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01-22-2009, 08:20 PM   #1
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What's the difference between cropping and resizing?

Could someone explain the difference between cropping and resizing a photo? I understand that cropping when you need to get rid of part of a photo. But what is resizing and why do we need to resize a photo?

01-22-2009, 08:23 PM   #2
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you got cropping right, but resizing keeps all aspects of the photo intact, just makes it smaller in size or resolution, for web or print...
01-23-2009, 02:01 AM   #3
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Why resize ?

The answer depends on what you want to do with your image.

If you want to send someone a picture by email, or post on a web forum such as this, a jpeg image looks its best when viewed at 100% size, as this is the setting you should use for your final sharpening of the image. Now a 10mp camera image will be roughly 2600x 3900 pixels. Given that most computer screens are set to a resolutions like1024x768 or 1280x1024, you cannot view the image at 100% and fit it all on the screen. So you should downsize the image in post-processing to 1000 or 800 pixels on the longest side.

If you want to make a large print of your picture, you need to follow a different set of rules where the physical size of the image is important. This depends not only on pixel WxH , but also pixels per inch.

Do some research to understand more about it. This is a good place to start Digital Photography Tutorials
01-23-2009, 12:43 PM   #4
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Look here

QuoteOriginally posted by luckyduck Quote
Could someone explain the difference between cropping and resizing a photo? I understand that cropping when you need to get rid of part of a photo. But what is resizing and why do we need to resize a photo?
https://www.pentaxforums.com/forums/general-pentax-photography/45890-lost-term-cropping.html

01-23-2009, 05:20 PM   #5
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QuoteOriginally posted by pschlute Quote

Do some research to understand more about it. This is a good place to start Digital Photography Tutorials
Great link. I found it very helpful. Thanks.
01-23-2009, 07:22 PM   #6
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QuoteOriginally posted by luckyduck Quote
Could someone explain the difference between cropping and resizing a photo? I understand that cropping when you need to get rid of part of a photo. But what is resizing and why do we need to resize a photo?
You would resize a picture to match the way you wish to display it....

A native 10MP camera image is 3872 X 2592 pixels.

However even a high res screen will only have 1600X1400 pixels or so, so you cannot display the picture at 100%. Most image viewing software has a "zoom" function which effectively resizes the viewed image to fit the screen (though the native image is not affected).

But, if you want to display the image on a website, you will generally need to make it smaller (downsizing) so it can be displayed on the screen at 100%. Generally I downsize to 900X600 pixels for pBase. This also means the image is smaller, so I can upload it more easily. Effectively this is just like zooming only its permanent - the image processing software has "zoomed" the actual file by (simplistically) looking at groups of pixels and replacing them with a single pixel of the average RGB value of the ones it replaces. Note - I have not cropped the image, because the view is the same.

Now, if you want to print a photo then most printers can print far more dots per inch than you get on a screen, so you do not normally need to resize. The printer driver will usually decide how many dots per inch (DPI) to print in order to squeeze the native picture within your paper size. For a 12 X 8" print you need to fit 3872 pixels into 12 inches which is 323 dots per inch borderless. If you want a border, up it to 350dpi for a nice 1/2" border. Note the image is still 3872 X 2592 pixels. I have just changed the output resolution. Note - some print software forces you to do this manually but its a simple calculation.

If you want to print 24 X16" prints, then the resolution is simply halved to 175 DPI. This is OK for normal viewing distances but you would not want to go much lower (or bigger). If you do you will start to see pixelation or jaggy edges. If you want to print larger then you can resize the image upwards! So called upsizing/uprezzing is just downsizing in reverse but in this case the computer fills in (interpolates) new pixels by looking at the pixels around them. You dont get more detail, but it does look smoother if you print really big.
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