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Thread started 26 Feb 2018 (Monday) 08:21
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50%, 100%, 75% crop

 
Ltdave
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Feb 26, 2018 08:21 |  #1

before someone gets snarky and says "google is your friend" i already visited there...

can someone explain how they get a "50% crop" on an image? or a 100% crop?

i can ASSUME that a 50% is using about half of the actual frame for the "finished" size but not really sure how they come up with an exact value of how much is cropped out, or how you actually make a 100% crop...




  
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Post edited 3 months ago by TeamSpeed.
     
Feb 26, 2018 08:29 |  #2

If you use your photo viewing tool, and zoom to a particular level, like 50%, then crop out what is currently on the screen, that is a 50% crop.

Or more mathematically, look at the resolution of the height and width, and crop out enough to get to you 50% of the resolution initially. This is a bit more difficult or tedious at least.


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patrick ­ j
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Feb 26, 2018 08:47 |  #3

Ltdave wrote in post #18572506 (external link)
before someone gets snarky and says "google is your friend" i already visited there...

can someone explain how they get a "50% crop" on an image? or a 100% crop?

i can ASSUME that a 50% is using about half of the actual frame for the "finished" size but not really sure how they come up with an exact value of how much is cropped out, or how you actually make a 100% crop...

I had the same question about the 100 percent crop thing for years, it never made sense, and I think it's deceptive term, but if I have it right, when someone posts a photo and says it's a 100 percent crop, it means that the image is small enough to show at actual size on a computer screen, rather than reduced resolution.


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TeamSpeed
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Post edited 3 months ago by TeamSpeed. (5 edits in all)
     
Feb 26, 2018 08:55 |  #4

patrick j wrote in post #18572534 (external link)
I had the same question about the 100 percent crop thing for years, it never made sense, and I think it's deceptive term, but if I have it right, when someone posts a photo and says it's a 100 percent crop, it means that the image is small enough to show at actual size on a computer screen, rather than reduced resolution.

One must recognize that not all monitors are created equal. On my screen, I can view at 100% and crop out that image. It might be 1000x500 when I am done, and that almost fits my screen. Somebody with a 4K display will see this as a small image, but it is still 100% as long as whatever is used to view the image is showing one to one (file pixel to screen pixel).

When somebody does a 100% crop, they are usually saving the viewing public from the tediousness of taking the full image and viewing it at 100%, then moving it around to the content in question, by cropping out just a section to be concentrated on. Also, many sites don't allow full resolution images to be attached or uploaded.

But again that 100% resulting image may look different on one monitor to another, both due to quality of the monitor and the resolution it is set to for the overall screen.

http://www.mdavid.com.​au/photography/100crop​.shtml (external link)

Anything less than a 100% crop usually means you are cutting out more of the image content, but then resizing down accordingly to get the result to fit for web viewing or printing a certain print size.


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Left ­ Handed ­ Brisket
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Post edited 3 months ago by Left Handed Brisket.
     
Feb 26, 2018 09:02 |  #5

There is nothing deceptive about a 100 percent crop, at all. If anything, a gaggle of photographers will always default to the nerdiest, most specific definition.

If one exports an image to the web as jpg, it will be shown at 72 ppi, unless the HTML makes it different. In general, stretching or shrinking via HTML is bad form. So in that sense, all images are shown at 100 percent.

If on selects a small portion of an image, copies it, then creates a new photoshop file, that new file will retain the pixel dimensions of the copied portion. If you save for web/jpg the result will again be a file that shows up at 100 percent.

The problem arises when someone tries to post a file that is larger than a forum allows. At that point most forum servers will remove extra pixels to make the overall size conform to forum specs.

So as far as web viewing is concerned, if you never throw out (or add) pixels, and the forum software doesn't throw out pixels, you have a 100 percent crop.


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kmilo
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Post edited 3 months ago by kmilo.
     
Feb 26, 2018 09:12 |  #6

My original image is 6000x4000 pixels.

6000 times 4000 equals 24,000,000 total pixels

A 50% crop would leave you with 12,000,000 total pixels .... roughly 4250x2867

Even if you resize that 4250x2867 crop to something like 600x400 ... you're still showing a 50% crop of the original.


... or someone needs to teach me this principle as well :)

edit to add: When someone says 100% crop, they mean the displayed 600x400 pixels is exactly equal to the crop of the original ... it's not resized.


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Left ­ Handed ­ Brisket
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Feb 26, 2018 09:21 |  #7

kmilo wrote in post #18572547 (external link)
My original image is 6000x4000 pixels.

6000 times 4000 equals 24,000,000 total pixels

A 50% crop would leave you with 12,000,000 total pixels .... roughly 4250x2867

Even if you resize that 4250x2867 crop to something like 600x400 ... you're still showing a 50% crop of the original.


... or someone needs to teach me this principle as well :)

This is getting to the real point. 100 percent crop/viewing is used as THE baseline to judge image sharpness, regardless of whether the overall area being viewed is the full image capture or not.

Any thing like 50 percent or whatever other than 100 percent is generally used to convey the amount of the original image that remains. It is not useful for judging image sharpness.

This is where the confusion lies ... the goals of "100 percent crop" vs anything/everything else are really very different.


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Post edited 3 months ago by agedbriar.
     
Feb 26, 2018 10:33 |  #8

Posting "a 100% crop" (usually for some technical evaluation of the picture) means taking a small section of the picture, a section small enough to be viewed without downsizing (at 100% a.k.a. 1:1 magnification a.k.a. pixel to pixel) on most monitors.

Actually, the 100% figure relates to viewing, not to the amount of cropping.




  
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Feb 26, 2018 10:36 |  #9

We crop something to 100% because it is often easier than posting a full res image and having the recipient be able to see it at 100% then move to the part of the image in question.

So often 100% viewing and cropping to this level go hand in hand on the web.


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patrick ­ j
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Feb 26, 2018 10:50 |  #10

Left Handed Brisket wrote in post #18572541 (external link)
There is nothing deceptive about a 100 percent crop, at all. If anything, a gaggle of photographers will always default to the nerdiest, most specific definition.

It's deceptive because in the rest of the world, a 100 percent means everything. If I invest in a stock and it loses 100 percent of its value, I have nothing left. If I do a hundred percent crop, I have - whatever.


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Tom ­ Reichner
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Feb 26, 2018 10:59 |  #11

patrick j wrote in post #18572623 (external link)
It's deceptive because in the rest of the world, a 100 percent means everything. If I invest in a stock and it loses 100 percent of its value, I have nothing left. If I do a hundred percent crop, I have - whatever.

Correct.

The term "100 percent" sometimes leads people to believe one thing, when it really doesn't mean that thing ....... therefore it is deceptive.

Anything that leads people to sometimes misunderstand something is, by its very nature, deceptive.


.


"Your" and "you're" are different words with completely different meanings - please use the correct one.
"They're", "their", and "there" are different words with completely different meanings - please use the correct one.
"Fare" and "fair" are different words with completely different meanings - please use the correct one. The proper expression is "moot point", NOT "mute point".

  
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Post edited 3 months ago by Left Handed Brisket. (2 edits in all)
     
Feb 26, 2018 11:16 |  #12

patrick j wrote in post #18572623 (external link)
It's deceptive because in the rest of the world, a 100 percent means everything. If I invest in a stock and it loses 100 percent of its value, I have nothing left. If I do a hundred percent crop, I have - whatever.

lol @ "- whatever"

I understand that it is not intuitive. Agedbriar continued to try to focus in on the reason it is not intuitive ... we are really talking about viewing.

As teamspeed continued, in this type forum, and in this day and age, it is almost always necessary to crop for ease of use.

If we were using 1 MP cameras, and the forum allowed posting 2 MP images, there would be no need to crop. Indeed, back before Al Gore invented the internet no one ever said "100 percent crop" we said "view at 100 percent". Limitations of the internet/forum servers led to the combining of the two terms.


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Post edited 3 months ago by Left Handed Brisket.
     
Feb 26, 2018 11:17 |  #13

One pixel from the original image is represented by one pixel on the screen ... 100 percent of the data is visible.


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Post edited 3 months ago by Wilt. (3 edits in all)
     
Feb 26, 2018 12:14 |  #14

kmilo wrote in post #18572547 (external link)
My original image is 6000x4000 pixels.

6000 times 4000 equals 24,000,000 total pixels

A 50% crop would leave you with 12,000,000 total pixels .... roughly 4250x2867

Even if you resize that 4250x2867 crop to something like 600x400 ... you're still showing a 50% crop of the original.


... or someone needs to teach me this principle as well :)

edit to add: When someone says 100% crop, they mean the displayed 600x400 pixels is exactly equal to the crop of the original ... it's not resized.

It does not help that explanations are throwing in concepts that need not apply. Let us use a mythical example to help you understand:
Starting assumptions for this scenario

  • Let us assume that your monitor of the future is 4800H pixels wide x 2700V pixels (16:9), it is 20.75" tall and 37" wide and is marketed as a 42" diagonal '12k monitor',
    the current state of the art
  • You wish to view a JPG file which is 6480H x 4320V pixels, a 28MPixel image
  • When the JPG image was created by your best friend, he stored it with the JPG 'save for web' option, and so there is no EXIF data embedded within the file
    ...the computer does not know whether the image is to be displayed at 72dpi or 83dpi or 94 dpi or 101 dalmations per inch!


Now the analysis of the scenario...

Your monitor's native resolution displays 130 dots of image per inch (2700 pixels / 20.75" =130ppi)...no resolution characteristics buried within the image file alters that inherent 'ppi' of the monitor, it is inherent to the design characteristics of the monitor. Period. Nothing changes that, except buying a new monitor!
1. We display your image on your 42" monitor at 'full screen'...it has to fit 6480H x 4320V pixels onto a monitor of 4800H pixels x 2700V pixels (16:9). The computer knows the screen resolution, so it computes that it needs to 'throw away' pixels from the image in order to fit the image on the monitor at 'full screen'.
  • Your application shows that the image is at 63% (2700 / 4320)
  • In terms of image display on the monitor, it is effectively fitting 4320 pixel tall image with thee 20.75" monitor height, or 208 ppi -- but your monitor only supports 130 ppi.


2. We display your image on your 42" monitor at 100%...the monitor has 4800H pixels x 2700V pixels, so 'at 100%' the monitor shows a 4800H pixels x 2700V pixels section of the entire image, and 1620V pixels and 1680H pixels are 'off the edges' of monitor.
  • Your application shows that the image is at 100% (2700 /2700)
  • In terms of image display on the monitor, it is effectively fitting 2700 pixels of the 4320V pixel tall image with the 20.75" monitor height, or 130 ppi -- your monitor supports 130 ppi.

3. We display your image on your 42" monitor at 200%...the monitor has 4800H pixels x 2700V pixels, so 'at 200%' the monitor shows a 2400H pixel x 1350V pixel section of the entire image, and 2970V pixels and 4080H pixels are 'off the edges' of monitor.
  • Your application shows that the image is at 200% (2700 /1350)
  • In terms of image display on the monitor, it is effectively fitting 1350V pixels of the 4320V pixel tall image with the 20.75" monitor height, or 65 ppi -- your monitor supports 130 ppi.


Now if your friend had output the JPG with full EXIF data embedded, and the EXIF said the image was '300 dpi', ALL THREE of the above apply with no changes to any of the description because the embedded EXIF data for 'dpi' simply does not matter to your computer display or to the 'fill page' output to your printer!!!

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Feb 26, 2018 12:38 |  #15

Wilt wrote in post #18572694 (external link)
It does not help that explanations are throwing in concepts that need not apply. Let us use a mythical example to help you understand:
Starting assumptions for this scenario
  • Let us assume that your monitor of the future is 4800H pixels wide x 2700V pixels (16:9), it is 20.75" tall and 37" wide and is marketed as a 42" diagonal '12k monitor',
    the current state of the art
  • You wish to view a JPG file which is 6480H x 4320V pixels, a 28MPixel image
  • When the JPG image was created by your best friend, he stored it with the JPG 'save for web' option, and so there is no EXIF data embedded within the file
    ...the computer does not know whether the image is to be displayed at 72dpi or 83dpi or 94 dpi or 101 dalmations per inch!


Now the analysis of the scenario...

Your monitor's native resolution displays 130 dots of image per inch (2700 pixels / 20.75" =130ppi)...no resolution characteristics buried within the image file alters that inherent 'ppi' of the monitor, it is inherent to the design characteristics of the monitor. Period. Nothing changes that, except buying a new monitor!
1. We display your image on your 42" monitor at 'full screen'...it has to fit 6480H x 4320V pixels onto a monitor of 4800H pixels x 2700V pixels (16:9). The computer knows the screen resolution, so it computes that it needs to 'throw away' pixels from the image in order to fit the image on the monitor at 'full screen'.
  • Your application shows that the image is at 63% (2700 / 4320)
  • In terms of image display on the monitor, it is effectively fitting 4320 pixel tall image with thee 20.75" monitor height, or 208 ppi -- but your monitor only supports 130 ppi.


2. We display your image on your 42" monitor at 100%...the monitor has 4800H pixels x 2700V pixels, so 'at 100%' the monitor shows a 4800H pixels x 2700V pixels section of the entire image, and 1620V pixels and 1680H pixels are 'off the edges' of monitor.
  • Your application shows that the image is at 100% (2700 /2700)
  • In terms of image display on the monitor, it is effectively fitting 2700 pixels of the 4320V pixel tall image with the 20.75" monitor height, or 130 ppi -- your monitor supports 130 ppi.

3. We display your image on your 42" monitor at 200%...the monitor has 4800H pixels x 2700V pixels, so 'at 200%' the monitor shows a 2400H pixel x 1350V pixel section of the entire image, and 2970V pixels and 4080H pixels are 'off the edges' of monitor.
  • Your application shows that the image is at 200% (2700 /1350)
  • In terms of image display on the monitor, it is effectively fitting 1350V pixels of the 4320V pixel tall image with the 20.75" monitor height, or 65 ppi -- your monitor supports 130 ppi.


Now if your friend had output the JPG with full EXIF data embedded, and the EXIF said the image was '300 dpi', ALL THREE of the above apply with no changes to any of the description because the embedded EXIF data for 'dpi' simply does not matter to your computer display or to the 'fill page' output to your printer!!!

What?

I think I get what you are trying to say, but man, this is just too much when all that needed to be said I put in bold.


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