Facebook Compression

[MattGrey]

Send me a 72ppi image in an e-mail, let me play with it!

Edited June 24, 2014 by MattGrey

[Black Pearl]

Right then:

 

This is a full sized TIFF file I resized specifically to share on the web - here to be precise.

 

 

I changed it so the long edge was 1000 pixels long as that gives a decent viewing experience for most people with modern HD monitors. 

 

1000x776 @ 300ppi - 1.91mb

 

1000x667 @ 72ppi - 1.91mb

 

Out of interest and for those terrified of images being stolen who think 1000 pixel is too small this is the same file but displayed in inches - at 6x4 you get 166ppi which is perfectly acceptable for inkjet printing. Thats not resized to 166ppi that is just changing the way Photoshop displays the file information. Remember ALL of these files are 1000 pixels along the long edge as ALL of these files are EXACTLY the same.

 

6x4' @ 166ppi - 1.91mb

 

By all means download it and have a play but I assure you that changing the ppi will not change the quality in any way UNLESS you interpolate the file to add or subtract pixels but that is an entirely different argument and one where even more people don't know what they are talking about.

 

Ps. Yes if I tried to print the file without having a single jot of common sense the 72ppi one would try to output itself to the printer at 13.889x9.264 inches while the 300ppi one would fire itself at the printer at 3.333x2.223 inches but I'm guessing were not all that stupid.

[ChrisLumix]

Right then:

 

This is a full sized TIFF file I resized specifically to share on the web - here to be precise.

 

ppi myth.jpg

 

I changed it so the long edge was 1000 pixels long as that gives a decent viewing experience for most people with modern HD monitors. 

 

1000x776 @ 300ppi - 1.91mb

300ppi.jpg

 

1000x667 @ 72ppi - 1.91mb

72ppi.jpg

 

Out of interest and for those terrified of images being stolen who think 1000 pixel is too small this is the same file but displayed in inches - at 6x4 you get 166ppi which is perfectly acceptable for inkjet printing. Thats not resized to 166ppi that is just changing the way Photoshop displays the file information. Remember ALL of these files are 1000 pixels along the long edge as ALL of these files are EXACTLY the same.

 

6x4' @ 166ppi - 1.91mb

6x4.jpg

 

By all means download it and have a play but I assure you that changing the ppi will not change the quality in any way UNLESS you interpolate the file to add or subtract pixels but that is an entirely different argument and one where even more people don't know what they are talking about.

 

Ps. Yes if I tried to print the file without having a single jot of common sense the 72ppi one would try to output itself to the printer at 13.889x9.264 inches while the 300ppi one would fire itself at the printer at 3.333x2.223 inches but I'm guessing were not all that stupid.

 

Thanks for the mini tutorial BP. I've assumed all the way through this topic that you didn't think I was that stupid to think that changing the ppi ON ITS OWN makes any difference. Of course it doesn't, while the file stays on the computer. It's like changing the file type of an .aif music file to be .mp3 - the computer will grumble at you but eventually let you do it. However, the file remains the some size, and is still an .aif despite the change of label to .mp3. I've taken that as read without specifically saying it, as I assumed - at the risk of repeating myself - that you didn't think I was that stupid.

 

On another forum, where members regularly complain that their pictures are too big to upload, I give them 3 steps to follow in the image editor of their choice :

1. reduce the absolute image size, in other words make the image no larger than 1000 pixels wide as that's quite large enough for a computer monitor

2. change the ppi from whatever it is to 72 or 90 ppi which is high enough (I don't specifically say "this will have an effect because the image will be resampled" as they will either know this, or it will go over their heads without further lengthy explanation)

3. save the resulting image as a JPEG at medium compression

That gets their image down to a size that should easily be within the forum's posting limit.

 

I realise this discussion was originally about Facebook, but the same principle applies. I would advise anyone posting to FB to first REDUCE the size of their image for Web posting, and (as it's going to be resampled) the ppi for computer viewing, i.e. 72 or 90 ppi, and finally to compress the jpeg from high quality down to medium quality, as no-one else on Facebook is going to either notice or care ... unless they are all members of a photographic club, in which case FB is NOT the best place to post their pictures, due to the byzantine and constantly changing nature of FB's privacy settings, which make posting one's intellectual property a highly risky undertaking.

[Black Pearl]

You could make that two steps.

1. Resample the image to 1000 pixels.

2. Save as a medium quality jpg.

It doesn't need your step 2 as the ppi makes no difference. By all means continue to do it to your images and by all means continue to promote the myth to others but it doesn't stop it being pointless and it won't stop me trying to educate people.

[Guywiththebeard]

I'm now totally lost - what is the best to post to a forum?

[Black Pearl]

Easy

1. Resize to 1000 pixels

2. Save as a medium quality jpg.

Simples :-)

[ChrisLumix]

You could make that two steps.

1. Resample the image to 1000 pixels.

2. Save as a medium quality jpg.

It doesn't need your step 2 as the ppi makes no difference. By all means continue to do it to your images and by all means continue to promote the myth to others but it doesn't stop it being pointless and it won't stop me trying to educate people.

 

But it's not pointless! You said yourself that if the image is 'resampled / reinterpolated' it takes effect. 

[Black Pearl]

It is pointless if you've already set it to 1000 pixels. If you set a print size and a ppi and blindly hoped the pixel size would be what you wanted it would matter but that's a darn odd way and frankly unreliable way to resize an image.

[Guywiththebeard]

I'm now totally lost - what is the best to post to a forum?

Sorry - didn't realise there was a page 2 - not lost no more

[ChrisLumix]

I'm a bit fed up banging my head against a brick wall, so I'm just gonna post this and then leave this topic altogether.

 

 

http://99designs.com/designer-blog/2013/02/26/ppi-vs-dpi-whats-the-difference/

 

Especially this part:

 

"So next time someone tells you to upload images to a website at 72ppi because that is “web resolution,” you can tell them that they have simply added a ridiculous extra step. Unless they are concerned with visitors taking the images from the website and then printing them, the PPI doesn’t matter. A 72ppi image and a 3,000ppi image will appear exactly the same on screen."

 

The highlighted part is what I've been trying to say all along, especially as this topic is to do with Facebook, and that clause is - or should be - our main concern when it comes to that particular site if we want to protect our intellectual property.

Edited June 25, 2014 by ChrisLumix

[Black Pearl]

Well I shall never get tire of proving the myth entirely wrong that changing the ppi of an image without changing its pixel is utterly pointless if you are viewing it onscreen --  AND --  if you're hoping it will have any affect on the prints.

 

Even though I have proved it pointless with screen grabs of the actual files I still see people saying you need to set pixel dimensions and ppi....you don't.

 

I want to give up as I do feel like I'm banging my head off a brick wall but I shan't - it is inaccurate advice.

 

Have a look at my examples above - the two files are both 1000x667 pixels so please (honestly I'm dying to know) tell me what is difference is.

[colinb]

Easy

1. Resize to 1000 pixels

2. Save as a medium quality jpg.

Simples :-)

 

 

annoyingly I have just followed the above instruction and ended up with a file size of 402kb

 

I have also just re-sized the same original file down to 72dpi at 1000 pixels wide and ended up with a file size of 402kb  both saved for web at 80%

 

BP may sound like a smart arse but he is correct      

[FUJI]

Numbers! Numbers!.............I have Discalculia, s they mean not a thing to me.....stop it!     

 

FUJI

[Black Pearl]