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Author Topic: Croping  (Read 2175 times)
davaglo
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« on: September 18, 2005, 04:28:03 PM »
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Cropping of a photograph is a reduction in size of the photograph.
Does this also reduce the number of pixals in the photograph?
If so, does this limit the ability to resup the photograph to the maximum size, without reducing quality, it could have been before cropping?
In photoshop, should one make a copy of the original photograph and then crop the duplicate?
I use a Canon 20D, I'd also like to know the maximum size I can resup to.
I have a couple of photographs I took from Alaska that I would like to frame. I don't have a printer and the town where I live doesn't have a business that could do the job. Any online suggestions would be appreciated.
Thanks
Jerry
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jrg
howard smith
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« Reply #1 on: September 18, 2005, 05:04:01 PM »
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Does this also reduce the number of pixals in the photograph?

Yes, but it does not change the pixels/inch.  Imagine making an 8x10 print and then chopping it down to a 4x5.   Same stuff in the 4x5 section as was in the 8x10.  Now enlarge the 4x5 back up to 8x10.  It will have less "quality" than the uncropped 8x10.  It would be the same as an uncropped 16x20.

If so, does this limit the ability to resup the photograph to the maximum size, without reducing quality, it could have been before cropping?

Yes. Less information in the crop but spreadf over a larger area.

In photoshop, should one make a copy of the original photograph and then crop the duplicate?

What I have found useful is to copy the original for processing. Then when I screw it up, change my mind, or get some newer software, I can go back and start over fresh.
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jdemott
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« Reply #2 on: September 18, 2005, 07:29:28 PM »
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Quote
I use a Canon 20D, I'd also like to know the maximum size I can resup to.

It depends. Specifically, it depends on your personal preferences, the intended viewing distance of the print, and the subject matter of the photo.

This is a hotly debated topic on which people have strongly held opinions, but there is no clear right or wrong answer. A print that will only be viewed from a distance (a billboard is an extreme example) can be printed at much lower resolutions than one which will be viewed close up. A photo that has a lot of fine detail and depends on a high degree of clarity and sharpness for its visual impact requires high pixel densities for the best prints--many landscape prints fall in this category. Other types of photos, such as candid shots of people, action photos, and street photography, are often somewhat less sharp and detailed anyway, so lower pixel densities are quite acceptable.
The quality of the photo and the quality of the post-processing also make a big difference. A powerful photo that has been skillfully handled in Photoshop can make a great impression even printed as fairly low resolutions.

With all those qualifications, my rules of thumb are as follows. Best quality prints are obtained from files at 360 pixels per inch of original resolution (i.e., not ressed up) and printed with equipment capable of handling that resolution. Pixel densities greater than 360 per inch (of original resolution) don't make a material difference in print quality for normal viewing even at fairly close distances. For a 20D, that means the very best print quality would be at sizes of up to about 6 by 9 inches uncropped. With ressing up, significantly larger print sizes are possible. A 12 by 18 print (four times the area of the 6 by 9) should be acceptable to most people for normal viewing, but the difference in quality when compared with the same size print from a higher resolution camera like the 1DsMk2 would also be apparent to most photographers. Some people report making prints of up to 16 by 24 inches from 6 to 8MP files, but I don't think I would be happy with that for many landscape photos.

So what is the "maximum" size print you can make? Ultimately it depends on what you like. I have some 6MP files that I'm not happy with at 12 by 18 and others that I find okay at that size. If you have a dynamite shot that you're just dying to print at 20 by 30, I 'd say go for it. You'll never know what works for you until you've done some experimenting.  On the other hand, if what you really like is extremely detailed landscapes, then maybe you should try doing some stitched panoramas if you want to make large prints from your 20D.
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John DeMott
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