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11-30-2016, 06:00 AM   #1
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Picture file size, picture pixel size, resizeing picture, discussion

Ok, in short

WHERE IS SIZE OF EXPORTED FILE MATTER, WHEN YOU have SAME PIXEL RATIO AND ORIGINAL RESOLUTION ?



This thread is not a thread about MP count, not about physical sizes in microM on sensors, not about resizing picture smaller then original resolution.

I suppose it will be open sort of debate, because I will ask here one maybe hardly answered question.


__________________



OK,

Suppose You export your file in Lightroom, lets say "quality 60 % " , and 240 ppi - which is obvious standard for Lightroorm,

and yet again you export same photo in 100 %, and you leave 240 ppi untouched. Picture will be significantly larger, but yet you will not see any visible difference on your monitor. Or you will perhaps, specially if you have some real HD screens to look at... ?

Let's debate and debunked what we need.

----

Same resolution, Picture 4000x6000 = 24 Mpix ( to be clear on this math )

but 100 % Quality vs 60 % Quality does not make any difference on first view. Is the picture quality really intact ??

Size definitively show significant raise - from 3 Mb to even 13 Mb.

But when you examine your pic this is not you will see. You will be ending like -

OK, WHERE THE HELL GOES THOSE MEGABYTES, WHEN I CLEARLY NOT SEE ANY SIGNIFICANT DECREASE or INCREASE IN SCREEN,
EVEN WHEN I SCROLL DOWN MY MOUSE TILL PICTURE ENDS ??


Second,

Let's think about :

What is pixel per inch, and what is pixel resoultion ??
Which size is which size ??

Obviously we're talking about different things, but measurement is not quite clear on this.

Resolution 4000-6000 may came with different measures of ppi . 240, 100, or even higher then 300


I understand physical rule here, but I don't understand all of it obviously. Resoultion is count for pixels, how many of them you deal with.

It's a obvious physic size - Pixel is Pixel, bigger numbers, better zooming in

And this is also called Resolution. in our example 4000 x 6000 = 24 Mpix.

__________

You came on your export in LR, and see 240 ppi.

qUALITY setting as a third - at 60 %.


You set 600 pixel per inch ( I set numueros of my art pics at ridicoules 600 ppi before ), and what's gone changed here ???


sIze of exported pic? Trully yes ! But picture will again be same at resolution of 4000-6000, and where the is the change then ???

Don't quite get it,


AND LET'S DEBUNKED THIS


Last edited by panonski; 11-30-2016 at 06:13 AM.
11-30-2016, 06:28 AM - 1 Like   #2
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That's the magic of data compression at work! The lower the quality setting, the more the compression algorithm throws away tiny details that are not very visible to the human eye. If you subtract the "quality 60%" image from the "quality 100%" image, you'll see what actually changed.
11-30-2016, 06:45 AM   #3
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QuoteOriginally posted by photoptimist Quote
That's the magic of data compression at work! The lower the quality setting, the more the compression algorithm throws away tiny details that are not very visible to the human eye. If you subtract the "quality 60%" image from the "quality 100%" image, you'll see what actually changed.

so this is throwing away... but not very visible.

If it's not visible for my screen, even full cropped, there is no any chance it will be visible in print , no matter how big it is, because 240 ppi, or whatever you'll set it up, will be the same, and printers numbers of printed dots will also be tha very same.

Are there any need to increase your MB file size to even 500 % more MB , when you need much less ??

Is that the real reason why LR is originally set to 60 %, and 240 dpi ?
11-30-2016, 06:49 AM - 1 Like   #4
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That's how compression works... there are interesting YouTube videos on this, one of which was linked here some time ago.
The gist is that the image is divided in square portions and the less-significant information is thrown away.

There is not going to be a significant difference between 60 and 100% compression, that's something to be expected (diminishing returns, I guess...)

11-30-2016, 06:53 AM - 1 Like   #5
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JPEG use a "lossy" compression scheme. The more you compress the more data is lost. Try saving your images at 20% and look at the results.

This whitepaper has some decent examples of the effects of JPEG compression

http://learnmem.cshlp.org/site/misc/tsg_JPEG_instructions.pdf
11-30-2016, 07:32 AM   #6
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visual and audio compression is based on the idea that for its intended use the user cannot detect (or will accept) the loss of information
the idea being that "quality" is relative that good enough is just that... "good enough"

once a file format and its compression rate are chosen everything flows downstream

each compression/decompression cycle introduces some loss of data
enough cycles occur and the accumulated loss can degrade the data to the point that it becomes unacceptable

"lossless" formats preserve data integrity but result in greater bulk
with very high speed data transmission facilities the size of the payload isn't the issue it once was

as always it is a choice
11-30-2016, 07:38 AM - 1 Like   #7
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QuoteOriginally posted by panonski Quote
and yet again you export same photo in 100 %, and you leave 240 ppi untouched. Picture will be significantly larger, but yet you will not see any visible difference on your monitor. Or you will perhaps, specially if you have some real HD screens to look at... ?
Image has 3 things:
a) Dimensions (X and Y, like 6000x4000)
b) image depth (bit depth. This is how much nuance each color has. One shade of red red, or two red, or 16 shades of red, etc. More is better, even if your monitor can only display a few)
c) Image format. DNG, PNG, TIFF, BMP, JPG. Each has its strength and weakness. Jpeg is good because it has a lot of compression. The compression is so good, that you hardly notice the loss in quality! But it is there, if you know what to look for. Hard lines start to get soft, edges become square, sky becomes more monotone, etc. You can probably find examples online. It really depends on image contents

(( d) PPI is another issue, but it is only important for print. On digital monitor the PPI is ignored.
e) Color space is also important, but very advanced. For now, just make sure you use the same color space in-camera, in software, and in final export. Usually you want sRGB ))


If you upload it, most websites will re-size and re-compress the image! This can make quality look much worse. You should look at the website standards and compress the image in such way, that the website does not ruin it. For example, facebook and even some photo websites are known to be very bad in this

Last edited by Na Horuk; 11-30-2016 at 07:46 AM.
11-30-2016, 09:37 AM - 1 Like   #8
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Regarding jpeg compression, it essentially tries to throw away data that human eyes aren't great at detecting. Throw away too much and you start getting artifacts that will be visible on even a small screen. You may find a pretty low setting (e.g. 60 in lightroom) may be hard to distinguish from the original image. It depends on the image content, and how you're actually viewing the image, how picky you are, etc.

This site has some great comparisons: Jeffrey Friedl's Blog An Analysis of Lightroom JPEG Export Quality Settings


Regarding the ppi setting on the lightroom export, there are two cases:

1) You are setting the Width and Height boxes in terms of pixels. In this case, the Resolution box (either pixels per inch or pixel per cm) essentially does nothing. It's just a note in the exif data but won't change the image that you output when viewed on your screen (but for most applications these days, this exif note won't matter, see All About Digital Photos - The Myth of DPI for more info).

2) You are setting the Width and Height boxes in terms of inches or cm. In this case, the Resolution box (either pixels per inch or pixel per cm) will then be used to calculate the pixel dimensions of your output. eg. width of 10 inches and height of 15 inches at 300 pixels per inch gives a file 3000 pixels across and 4500 pixels high. The pixels per inch (or cm) will also be a note in the exif data.

Pixels per inch gives a way to relate the pixel dimensions to an actual physical output size, you can use either case above to make print ready files. For example, if you want to make an 8"x12" print and the printer specifies a 300dpi image, you can use case 1) above and just set the Width to 2400 pixels and the Height to 3600 pixels, or you can use case 2) above and set the Width to 8", Height to 12" and the Resolution to 300 pixels per inch. Either approach gives you the same output file.

11-30-2016, 11:45 AM - 1 Like   #9
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take a very plain image - a flat white wall, or a simple text sign - something with sharp borders between large blocks of color. Compress that with JPG and you'll definitely see the compression happen. JPG is terrible at flat fields, it leaves weird square blocks of slightly different color floating around. That's why in the good old days of web, you'd use GIF for anything like that, and JPG for anything with lots of detail and smooth transitions between colors, JPG was cool with those.

You can see a bunch of info and examples of compression artifacts from jpg here: image quality - What are jpeg artifacts and what can be done about them? - Photography Stack Exchange


As for PPI, I don't think you understand what that is. It has nothing at all in any way shape or form to do with the image contents. When you say 300 PPI or 600 PPI you're saying "I want the default printed size for this to have 300/600 pixels per inch" - so if it's a 3000x6000 pixel image, you're saying you want it, by default, to print it at 10x20 inches (or 5x10 inches at 600). When you actually try to print the image, you can change that setting without modifying the image data at all.

---------- Post added 11-30-16 at 01:48 PM ----------

Here's a sample of JPG compression at 50% on a flat color block
12-01-2016, 03:11 AM   #10
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OK, things are clearer now.

- PPI has nothing to do with image size and quality, it's only order for printer ? So, if I export same pic as 10 ppi, vs 300 ppi, it will not be shown on screen, only on print pic ?

- Resolution is clear

- Quality is compressing - and here I have doubts - what is enough, what is not enough - where is the border ?

LR have by default 60 % - is it enough for most cases ?

I know you can always find some artifacts, but is it visible on 60 %, or perhaps it's visible only at low 20 % ?

In my eyes 60 % vs 100 % have no difference - and I'm scrolling pic as much as I can. In print size this will be even less visible - if it is visible at all - even on screen.


SO; is it 60 % in LR just enough ?

Certainly, I would love to save my pic at MAX QUALITY, but I'm just curios on that, because sometimes I must delivered to clients - very large number of files, and if you have more then 100 of them, it's very convinient to be smaller, rather then larger.

Method I'm using right now is saving my pics in LR at 300 ppi, and 100 % quality - and after that, choosen ones for delivering to client - just resize with VSO Image Resizer ( higly recomended free and very powerfull resize tool )

and I choose ORIGINAL RESOLUTION - QUALITY 70 % .

It downsize my image from 14 MB, to 3 MB, and as I said - pic look preety the same as original. ( or same in my eyes )

---

One more tip, now as I mention VSO here. iT HAS also a name LIGHT IMAGE RESIZER. Don't know the difference, I have on my laptop Light Image, and on Desk VSO, but its the same program

I use this tool more then 5 years, and I tried some of "best" resizers on internet . Non of them was nearly so good in exporting quality in small size like VSO. And some of this of the best ones was just disaster in ruining colors, or overall quality. But not with VSO

I have my web, and for my web, I must be at a lower file size. VSO have it's own default profiles which you can change in a manner you want to.
--
If you want decrease or increase VSO output quality, file size, picture ratio, algorhytm for compression, even add your watermark,
you will be asked to save changes as your new profile, and from now on, you can just open it, go to your profile click it, and export your pic.

You want add some more pics to this when you finished your first one - just drag and drop all of them into VSO box, and click it again.
File name is the same ? No problem also. VSO will rename it, and you will be ask before.

Very convinient - and high quality tool ! You can have shortcut on right click on image, it can be on desktop, or in system desktop tray.!


After numerous trying to keep smaller picture, and enough quality on it, ( JUST FOR WEB USE! ) I came to perferct measure ( at least for me ) .

IT IS : 1600 x 1200 ( it satisfied most of screen sizes ) ; Quality set : 60 % ; Exif data : NONE ( it will spare more space, and no one would know anything about your picture details )

Picture will be small like 200 KB cca, even less, and quality of file would surprise you !


_____________

by the way - Thank you all on this thread !

Last edited by panonski; 12-01-2016 at 03:40 AM.
12-01-2016, 06:55 AM   #11
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QuoteOriginally posted by panonski Quote
- PPI has nothing to do with image size and quality, it's only order for printer ? So, if I export same pic as 10 ppi, vs 300 ppi, it will not be shown on screen, only on print pic ?
Yes, but to be clear the printer won't care what your ppi setting was when you exported from Lightroom. What matters is the files dimensions in pixels, and the print size you tell your printer to produce.

For example, export a file from LR four times with these four settings:
  • 2400x3600 pixels, ppi 1
  • 2400x3600 pixels, ppi 300
  • 8"x12", ppi 300
  • 16"x24", ppi 150

Then send them to the printer with instructions to print at 8x12", the results will all be the same.

QuoteOriginally posted by panonski Quote
- Quality is compressing - and here I have doubts - what is enough, what is not enough - where is the border ?

LR have by default 60 % - is it enough for most cases ?
It really depends. As you've noticed, 60 is pretty darn good, and sufficient web use in many cases, but it's really a balancing act between quality and slowing down loading times. For a "one setting fits all", I'd probably knock it up a bit, but there's no one right answer here.

For sending prints to a lab, I'd definitely go higher quality as these files are being transmitted once and I can wait a few extra minutes.

For sending files to other people, it really depends on what their end use will be and also how you're going to be delivering the files to them.

The link I posted above to Jeffrey Friedl's page is worth checking out if you haven't already. It has terrific examples of jpeg quality vs file size for several different images, and is specifically talking about some of Lightrooms output quirks.


About VSO, I've never used it but most of the things you've mentioned are also available in Lightroom? If possible, you usually want to avoid exporting jpegs then re-compressing them with another program. Each time you do this, you will lose some quality as the jpeg compression is lossy. There's a good chance this extra loss from running through VSO won't cause a noticeable difference so if you find it that convenient, keep using it, but it's something to be aware of.

You might look into the LR/Mogrify plugin for Lightroom, it gives you a ton of extra options for exporting.
12-01-2016, 08:38 AM   #12
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Thank you for your LR resize plugin tip.

I found VSO is very similar quality like LR, same percentage, same results. But it's more convinient. Instead of opening LR which use much more time, I have this little tool every time I want use some of my pics resized. Usually all of them are saved only in highest quality

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