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Thread: How do you measure the size of a crop?

  1. #1
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    Default How do you measure the size of a crop?

    How do you tell when you've cropped an image 20% or 30% etc? I usually look at the original image and take a guess, but I was wondering if there is a more accurate way of telling.

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    Work out the image area in pixels and divide the new area by the original to get the exact percentage.

    Eg 6 megapixels / 8 megapixels should give you a 25% crop.... I think... it's late. I am old and fading into the night of sleep. And got to feed a very young Tawny Frogmouth that fell out of its nest.

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    best way is to calculate linearly divide the long axis pixels (after) by the long axis (before) the crop. So for a 50% crop the height of the bird in the full frame will be half the height in the crop.
    Chris Ross
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    www.aus-natural.com
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    I don't calculate it at all. When I'm done editing the original image in photoshop, I'll select the whole image, copy it, open a new file (which is automatically the same size as the copied area) and then I resize the image or canvas to 60/40/80% or whatever size crop I think would work, then I paste the image on and just shift it around until it fits right within the new boundaries. Then I always know how much I've cropped off. In which case, if you're typing in to resize the image to 60%, you've cropped off 40. So the crop is 40, but the image is 60% of the original.
    Reposts welcome =)

    Blog- Close Encounters of the Bird Kind. Updated 28/05/2014 "Courting Cuckoos"

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    Yes Chris, all sounds easy, but what if you change the height as most people tend to crop from more than one side? Hence why working out the total image area in megapixels, and comparing to the original in megapixels will give the most accurate reduction in size. Some people may not actually believe HOW big a crop they are making when they think they are only cropping a tiny bit.

    In the original size area just enter your camera raw pixel dimensions and the cropped one enter the cropped dimensions BEFORE you resize for web or whatever. Then you can work out the exact number of pixels in your image compared to the original. As you may notice, I am still in the dark ages using an old 8 megapixel camera. Rest assured though that even if I had 100 megapixels my principle of cropping as little as possible, if anything, would apply.

    Cheerio
    Attached Thumbnails Attached Thumbnails crop calculator.JPG  

  6. #6
    Tony Hansford Guest

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    I suppose you refer to it either of two ways depending on how your brain works:

    1. The image is now 40% of what it originally was so you have a 60% crop.
    or
    2. You have thrown away 40% of the image so you now have a 60% crop, meaning it is 60% of original size.

    I tend to use the second option as in seems more natural to me to say the image is now 60% of what it was originally.

    Which is correct?

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    I just "guesstimate". I compare the size of the crop to the overall image and assess what percentile of the original it covers. If it looks close to quarter of a frame then its a 25% crop, half the frame then its 50%. If I crop a full frame image by just a little bit then I estimate it is 85% upwards.
    So my value is the amount of the original RAW image it represents. Not sure if this is how others define a crop value.

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    Ahh, just submitted that and then you got in too Tony
    Yes, I prefer the second option as stated above. Good to hear others define it like that too.

  9. #9
    Tony Hansford Guest

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    I think Bec Z beat us both Paul.

    While on this subject, what in meant by 100% crop? I often see on other forums like POTN people show say a shot of the moon and then after it they have a 100% crop which is bigger or more zoomed in. Using option 1 they would not have any image left, and using option 2 the image would be the original size and not cropped at all.

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    I think when people are saying it's a 100% crop, when it's a more zoomed in version of another image, they mean that they have simply cropped from the original, but the image hasn't been resized. Such as if you were viewing the full size raw image, and then a close up of a certain area of that image that someone is calling 100% crop, they mean that that area of the image (the moon) is the same size as if you were viewing the full-sized raw image. It's more like 100% zoom than 100% crop.

    I also think people sometimes mistakenly use 100% crop when they haven't cropped the image at all, it's simply been resized yet you are viewing 100% of the original image.

    I hope that made sense. It's hard to put into words :P
    Reposts welcome =)

    Blog- Close Encounters of the Bird Kind. Updated 28/05/2014 "Courting Cuckoos"

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    100% crop means you zoom into 100% view. CTRL+1 in Photoshop.

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    Tony
    With referring to 100% crop. See the two images I place into this pane. One shows a full frame image as seen in Photoshop. Note the red arrow showing that the image is shown at 25% of its original size (to fit my laptop window; with bigger screens you can see a bigger image, I have a 15" screen only). To see the most detail you can go into 100% view, note the second image that shows a tighter crop of the bird. The red arrow shows to the little area again, but now the image has been magnified to 100% of its size. Hence why it's often called 100% crop to show the most amount of detail when in question. I always check images at 100% before I proceed with post processing and will only keep the ones I deem sharp enough. Needless to say everyone's definition of sharp enough is different.
    Attached Thumbnails Attached Thumbnails Full-sized-BF.jpg   Full-sized-BF100percent.jpg  

  13. The following user says thank you to Ákos Lumnitzer for their reply:

    Rebecca Zanker (10-10-2011)

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    With regards to how you express it, I always say:
    "image is 60% of original"
    (using 60 as some figure I made up just now
    Familiarity breeds contempt; don't neglect the common birds
    --\\
    ---\\_(j*)>.........Aus Life List: 534 (Northern Royal Albatross - 6/9/14)
    ----\___)................NSW List: 428 (Northern Royal Albatross - 6/9/14)
    ------\ \..............o..2014 List: 348 (Southern Giant Petrel - 6/9/14)

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    Quote Originally Posted by Ákos Lumnitzer View Post
    Yes Chris, all sounds easy, but what if you change the height as most people tend to crop from more than one side? Hence why working out the total image area in megapixels, and comparing to the original in megapixels will give the most accurate reduction in size. Some people may not actually believe HOW big a crop they are making when they think they are only cropping a tiny bit.
    Yes but if you do it linearly as I described the size of the bird in frame doubles in linear dimension with a 50% crop, seems easier to me to work out how the height of the bird varies in relation to the full frame than to deal with areas, you can do it roughly in your head by pixels after/pixels before, picking whichever axis makes most sense, if it's a horizontal cropped to a vertical say so then give the height as a ratio. And when you refer to a crop as 60% of frame refers to having 60% of the original width or height in the crop. referring to how much you discarded leaves it open to confusion I think.
    Chris Ross
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    www.aus-natural.com
    Instagram: @ausnaturalimages

  16. #15
    Tony Hansford Guest

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    Akos, do you then do a printscreen to save it as a 100% crop so you can post it on forums etc?

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