DPI not correct after export

[JimmyJack]

… and one more annotation:

• Place an image of type (1.) in a layout application and save it. Examine the file size of this document.

• Place an image of type (2.) in a layout application and save it. Examine the file size of this document.

• You see the difference?

 

Attached two tiffs: (1.) 2480 px x 3508 px, 300 dpi and (2.) 2480 px x 3508 px, 72 dpi

 

 ​Both are exactly the same file size  :).

 

Everything else is an appropriate screen approximation of print size so we don't lose our minds going from digital to physical. It's what the programs are made to do after all  ;).

test size 1 300.tiff

test size 1 72.tiff

[R C-R]

Attached two tiffs: (1.) 2480 px x 3508 px, 300 dpi and (2.) 2480 px x 3508 px, 72 dpi

 

 ​Both are exactly the same file size  :).

It may be worth pointing out (again) that the tiff format does not actually store a dpi setting, just sets of three tag values that indirectly define the size of what can be each of any number of individual images stored in a tiff file (one set per image), & that the formal ISO specifications for "TIFF Readers" (basically, anything that can open or process a tiff file) specifically state that they may use or ignore these tags for print, display, or any other purpose.

 

There is much more to it than that. For example, image pixel data can be stored in several different ways (like as strips or tiles) & each of these can optionally be compressed individually with several different types of compression. Private tags may be included to store proprietary info that TIFF Readers may ignore. Tiff supports five different types images, plus vector-based clipping paths.

[mac_heibu]

I give up! Obviously no DTP-experts here!

Perhaps tomorrow 2 screenshots of the issue Affinity is causing in this context. But – no worries – "screen designers" will not notice the problems, and print designers don't usa Affinity for now.

[mac_heibu]

Attached two tiffs: (1.) 2480 px x 3508 px, 300 dpi and (2.) 2480 px x 3508 px, 72 dpi

 

 ​Both are exactly the same file size  :).

 

Everything else is an appropriate screen approximation of print size so we don't lose our minds going from digital to physical. It's what the programs are made to do after all  ;).

You didn't read exactly and didn't really get the problem! Of course the file size of the images are identical! But, as I wrote,  you shouldn't compare the file size of the images, but the file size of the layout document (Quark, InDesign), where the images are placed! And please, no assumptions! Just try it, if you have acces to one of these layout applications!

[anon1]

yeah mac_heibu it´s because the layout program places the image based on the size and then recalculates the output with the DPI/ PPI of the document (although you can change that)

So if you set a lower DPI/ PPI for the picture and then place it in the program and then export it it will take more space on the canvas and thus have a bigger file size than the picture that was brought in at a higher DPI/ PPI.

 

There is also the fact that it is very easy to check if the resolution is enough for planned print size when you have correctly working image size dialog.

 

yeah

[mac_heibu]

• If I place a 2480 px x 3508 px image with 300 dpi resolution (300 dpi, because I want and need it for print), in InDesign for example, it is very simple, clear and streamlined to work with: The image fits precisely onto an A4 page and I can control  the picture’s output size already in my image processing software. Placing these images in InDesign is nothing but a click.

• If I place a 2480 px x 3508 px image with  72 dpi resolutions, it is absolutely ridiculous and painful to work with: It is placed way to large in a way to small resolution. You have to zoom out and scale down every single image to attain its desired size.

Just imagine, what that means, if you have to create a large format photo book with, lets say 350 pages (as I did some weeks ago). Never – and I say never – I would do this, if my image processing software doesn’t allow to determine the output size of my images in advance.

And more: Though of course linking to the assets, layout applications keep previews of the placed images within its document file. Lower resolution preview images have larger dimensions compared to higher resolution preview images. Therefore the file size in this case will be much bigger. Using CMYK images, the file size of the InDesign document, which you see in the attached screenshot is 1/4 bigger, when you use 72 dpi images instead of 300 dpi images. You may imagine, that this makes a heavy difference regarding my above example of a photo book, containing 350 pages and tons of high format images.

As attachment you find an commented and, as I hope, selfexplaining screenshot to illustrate all this.

 

 

[R C-R]

And more: Though of course linking to the assets, layout applications keep previews of the placed images within its document file. Lower resolution preview images have larger dimensions compared to higher resolution preview images. Therefore the file size in this case will be much bigger.

An image of any given pixel size will require exactly the same number of bytes to store it regardless of the dpi setting, which just specifies a default value for the spacing of the dots when pixels are converted to the equivalent of dots during printing.

 

Lower resolution previews contain fewer pixels (they are down-sampled in much the same way as resizing is done in Affinity) & therefore require less file space for storage, not more.

[mac_heibu]

Don’t talk, just try! I’m really fed up arguing against users, who – excuse me – don’t really know, what they are talking about. I think you never have been confronted with these kind of "problems", but nevertheless you know exactly, what goes on!

Extra for you:

• I took an image (3556 px x 5184 px, CMYK) and saved it (a) with a resolution of 300 dpi and a ( B) with a resolution of 72 dpi – of course without any(!) downsampling or upsampling the image. As expected, both images have the same file size of 71,7 MB.

• I place the first image in a newly created, blank InDesign document and saved it.

• I place the second image in a newly created, blank InDesign document and saved it too.

• You can compare the file sizes of both documents by having a look at the attached screenshot.

Believe me, if you’d use QuarkXPress this stunning difference of round about 1/3 of the file size will be even bigger! The reason is the way, layout application manage assets internally. But this really would lead to far in this thread.

 

Again: Is it really necessary to argue in this thread without even trying to investigate the problem?

[geirrosset]

Just to back up mac_heibu here. I'm a publisher (print) and it seems that there are a lot of answers here from folks who do not work in publishing. Nevermind the technical aspects of file types or pixels vs dpi vs quality.  There is no issue for screen based designers, but that doesn't mean that Affinity Photo can't be fixed to work equally well for print designers. Attached is a screen dump showing file info for two blank Quark XPress 2016 files with the same photo inserted at 300 dpi and 72 dpi. That's half a MB difference for a document containing one photo. The photo files are the same size (725Kb), the layout files are not. Now scale that layout file up to include a couple hundred photos, lots of text, fonts and graphics and you should begin to see what the problem is about.

 

Just let us open a (72 dpi) jpg in AP, change the dpi (to 300), leaving the pixel dimensions the same, check that the print size in cm/inches is sufficient for your layout and then save and close it (you can do this now, but nothing is written to the file). Shouldn't be than hard to fix. As a publisher I see graphic files at anywhere from 1 dpi (yes that's 1 dpi) to 4000 or 6000 dpi (all because most authors have no idea what they are doing when it comes to images or scanning).

 

FYI: Increasing the dpi further will further decrease the size of the layout document, but will force you to scale the image up in your DTP software so there is no point. So this is really a matter of how DTP software works and how badly Affinity want's DTP customers to switch to their software. I doubt Affinity can change the way Adobe or Quark handles images in their documents.

[Jupiter]

If the DPI function is working correctly, then if we have a file size of 1000x500 at 72 dpi, then scaling to 300 dpi should result in a file 300/72 times larger (or 4.16 times, 4166x2088).

 

If it is not doing this, it is failing.

 

This is a problem as I print photos I have taken, and necessarily adjust the DPI for the print process and output size. I'm just a private user looking to buy this product as it looks very promising, but this is a glaring problem.

[anon1]

The issue is that you're not gaining much information but mainly just blowing up the file size.

If I upscale 1 pixel to 4 pixel for example I don't gain any information.

 

You only get a bit of an improvement depending on the reeamoling algorithm but going from 72 to 300dpi is pretty heavy.

 

You should either take higher Megapixel photos so that these match your print size at 300dpi or higher or you should print your photos smaller.

[Jupiter]

It was for example only. I wouldn't try that kind of scaling! :)

[R C-R]

If the DPI function is working correctly, then if we have a file size of 1000x500 at 72 dpi, then scaling to 300 dpi should result in a file 300/72 times larger (or 4.16 times, 4166x2088).

If by scaling you mean resampling, & you are talking about a raster (bitmap) image then yes, the pixel dimensions will change proportional to the change in dpi.

 

However, the change in file size depends on several factors, including the internal format of the image data (like if it is compressed & if so, how), what if any metadata or proprietary features (like history or snapshots) are stored in the file, & if you are saving the file in the app's native file format or exporting it to another supported format (like tiff, jpeg, png, or pdf).

[accidemic13]

First, apologies for having just started a new thread on this topic: in my "exasperation" (which I expressed in the title of my thread), I missed this current thread, albeit even after many searches of the forums.

 

But this topic is doing nothing to assuage that exasperation, despite the efforts of certain of those engaged here who seem intent upon ignoring or simply unwilling to recognize the simple complaint at the heart of this thread (one voiced by many of the above posters, especially the designers) going back to the OP: the "Resize Document" dialogue in Afinity Photo does not work like the "Image Resize" dialogue in Photoshop, and it's unnecessarily confusing for all of us who want to switch from PS to Affinity Photo. Personally, I understand DPI, resampling, resolution, etc., and I frankly don't care if "dpi" is a legacy term that no longer means what it used to and that I may even be confusing for "ppi" or anything else. The fact of the matter is, as a photographer whose editing and printing his own work, I want to see all the parameters in the Resize Document dialgoue; when I uncheck "resample", I want to see the way the output dimensions of my image, in inches, will change when I reduce the "dpi" from 4800 to 300, so that I know at exactly what size I'll be able to print; and when I effect these changes in the "Resize Document" dialogue in Affinity Photo and then save these changes, I want to be able to reopen the document at the new dpi I just set (with its corresponding new output dimensions)... whether or not it's "real dpi" or just a place-holder that we've all become accustomed to after decades of Photoshop. What's the point of even having a "Resampling" box to uncheck and a corresponding DPI setting to alter if we can't see how the change is being reflected in output dimensions, and if whatever changes we make there will be erased or ignored upon saving anyway?

 

Honestly, this just seems like something so basic, that any non-destructive digital photo editing software should institute off the bat. It's something Affinity Photo should fix for "the rest of us." The number-crunchers out there are welcome to use their calculators to compute their output dimensions for print everytime they open a document... but I'd prefer the software to make this calculation for me and save me the hassle.