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RESOLUTION BUG

Forum|Forum|3 years ago
May 11, 2022
20 replies
3029 views

Files with different resolutions, 300 and 72ppi are saved with the same size.

If I create 2 files of 1920x1080, 1 with 300ppi and the other with 72ppi.

I open any image, from an image bank, with 300ppi and I drag this image into both files, the image is displayed in both as if it were with 300ppi.

It's as if the resolution option on creating and saving files is not working.

I already formatted my machine and reinstalled everything, the problem remains.

Windows

This topic has been closed for replies.

Correct answer TheDigitalDog

Yes, they are the same size because that is just a metadata tag that has nothing to do with size. The image 1920x1080 pixels, that's what determines the size, color space, and bit depth being equal. IOW, 1920x1080 at 72 and 300 and 3000 or any value is identical. Work in pixels.

This is old, but nothing has changed since it was written and you need a primer on resolution:

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

ZequimAuthor

Known Participant

Friends I come to apologize, I was really wrong.

I don't know why in my mind I was treating resolution as PIXELS and not POINTS.

I think it's the time away from any graphic material that bugged my mind.

For the record to fall I needed to create 2 1x1px files with different resolutions to understand that I was talking about POINTS not PIXELS.

Sorry for the inconvenience.

Thank you for the effort to open my mind.

D Fosse

Community Expert

I think the main reason for all this confusion is that the term "resolution" can have two subtly different meanings. It can either mean total number of sampling points (pixels) - or it can mean sampling points per unit of measure. Often the two are the same, but for an image they're not.

The confusion might be reduced considerably if we termed the first "resolution" and the second "density". Pixels per inch is unambiguously density, not resolution.

Used in this sense, resolution doesn't imply scale or size. The size is simply "all of it". Density, on the other hand, requires that you define a scale. It makes no sense without it.

So, to take an image as an example, it may have a resolution of, say, 1920 x 1080 pixels. It can be reproduced at any pixel density you want, 72, 300, 466.667, etc. The resolution is a property of the file. The density is set arbitrarily per reproduction instance.

D Fosse

Community Expert

I kind of agree Dag, however many applications, including Photoshop, use the term resolution for ppi. so it would require an awful lot of change through the industry and to get traction on that. It's hard enough getting ppi used instead of dpi

Dave

Yes, and the way this is commonly used, by accepted convention, "resolution" is in fact the strictly correct term for ppi. So an actual semantic change is unrealistic, I understand that.

But by way of explaining the underlying concepts, "density" might be a useful word. Because there is a real difference in these two meanings, we just have no standardized way of expressing it.

ZequimAuthor

Known Participant

Please friends, understand, you are talking to someone who has been working with Photoshop for 15 years for COUNTLESS PURPOSES.

Printed Graphics

Digital

or any other end product

davescm

Community Expert

"..understand, you are talking to someone who has been working with Photoshop for 15 years...."

As have we, in my case 19 years.

You have not clarified what you mean by file weight (it is not a technical computer expression) but I do sometimes see it used to mean file size on disk. That file size on disk depends on the following:

a. Bit depth (each pixel can be represented by 8, 16 or 32 bits per channel. So each pixel in each channel uses 1 byte, 2. bytes or 4 bytes)

b. Image mode - CMYK has four channels RGB three

c. Layers (including smart objects)

d. Additional channels such as alpha channels

d. Pixel dimensions i.e. x pixels wide by y pixels high - this has a huge impact

e. Compression which reduces file size on disk. The amount of compression depends on both quality settings, for those alogorithms that offer variable compression such as jpeg, and image content - some content compresses better than others

f. The amount of non image metadata

Image resolution (ppi) has no impact whatsoever on the image file size on disk. The value 72ppi and the value 300ppi does not increase the file size on disk, it is just a number stored alongside the image data.

Dave

ZequimAuthor

Known Participant

Friends, don't get me wrong, I understand that you have even more experience than mine.

I'm just making it clear that you're not talking to a beginner.

ZequimAuthor

Known Participant

All my life I managed to take the same image and save it with different resolutions and file weights.

Keeping the same pixel size.

In other words, the same image of 1000X1000px

But with different resolutions and file weights.

But overnight I went crazy and stopped understanding how images and their properties behave.

davescm

Community Expert

"The problem is not the scale or the aspect ratio, the problem is the resolution, quality and weight of the file,"

The quality depends on the number of pixels in the image.

The weight of the file - presumably you mean the file size saved on disk. That is a function of the number of pixels and any compression set. ppi does not affect it, it is just a number stored in the metadata.

Resolution - that is pixels per inch (ppi) and only comes into play when converting to a physical print. On screen it is irrelevant and displayed resolution is purely a function of the monitor pixel pitch.

Dave

TheDigitalDog

Inspiring

Within PS no. But we've been over this.

https://www.youtube.com/watch?app=desktop&v=qYe8cGy9TeI

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

ZequimAuthor

Known Participant

Yes, because you're not getting my point.

ZequimAuthor

Known Participant

But that's exactly what I'm saying.

It is obvious that 1000x1000px will always be 1000X1000px regardless of resolution.

The problem is not the scale or the aspect ratio, the problem is the resolution, quality and weight of the file, friends.

TheDigitalDog

Inspiring

Good luck Dave; I'm getting nowhere.

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

davescm

Community Expert

Zequim

You are missing the point.

A 10 inch wide document at 72ppi will be 720 pixels wide

A 10 inch wide document at 300ppi will be 3000 pixels wide

BUT

A 3000 pixel wide document at 72 ppi will still be 3000 pixels wide

A 3000 pixel wide document at 300ppi will still be 3000 pixels wide

ppi is just metadata stored alongside the image data and is used by the print driver to calculate the physical size, in inches, when printing and the ruler size when shown on screen with a inch or cm ruler. Aside from calculating that ruler, an image on screen ignores ppi data altogether. All that matters is pixels. 100% zoom means 1 image pixel mapped onto 1 screen pixel. ppi is irrelevant to that mapping.

Dave

TheDigitalDog

Inspiring

Got nothing to do with proportion friend.

The pixels are the same size in the example I proided. The zoom ratio doesn't change that fact. Add more pixels and that changes the size. 100 x 100 pixels at 72 PPI and 100 x 100 pixels at 1000 PPI are exactly the same size.

Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"

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