Cropping

[Galiven]

Wasn't really sure where to post this question but I figured since we crop using software the PP forum was probably the best place. If this is the wrong place, please forgive me.

My question is probably dirt simple but none of the tutorials I've been able to find (I'm very new to photography) describes cropping techniques. For example, with my XSi, I have a boat load of pixels to work with in each shot. Obviously it is really easy to crop any section of the picture using PP tools like DPP, Picasa, or GIMP. (ie. the tools I currently have available to me)

My problem lies in the size of the area I should use for my crop. Specifically, the ratio of image's dimensions (4x3, etc...). I know that I can crop any area using any ratio to get a 'creative composition' but is there any set image size/ratio I should be keeping as I 'compose' my shot during PP? I know for printing there are specific size's and ratio's but I am not sure exactly what they are.

This also relates to another area of confusion for me. I'm probably going to want to resize the image after the crop. How do you determine a reasonable size? For casual browsing and review I obviously don't want to save a 4K x 2K pixel image (note: I shoot in RAW so I always have the original to go back to) but also don't want to lose picture quality in the conversion process. Which leads to another question: resize then crop, or crop then resize?

Sorry for the newb questions but if anyone has some insight they can provide, or even a link to some suggested reading that would be great. Thanks.

[OsmosisStudios]

Crop, then re-size. Re-size down to 900x600 or 600x400 for web use. Thats usually PLENTY big.

As for cropping, I generally try to stick to print sizes as much as possible. I tend to shoot at 3:2 (the native ratio) and i frame for that size. I often have trouble cropping down to squarer sizes.

[dcclark]

I almost always print at 3:2, which is a good ratio, and is the native ratio of most DSLRs. If you intend to go with portraits, you'll want to crop for 5:4, which would let you print 8x10. That means that you want to compose with about 1/6 of the top (longwise) of your image empty, for cropping.

What size you want to post online is up to you. Osmosis has some good sizes, but my general advice is that it will depend on what you want to do with the photos. If you want people to see details, you'll have to post at least 800x600 -- below that is pretty small, and hard to tell what's really happening in the photo. Flickr's sizing scheme is a good guideline -- their "medium" is a good general target to aim for a "typical" use, whereas I use "large" for a lot of my online postings.

[Galiven]

Thanks for the advice guys. It at least gives me a starting point to work off of. The ratio thing was the biggest tripping point for me.