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maintaining resolution when croping a photo

Posted on 2011-10-16
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Last Modified: 2013-11-19
i have a high res graduation photo which i open in mspaint, and then just crop the part of the photo that is required, and then save that part alone.. as save it again.. but this time the resolution is lost.. (how i can say it the picture came down from 2mb to 200k)

how can you crop a part of the picture and still save in hi-res?
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Question by:25112
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by:Dave Baldwin
Dave Baldwin earned 600 total points
ID: 36977116
You are getting rid of pixels when you crop a photo.  You won't have the same size when you are done.  Technically, 'resolution' is the number of pixels per inch and the image left after cropping still has that 'resolution'.  What it doesn't have is the same size or total number of pixels.  While you could enlarge the remaining part back to the size of the original picture, the results are usually not good because you lose info by cropping.
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hdhondt earned 1400 total points
ID: 36977176
A photo consists of a number of pixels. Modern cameras typically have 6 million (3000 x 2000) or more pixels. The number of pixels in a scan depends on the size of the area you scan, and the scan resolution. If you scan a 6" x 4" photo at 300 dpi you will have 1800 x 1200 pixels.

If you crop the photo you will lose the pixels you did not select. For example, if you select a 3" by 2" area from the 6" x 4" photo, the number of pixels drops to a quarter of the original. There is nothing you can do to really improve that. Software like PhotoShop will let you increase the number of pixels by interpolation, but that can never create new data in the photo.

The next issue is the file format. When the photo is saved as a JPEG, information is lost. The amount of loss depends on the JPEG compression settings. With Paint you cannot change the settings, but PhotoShop can. If Paint uses higher compression than the original, your file size will drop even if you don't change the number of pixels. You also need to be aware that with JPEG you lose more information each time you save the photo: the compressed photo is compressed again when you save. Formats like TIFF or BMP do not have that problem.

BTW, for things like this I normally use IrfanView. It's free and does a much better job at managing images than Paint. It does let you crop, change resolution, change the JPEG compression and much more. Get it from:

http://www.irfanview.com/
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by:25112
ID: 36995210
thanks a lot
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