio WP, and its successors. I have the WP 5MP version, and it's an excellent snapshooter. Not up to digital SLR picture quality, but very acceptable in good light, and fantastic for extreme close-up shots - it truly excels here. It's waterproof (submersible) and this is a great fun feature on holiday - take it into the pool or the sea. Being extremely portable, it's ideal for use on a bike ride, and the non-protuding lens means it is less vulnerable to damage.

I understand the BenQ models are based on Pentax hardware (sensors and lenses), which would explain the excellent quality/price ratio.

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Postby pigman » 10 Feb 2009, 9:25am

mr bajokoses wrote:I second the recommendation for the Pentax Optio WP, and its successors.


I should think so! £184 on amazon (unless Ive got confused). A bit over Si's budget methinks.

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patricktaylor
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Postby patricktaylor » 10 Feb 2009, 9:59am

ImageImage

The first jpeg image above has been saved once. The second has been saved 150 times and is not lossy compared to the first. This is demonstrated by the enlargements of each below - the pixels are exactly the same.

ImageImage

The following image is the original, compressed down to 10%, and next to it is an enlargement. The image quality is reduced because it contains less colours, causing it to lose some smoothness in the transitions. The software has also selected different colours in places, because it doesn't have as many to choose from.

ImageImage

stewartpratt
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Postby stewartpratt » 10 Feb 2009, 10:15am

patricktaylor wrote:The first jpeg image above has been saved once. The second has been saved 150 times and is not lossy compared to the first.


Indeed. But (ignoring the fact that you may be using lossless compression) that's re-saving the same image, which isn't a normal scenario. There's no point re-saving it unless you've edited it. In which case you will, gradually, lose quality.

patricktaylor wrote:The image quality is reduced because it contains less colours, causing it to lose some smoothness in the transitions. The software has also selected different colours in places, because it doesn't have as many to choose from.


You've got cause and effect the wrong way round. It contains fewer colours because of the way the compression algorithm works - it causes a smearing effect. There is no reduction in either the number or gamut of colour values available.

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patricktaylor
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Postby patricktaylor » 10 Feb 2009, 10:37am

stewartpratt wrote:... that's re-saving the same image, which isn't a normal scenario. There's no point re-saving it unless you've edited it. In which case you will, gradually, lose quality ...

I was demonstrating that saving a jpeg over and over again in itself does not degrade the quality of the image (contrary to what a lot of people seem to think). As for editing an image, it depends on what is being done to it. Again, editing an image in itself does not degrade it.

... It contains fewer colours because of the way the compression algorithm works - it causes a smearing effect. There is no reduction in either the number or gamut of colour values available ...

I'm not sure what you mean there. You're saying the compressed image does contain fewer colours. A compressed image contains less information, so what information can it lose other than colour? (assuming the number of pixels is the same)

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patricktaylor
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Postby patricktaylor » 10 Feb 2009, 10:58am

stewartpratt wrote:... I'd dispute your point about software making up for a poor camera ...

Why? I frequently receive poor quality images for putting on the web. Typically, they have washed-out sections, dark corners, poor colour or contrast - stuff like that - and they are often not sharp. With a bit of editing they can be much improved.
Last edited by patricktaylor on 10 Feb 2009, 11:01am, edited 1 time in total.