strange increase in file size

Explorer ,
May 27, 2021 May 27, 2021

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i got some files sized approximatly 800x700px, RGB, 300dpi. the info-window in photoshop shos that the file is about 2.5MB. but on the computer the file size suddenly increase to about 35MB. i tried to save it again, merged all layers, saved as jpg, saved as tiff with zip or lzw, restarted but nothing helped. i also reduced resolution from 300 to 230dpi but gained only few MB. how comes? somebody an idea?

heres what info shows:

Bildschirmfoto 2021-05-27 um 16.55.51.png

 

heres the actual file size

Bildschirmfoto 2021-05-27 um 16.56.01.png

 

i also attach the file

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How to, Import and export, Problem or error

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correct answers 1 Correct Answer

Adobe Community Professional , May 27, 2021 May 27, 2021
The size PS reports isn't all that accurate and if you want to know the actual 'size' the document takes up, the Finder is the way to do so.  Reducing resolution tag from 300 to anything doesn't do anything to alter the 'size'. Reducing the number of pixels (or producing more) of course will. This is just a tag that is used to calculate a possible size (X number of pixels divided by the tag).  Digital images don't have any size other than the space they take up on some storage media. This si...

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Adobe Community Professional ,
May 27, 2021 May 27, 2021

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The size PS reports isn't all that accurate and if you want to know the actual 'size' the document takes up, the Finder is the way to do so. 

 

Reducing resolution tag from 300 to anything doesn't do anything to alter the 'size'. Reducing the number of pixels (or producing more) of course will. This is just a tag that is used to calculate a possible size (X number of pixels divided by the tag). 

 

Digital images don't have any size other than the space they take up on some storage media. This size varies by many attributes even if the document has the same number of pixels: bit depth, layers, file type and possible compression, color space. It's not worth even considering this size due to so many differences. Digital images therefore should be considered in pixel density. And for this discussion I'm going to limit this to one axis (let's say the long axix) and the image is 1000 pixels. 
 The resolution tag places no role in the 1000 pixel document in this respect: 1000 pixels at 100PPI and 1000 pixels at 100PPI are the same: 1000 pixels. In fact you can take a document that has 1000 pixles with a resolution tag of 100PPI, duplicate it and change the resolution to 1000PPI and the two are identical other than for metadata such as this resolution tag. 

Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)

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Explorer ,
May 27, 2021 May 27, 2021

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i am aware of all of this. working with photoshop over 20 years now. i was just a little confused, happens from time to time when you get old 😉 i checked with creating a new file, same size and with 300dpi and it was almost the same size. the actual thing that confused me was - and still is - when i import these pictures (10 of them)  in indesign and make a normal rgb-pdf with 150dpi  it doesnt compress the images. normaly my pdf has about 5 to 10 MB but this one has hundreds of MB. thats why i thought it has to be a problem with the psd in the first place. so i will check the pdf-process then. anyways, thank you dude

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Adobe Community Professional ,
May 27, 2021 May 27, 2021

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Consider saving a TIFF with or without compression: how does PS know before you even do so, which size to report? It can't. Consider opening a layered image and then saving it as a JPEG with any number of quality settings, how can PS report the size? It can't really. The bottom line is; ignore what the 'size' is reported in the palette you show. And again, DPI is meaningless! It's simply a metadat tag. 

Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)

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Explorer ,
May 27, 2021 May 27, 2021

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i dont get why dpi is meaningless. when i have a 100x100px image with 72dpi, then its lighter than the same image with 300dpi. i am not able to change pixeldensity of it, or am i? i thought pixel density has something to do with screens but not actually with the image itself?

 

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Adobe Community Professional ,
May 28, 2021 May 28, 2021

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A 100x100 pixel image tagged as 100 DPI or 1000 DPI is still 100x100 pixels..Neither is “lighter”; they are the same. The metadata is different. 

Yes you can ressmple either. 

 

Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)

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Explorer ,
May 28, 2021 May 28, 2021

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no i mean that a 100x100px image with 72dpi uses less diskspace than the same image with 300dpi

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LEGEND ,
May 28, 2021 May 28, 2021

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"no i mean that a 100x100px image with 72dpi uses less diskspace than the same image with 300dpi" Then it's not the same image. It must be different in some OTHER way than the ppi. Really, the ppi value is just a number in the file.  Perhaps you can post a pair of image files which you believe differ ONLY in ppi, and yet have different sizes, and we may be able to see why this is.

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Explorer ,
May 28, 2021 May 28, 2021

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ha! i just made the test and must confess you are right an i am not. i always meant that the image with higher resolution must be heavier. it seems like magic to me that it isnt. its exactly the same. thanks for teaching an old man a good lesson 🙂

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Adobe Community Professional ,
May 28, 2021 May 28, 2021

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PPI is optional metadata, and is used to calculate printed dimensions.

Pixel dimensions divided with PPI value = Printed dimensions in inches.

So a 2400 x 3000 image at 300 PPI will print at 8 x 10 inches, because 2400/300 = 8 and 3000/300 = 10.

When you export from Photoshop (or use Save for web), the PPI value is stripped out, because it is not required for screen viewing.

If you open an exported file in Photoshop, it gets assigned a PPI value of 72. Photoshop does this to be able to display rulers with physical dimensions, and to display type correctly. The PPI value could be anything, but happens to be 72.

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Explorer ,
May 28, 2021 May 28, 2021

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interesting, i work with photoshop over 25 years and never thought about all of this. i work a lot for print and therefore do most pictures in 300dpi, but always wondered that 72dpi images also looks good. now i know why 🙂

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Adobe Community Professional ,
May 28, 2021 May 28, 2021

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The only case where the file size would change would be with images whose physical changes in CM/IN are fixed, but the PPI changes, in this case the number of pixels will be different.

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Explorer ,
May 28, 2021 May 28, 2021

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as i said above, the case where i discovered strange behaviour in file size is when i render a pdf from indesign where some heavy psd-files are linked in. usually i render a rgb 150dpi pdf for preview. mostly they are quiet light but sometimes, and that was the case this time, it was hundreds of MB in size. thats why i thought it has to do something with the psd in the indesign. so i changed the psd but the pdf kept beeing very big. when i compress the pdf in acrobat, the size dropped to a few kilobytes. its strange because for the most part indesign renders very good preview pdfs. i encounter this behaviour very rarely. maybe sometimes indesign has issues with compression images?

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Adobe Community Professional ,
May 28, 2021 May 28, 2021

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@hemag nova grafik wrote:

interesting, i work with photoshop over 25 years and never thought about all of this. i work a lot for print and therefore do most pictures in 300dpi, but always wondered that 72dpi images also looks good. now i know why 🙂


I wrote my first article for a magazine on Resolution way back in 1998 and I see it's still a topic of confusion today. FWIW, the article is archived here:

http://digitaldog.net/files/Resolution.pdf

Let's start here with some caveats and why I suggest always working in pixels. 

1. Digital images don't have any size other than the space they take up on some storage media. This size varies by many attributes even if the document has the same number of pixels: bit depth, layers, file type and possible compression, color space. It's not worth even considering this size due to so many differences. Digital images therefore should be considered in pixel density. And for this discussion I'm going to limit this to one axis (let's say the long axix) and the image is 1000 pixels. 

2. An analogy is necessary to discuss the resolution tag in digital images. If I'm 6 feet tall and every stride I take is 3 feet, and my friend is 5 feet tall and every stride he takes is 2 feet, when we both walk exactly 1 mile, we walked exactly a mile. That I walked with less strides (resolution) doesn't change that I walked exactly 1 mile (pixels). 

3. The resolution tag places no role in the 1000 pixel document in this respect: 1000 pixels at 100PPI and 1000 pixels at 100PPI are the same: 1000 pixels. In fact you can take a document that has 1000 pixles with a resolution tag of 100PPI, duplicate it and change the resolution to 1000PPI and the two are identical other than for metadata such as this resolution tag. And of course metadata like date/time the document was created and so forth. The two documents are 1000 pixels and the tag has no role and does nothing at this time. Set it for anything you want, as often as you want, it's the same digital image at this point. 

For all intent and purposes, the resolution tag plays no role. The number of pixels does. But wait you say, "I want to output the 1000 pixel image". To a print or on screen. OK, now we have a new size to consider! Let's work with a print. Computers are not too smart, they have no idea what you wish for a print size until you tell it. They do know you have 1000 pixels to use to make the print. What size print do you want? The answer comes about when you divide up the pixels you currently have (more about what you might have later) for this print. Now size can be inches, feet, meters, miles, CM, MM you get the point. Let's stick with inches for this story. You have 1000 pixels and the resolution tag is set to 100PPI. You simply need to understand simple math (division) or have a calculator once you accept you have 1000 pixels. At 100PPI (the tag), a print could (repeat could be), 10 inches. If the tag is 1000PPI, you're going to end up with 1 inch if you allow the computer to provide that division of your pixels. If the resolution tag is 23PPI, the size would be 43.4783 inches (here's where a calculator is useful). It's not if the tag is in MM or CM, or you alter the tag value. But in every case, the data is 1000 pixels. That is the critical number to know about first. The other number can always be changed so software can at this point understand a potential size for output. 

OK, so now Lightroom (or Photoshop or anything else) comes into play. And you ask for that 1000 pixel document to be output to 10 inches at 200PPI. What's a computer and software to do? You don't have 2000 pixels. So the software will interpolate and add more pixels out of thin air so to speak. Or you could reduce the number of pixels with interpolation. This is where Robert got a big flummoxed. He said "I didn't interpolate, LR did". Of course it did! If you ask for output that requires 2000 pixels and you only have 1000 pixels, AND you give the software permission to make more pixels, it will. It will interpolate. It interpolates because you told it to interpolate and make more pixels due to the size relationship with the current tag. 

Now to the deal with sharpening. Until you print the image, it's still 1000 pixels. The PPI tag is moot. But you asked in the print module for a print at a specific size. And guess what, LR sharpens based on what it knows about the number of pixels (current or what you might, repeat might interpolate) and the size you asked for. Output sharpening is output resolution and size specific. So that tag is NOW used. But you still have and have always had a 1000 pixel document san's permission to interpolate adding or removing pixels. 

Work in pixels. Have a calculator nearby if necessary. Pretty much ignore the resolution tag until, if, you need to output that data and you require a specific output size or sharpening in the case of LR. Understand you can allow software to interpolate BASED on the resolution tag. If the tag is 100PPI and you tell LR you want 10 inches, the results are quite different than if the tag is 1000PPI and you tell LR you want 10 inches. You are in control. The software only looks at the tag if and when you tell it to look and use that tag to produce some size with the pixels you have.  

Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)

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Adobe Community Professional ,
May 28, 2021 May 28, 2021

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A 100x100 pixel image tagged as 100 DPI or 1000 DPI is still 100x100 pixels. Same bit depth/color model, NO difference in disk space! The only difference is the metadata. 

Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)

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LEGEND ,
May 28, 2021 May 28, 2021

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Still another way to think about ppi: it gives "preferred size". ppi just tells you a preferred size for the image in inches/mm. The preferred size is the first choice of size when placed in InDesign. The preferred size is the size Photoshop will offer to print.

 

Imagine you have a big pile of photos (printed photos in your hand). You can put a post it note on each one, saying "prefererred size 5 x 7" or "preferred size 10 x 14" or whatever. This is valuable info, but it doesn't make any of the photos better or worse. You can change the preferred size sticker too. Doesn't make the picture better or worse.

 

BUT if your preferred size is too big, and you print that size, and there wasn't enough detail, you will get poor quality. Change the sticker (or don't change the sticker) and have it printed at a lower preferred size, and it might be great.

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Explorer ,
Jun 01, 2021 Jun 01, 2021

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and where does pixel density comes into play?

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LEGEND ,
Jun 01, 2021 Jun 01, 2021

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"Pixel density" is a term sometimes used for the resolution of an electronic device (such as a monitor or scanner). https://en.wikipedia.org/wiki/Pixel_density

It has no effect whatever on file size given the same number of pixels. But of course scanning at a higher resolution makes a bigger file.

It's best not to even think of adding the term to the current discussion!

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Explorer ,
Jun 02, 2021 Jun 02, 2021

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yes i know that. but thedigitaldog mentioned: "Digital images therefore should be considered in pixel density." i guess in this case its meant for describing width and lenght of an image in pixels

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Adobe Community Professional ,
Jun 02, 2021 Jun 02, 2021

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Pixel density: simple. Number of pixels.

1000x3000 pixel density higher than 100x300 pixels. Work in pixels.

Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)

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LEGEND ,
May 27, 2021 May 27, 2021

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There is, in fact, nothing strange about this. PS does not give you the size on disk. 

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Explorer ,
May 27, 2021 May 27, 2021

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read answer above, thank you too

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