DPI settings

[Geoffc]

I spent some time trying to get my head around DPI settings and concluded that it is only relevant to printers. For example, if you have a jpg that is 1000 pixels wide, a screen will display it using 1000 pixels on the wide side. I don't believe DPI is considered.

I have messed around exporting from Lightroom at 72-1000 dpi and the file is the same size.

So, what is the significance of telling people to upload to this site at 1000 pixels and 72 DPI as per this post:

http://nikonites.com/showpost.php?p=177335

I'm happy to be educated on this but I did a lot of reading and playing before coming to this conclusion.

 

[Scott Murray]

I think its to safe guard the images.

Now lets see some pictures from the D5200

Guidelines to adding a photo to your post.

1. Resize photo to 1000px on the long side.
2. Resolution set to 72dpi

These guidelines will be good for viewing on a computer but will not be good for printing. This will help safeguard your copyright.

 

[Don Kuykendall_RIP]

Video won't show more than 72 so for here that is fine but try and print that image and it won't be very good. So stealing it won't get you very far if you plan on reselling it.


Sent from my iPhone using Tapatalk 2

 

[Dave_W]

It has everything to do with the mistaken belief that "dpi" is the same as "ppi". The instructions should instead say "72 ppi". Unfortunately the two sets of initials being so close in form, are getting interchanged and a quick google search will show that mistake is fairly wide spread.

 

[WhiteLight]

Exactly what Dave (and what you said)
DPI is Dots Per Inch - for Paper
PPI is Pixels Per Inch - For on screen display

DPI can vary, but for viewing pics on the screen 72ppi gives the best resolution.
Anything more than is would be wasted as no display needs more than 72ppi.
It is safe as well cos as the ppi increases, the quality of print increases.
You can get a very good print at 200ppi & billboard sized prints at 300ppi.
Uploading images to 72ppi won't help anyone who may steal & try to print, as it will be heavily pixelated

 

[Don Kuykendall_RIP]

Sorry, That was supposed to have been changed but somehow was not. Here is the revised wording,

Guidelines to adding a photo to your post.

1. Resize photo to 1000px on the long side.
2. Resolution set to 72ppi (Pixels Per Inch)

These guidelines will be good for viewing on a computer but will not be good for printing. This will help safeguard your copyright.

You can set it anywhere you want BUT the 72ppi is there to protect you and the 1000px on the long side allows the EXIF to be saved and those who want to see it can. Also the size lets you control more how it looks and allowing the site to resize it smaller

​

 

[Geoffc]

Same point. Do you guys think the number or quality of pixels in a jpg differs because of a PPI setting. I'm not bring funny, but the total pixels = pixels wide X pixels high. What do you think these settings actually do in terms of changing the image.

Try exporting an image from Lightroom 1000 pixels wide at 72ppi then at 200 ppi. I just did and they are identical in size except the exif has different ppi/dpi values.

I've been meaning to do a post on this subject for a while as I think it is often misrepresented. I only started this one as I wondered if I'd misunderstood something and so far I believe my understanding still stands. I would be grateful if someone could post example images of the above settings where it does demonstrate a difference.

 

[Dave_W]

Same point. Do you guys think the number or quality of pixels in a jpg differs because of a PPI setting. I'm not bring funny, but the total pixels = pixels wide X pixels high. What do you think these settings actually do in terms of changing the image.

Try exporting an image from Lightroom 1000 pixels wide at 72ppi then at 200 ppi. I just did and they are identical in size except the exif has different ppi/dpi values.

I've been meaning to do a post on this subject for a while as I think it is often misrepresented. I only started this one as I wondered if I'd misunderstood something and so far I believe my understanding still stands. I would be grateful if someone could post example images of the above settings where it does demonstrate a difference.

The reason they look the same is that your monitor is probably only a 60 ppi screen so that anything above 60 ppi will not so a difference. However, if you tried a 20 ppi image vs. a 70 ppi image you would see a difference. The ppi number being set at 72 ppi allows for an excellent computer screen but will make a horrible print.

 

[Geoffc]

The reason they look the same is that your monitor is probably only a 60 ppi screen so that anything above 60 ppi will not so a difference. However, if you tried a 20 ppi image vs. a 70 ppi image you would see a difference. The ppi number being set at 72 ppi allows for an excellent computer screen but will make a horrible print.

Dave, the file content is identical. I think you're missing my point. There is no more or less detail, the file sizes are identical. Why not try it as I said, or are you suggesting that one of my identically sized files has some nicer pixels in it to enhance my viewing pleasure.

Even on a printer it only tells it how big to print a given image. For example, a 1000 pixel wide image at 100ppi/dpi will be printed 10 inches wide. Change that number to 50ppi/dpi and it will magically grow to 20 inches using the same data. I appreciate these example numbers would not make a nice quality print by my maths ability suits them.

 

[Geoffc]

And just for completeness try a 1 ppi export, it still looks the same and is the same size.

 

[Don Kuykendall_RIP]

And just for completeness try a 1 ppi export, it still looks the same and is the same size.

You are welcome to upload any way you want but we will still recommend the 72ppi to protect others from theft a little better.

 

[Dave_W]

Then you must be doing something terribly wrong because small changes in my ppi result in large changes in my file size. I can't explain how yours isn't.

 

[Geoffc]

Dave, it's interesting that you assume I'm wrong because my facts (See attached images) contradict your understanding. The size of a file in bytes is determined by pixels Wide X Pixels high and that is a fact barring a few meta tags. Explain how you have two files with the same pixel lengths that are different sizes? Perhaps Lightroom doesn't export properly on my PC or basic physics is not behaving as it should!!


I don't want to fall out over this, but I will need to see your files to understand what you're saying. If you're exporting from Photoshop where you specify image size etc etc then you may think you're getting the situation you describe but it will be changing the width and height in pixels as you mess with ppi.

The images below are 1ppi and 200ppi, both are 1000 pixels wide.

 

[Dave_W]

I think I know why you're not seeing any changes. You have to adjust the dimension sizes of your export to accommodate the lowering of ppi. For instance, if you have a 10 in by 10 in dimension, it will have a minimum pixel count in order to fit that dimension. So you can go lower when you're not bumping up against the minimum pixel count to dimensions

Example - 10 ppi, 50 ppi, 100 ppi and 150 ppi

 

[Geoffc]

I think I know why you're not seeing any changes. You have to adjust the dimension sizes of your export to accommodate the lowering of ppi. For instance, if you have a 10 in by 10 in dimension, it will have a minimum pixel count in order to fit that dimension. So you can go lower when you're not bumping up against the minimum pixel count to dimensions

Example - 10 ppi, 50 ppi, 100 ppi and 150 ppi

View attachment 45440
View attachment 45441
View attachment 45442
View attachment 45443

Dave

Thanks for confirming what I've been saying. Your images are different pixel dimensions, mine are not.

 

[Dave_W]

Right, you can't go lower in ppi than your dimensions will allow you to go.

 

[Dave_W]

Try this, set your height and width dimensions at 1 in each and then start playing with the ppi while exporting from LR, be sure to check the "don't resize to fit" option otherwise it will stop your changes.

 

[Geoffc]

Right, you can't go lower in ppi than your dimensions will allow you to go.

Dave, I think we'd better just let this drop now as you have your view and I have mine. I'm not bothered about winning the point as ppi doesn't actually mean anything if you are specifying pixel dimensions so nobody will be injured by this.

Also it's midnight in the UK so I'm going to bed.

 

[Don Kuykendall_RIP]

Dave, it's interesting that you assume I'm wrong because my facts (See attached images) contradict your understanding. The size of a file in bytes is determined by pixels Wide X Pixels high and that is a fact barring a few meta tags. Explain how you have two files with the same pixel lengths that are different sizes? Perhaps Lightroom doesn't export properly on my PC or basic physics is not behaving as it should!!


I don't want to fall out over this, but I will need to see your files to understand what you're saying. If you're exporting from Photoshop where you specify image size etc etc then you may think you're getting the situation you describe but it will be changing the width and height in pixels as you mess with ppi.

The images below are 1ppi and 200ppi, both are 1000 pixels wide.

View attachment 45434View attachment 45435

now download your 1ppi photo and try to print it. I doesn't even show up. Doesn't do a lot of good for someone to steal

 

[Geoffc]

now download your 1ppi photo and try to print it. I doesn't even show up. Doesn't do a lot of good for someone to steal

Don it prints just fine on my PC, I've just tried it to confirm if you have a point and even if your specific software is deciding to take notice of the 1ppi metatag it's only security in the same sense that tying a pink bow across your front door would deter thieves. The only difference between two files if the ppi number in the details tab when you look at its properties. Anyway, as per my previous email, I was only trying to enlighten people to this common misunderstanding and you original post reminded me to do write about it not not start a big debate so I' think I'll leave it at that and anybody interested can try it for themselves.