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RAW images
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I’ve just read an interesting article in Personal Computer World about RAW images. I though I’d share an interesting point from it. The sensor responds to light in a linear fashion so RAW images that have blown highlights can be corrected, whereas JPEGs can rarely benefit. Under-exposed RAW files simply do not have the data there, so correcting underexposure creates noise. It’s therefore better to over-expose than to under-expose when working in RAW.
Can I also recommend Picasa? This free program is excellent in the extreme and seems to offer good RAW support (in that it even opens my Pentax PEF files). The first part of my RAW “workflow” (read playflow) is to open Picasa while I copy the memory card to my PC and immediately delete all the crud before I do anything else. It’s fast and it’s easy and you can download it by following the link at
http://www.pete-smith.co.uk/dynamic/photos_tn.php for which Google pay me a few cents in commission!Pete,
With regard to the RAW files, I’ll have to try out the over-exposure myself to see if thats the case.
On Picasa, I found when I was using my D70 that it displayed them with a brown colour cast on them
which was also there when I saved them as jpg. Might just be a Nikon or Nikon D70 NEF file with Picasa issue.Mark
I don’t use it to edit or export images, because I tend to think it’s not going to cut the mustard next to a pro tool like PS. It’s great for quickly viewing, rotating, brightening, cropping and deleting RAW files before moving the good shots to a better editor. The main beauty, to me, is that I know the original image is untouched – even when I’m playing with a client’s JPEGs – this means I can assess the worth of a big bundle of pics without accidentally changing stuff.
PeteTheBloke wrote:
I’ve just read an interesting article in Personal Computer World about RAW images. I though I’d share an interesting point from it. The sensor responds to light in a linear fashion so RAW images that have blown highlights can be corrected, whereas JPEGs can rarely benefit. Under-exposed RAW files simply do not have the data there, so correcting underexposure creates noise. It’s therefore better to over-expose than to under-expose when working in RAW.
Michael Reichmann of the Luminous Landscape has an article on his site for some time now, called Expose (to the) Right in which he goes into detail about this concept. It works well, however, one needs to take care not to overdo it as there still is a risk of blowing the highlights.
It is true that with RAW you have some chance of recovering blown highlights but only up to a point.
The danger if you really push to the right is that you might severely blow only one or two of the channels so it looks fine in the histogram but when you come to adjust (e.g levels or saturation) the blown channels start to behave very strangely.
I would still always use the “expose to the right” technique but I would tend to keep the tail of the histogram back 1/2 a stop from blowing. Even at this I still often get small blown highlights in the red channel which can posterise on adjustment.
Andy
Luckily my 30D shows histograms for each colour channel. Not sure about you thorsten, but for most images I use the red channel as a guide, simply because it is the easiest to blow the highlights on.
SteveD wrote:
Luckily my 30D shows histograms for each colour channel. Not sure about you thorsten, but for most images I use the red channel as a guide, simply because it is the easiest to blow the highlights on.
This was one of the key deciding factors that helped me in my decision to get this camera. So many times with my 10D the luminance histogram looked perfect and it wasn’t until I viewed the image in my RAW converter that I noticed one of the channels (usually the red one) were blown. I now always shoot using the RGB histograms rather than the luminance histogram for this very reason and it has definitely made a difference for the better.
I was at the photvision Roadshow the other day and Guy gowan was talking about this particular subject and said that you could over expose using raw up to a stop and a half max. Once you are in camera raw you can use the exposure slider to bring back the highlights that are blown out,then convert to jpeg and bring back the shadow areas using channels and the curves adjustment.He demonstrated this and it seemed to work extremely well.i’ve yet to try it out myyself though.
I shoot raw almost exclusively and one thing I have noticed is that when the camera display shows blinking highlights (which is an indicator that one has blown the highlights), the raw image doesn’t show any blowout at all and the image is perfectly useable, which tends to be in line with some of the points made above.
Thank you for the link on “Expose “to the right””, Thorsten..It worked for me. I started to shoot raw recently and applied my usual technique to uderexpose a bit for safety. Silly me, it didn’t work for raw. So thanks again for the tip.
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