Improve the export function to allow changing DPIs (resolution)

[eadauto]

Hi,

I use to export my images on LightRoom or Luminar and I have the option to change the DPIs when exporting. Example if I'm posting on FB I use jpg 72 DPIs, 90% quality and 2048 on the longest side but when I want to deliver full resolution I just keep 300 DPIs and no resize .

Here I can change the size & quality but not the DPIs so I need to go to document and change it to 72 (when my original picture was 300 dpi), export and then undo on history as I don't want to create one document per DPIs resolution.

Can you add the possibility to change DPIs directly on the export regardless the document size?

[Andy05]

DPI don't matter if you define your image's size in pixels. A digitally stored image has no inherent physical dimensions like inches. 1000x1000 pixels is 1000x1000 pixels - no matter what DPI setting you want to set. DPI is for print and Facebook doesn't care about that setting for displaying images. Unfortunately, even "professional" programs often use this term wrongly.

Displays have pixels, not dots per Inch. So 1000 pixels are shown 1000 pixels wide (at 100% scale) regardless if you "set the DPI" to 300 or 72 (or whatever other value). What matters is a device's PPI (Pixels per Inch), which will have an effect of how big the image is actually shown on your device. 

[paristo]

• Resolution = how many pixels in digital image width and height. Example 1920 x 1080, 800 x 600 or 3000 x 2000.
• Definition = how many pixels per physical area by viewing distance. Example 1280 x 720 or 1920 x 1080 viewed from 43", 50" or 55" television at 1,5 m, 2,2 or 3,1 meters. (eye limited.)
• Pixel density = In physical material dimensions that how many pixels are to be scanned or printed per area. Example 72 PPI, 180 PPI or 300 PPI. (pixels per inch.)
• Printing definition = how many ink dots (picoliters is another topic) used per area to print a single pixel. Example 300 ink dots used to print 72 pixels on inch, so 300 DPI (Dots Per Inch). (another discussion for printing)
• Scanning definition = how many pixels scanner reads per physical area from physical medium. Example 150 PPI, 300 PPI or 600 PPI.

 

There is a big difference what people means with "resolution" as most do not know that digital image has no dimensions, only a resolution. And it is up to printer and scanner capabilities and settings to be used in conjuction with the physical measurements that creates a dilemma for many. And 72, 270, 300, 600 pixels/dots per inch is nothing more than a multiplier to be used with actual pixel resolution to translate physical dimensions or vice versa.

And Adobe products started from movie industry where film was scanned and each frame was manipulated, and then re-exposed again for distribution to movie theaters. It as well got quickly to photoshops where printing was done. So print industry and scannin industry used it a lot, that lead to confusing use of "Resolution" and image size as physical dimensions.

While image processing, storage etc is done without physical dimensions and with pure data as resolution, where individual pixel is smallest value digitally stored.

In a nutshell, one works with either physical dimensions and needs to use a multiplier called "resolution" to translate between physical media, like "I scan this postcard (A6) of 148x105 mm at 300 PPI, and when I print it at 300 PPI, it will come out on paper as size of 146x105 mm. If I instead use 150 PPI then print size is A5 as it will be double in size, so dimensions are twice larger 210x148 mm and surface area is four times larger. And it will look as good so on twice further viewing distance.

Why one might want to set a specific DPI/PPI value regardless physical dimensions but without changing resolution? Because they are taught to "300 DPI is high quality", but it is multiplier to resolution to inform what is input/output dimensions values.

 

 

[Poziomka]

Hi,

I agree with eadauto

Please add a resolution option for the pixel formats export.

Let me write why.
I am working on a Press Ready project; the default resolution is 300ppi and it should be like that. But I also need to prepare a tiff of the same size but 150ppi.
Normal export sets the resolution to that declared in Affinity Designer, i.e. 300ppi.
The export takes longer and I still need to open the file and change the resolution.
Simply it would be faster.

[Andy05]

On 8/12/2020 at 6:19 PM, Poziomka said:

Hi,

I agree with eadauto

Please add a resolution option for the pixel formats export.

Let me write why.
I am working on a Press Ready project; the default resolution is 300ppi and it should be like that. But I also need to prepare a tiff of the same size but 150ppi.
Normal export sets the resolution to that declared in Affinity Designer, i.e. 300ppi.
The export takes longer and I still need to open the file and change the resolution.
Simply it would be faster.

That's only true, if you work with images in a given physical size for output (i. e. millimetres). If you stay in pixels, the DPI don't matter at all. 1000x1000 pixels are 1000x1000 pixels, no matter if you "assign" 10dpi or 10000 dpi to your image.

Your image neither will get bigger nor smaller by changing its dpi—unless you also resize its physical dimensions (amount of pixels).

[Fixx]

It would not hurt and actually help in some uses if user could change nominal DPI when exporting. 

[Andy05]

6 hours ago, Fixx said:

It would not hurt and actually help in some uses if user could change nominal DPI when exporting. 

When exactly is that relevant? The dpi are automatically determined during print if you print 1:1. And if you override this by changing the size the "preset" dpi change anyways. 

Exaggerated example, to prove my point. Create an image, 100 x100 px. So a very, very tiny one with very little details. Now, "assign" 3000 dpi. That should print 10 inch x 10 inch with 300 dpi. Try it again, with 10 dpi assigned to the original image and print it at the same size. Now what? Exactly, the quality is the same. The quality is still crap, no matter what amount of DPI you setup for the input image as long as you don't edit the amount of pixels, too. BTW, both images have been printed with 300 dpi in this example—given that's the native resolution of the printer.

I don't know why so many people think that assigning some dpi to a PIXEL based image has something to do with the quality. 

[fde101]

1 hour ago, Andy05 said:

When exactly is that relevant?

The only use case I personally can think of for this is to simplify the process of importing the image into another application which relies on the DPI information to control the initial placed size of the image within a document that contains other elements.

[Fixx]

4 hours ago, Andy05 said:

When exactly is that relevant?

When I send picture to a print service I can order "Place this picture in the middle of 70X100 Hahnemühle German Etching 310 gsm paper, except place extra 4 cm in the bottom part" and I know I get it printed right. I just did. It IS useful. I do not have to tell them "Oh yes, scale the image so and so and leave such and such margins".

And yes, it helps to have imported images ready 300 dpi in layout apps. It really makes handling them easier.

[Andy05]

But even then—the size of the output is NOT connected to your dpi settings rather than by the image's pixel dimensions. Its size is determined by the document's dpi settings where your image is placed in. That's the difference. But then again, the document's setup will just override your lovely dpi settings for your image. If they print images without size information, they will get printed in different sizes, depending on the printer's resolution.

Just try it - and you'll see. Use an image 1000  x 1000 pixels and set it to 300 dpi. Then again use an image 1000 x 1000 at 30 dpi and print both of them. Both will print at the same size if they are sent directly to a printer (without getting placed into a document or unless your software or printer driver does some funny stuff like resizing images for output in order to correct the wrong thinking about dpi settings—some consumer grade printers do that). DPI settings without dimensions of an image (not pixels) mean nothing. 

fde101 mentioned the only point I can think of why dpi settings for an image might be helpful. Because they determine how big an image initially will show up when you import it into your layout software/document. 

[fde101]

1 hour ago, Andy05 said:

the size of the output is NOT connected to your dpi settings

Actually, you just brought up another interesting point:

[Andy05]

2 minutes ago, fde101 said:

Actually, you just brought up another interesting point:

That's what I meant. Your printer driver scales the image on its own. So it's actually rather dangerous setting up some dpi with your image. It's upscaling a 72 dpi image and downscaling if "dpi in image" > printer's resolution and prints either with XXX dpi (whatever resolution your printer has).

That's why professional printing demands a combination of size and dpi. Not pixels and dpi (latter is just wrong). Otherwise you don't have any control about the output, it can vary from printer to printer.
 

[fde101]

10 minutes ago, Andy05 said:

size and dpi. Not pixels and dpi

Ok, that one doesn't make any sense.

Practically all raster image formats store pixel and dpi regardless of what physical size units you have selected in the program you used to create them.  They don't know anything about inches or millimeters.

Also, the image I used to demonstrate was created with pixels as a unit and the print system still responded to the DPI setting in determining the output size.

And no, the driver did not determine that scaling - it is in this case a function of the Affinity Photo application, before it reaches the driver, and so would be the same for any printer.

[Andy05]

It makes perfectly sense. Read my comment again. I talked about printing, not storing/saving images. You can save whatever dpi with your images, these setting change instantly when you chose the size of your output or when you place it in a document (this needs to have dpi settings for the desired output, not your image). It really doesn't matter, if you save your images with 10 or 100000 dpi. The quality doesn't change at all. The only reproducible combination for printing is size and dpi, if your want to have consistency. And that's something—as you mentioned yourself correctly—which can't be stored in an image itself. That's what I'm telling here all the time, and that's the reason why dpi settings in images are pointless.

You assign dpi for output to a document where you place your image into. Or—in your example—your app or printer driver does this job for you when you print it (therefore the different sizes despite the same amount of pixels in both cases). Hence, having some weird combination of dpi and pixels creates unpredictable results, if you use different apps and/or printers when printing your image. You basically proved my point.

You always should set the size when printing. Either by overriding your apps/printer's scaling when printing or within the document you place your image in.

 

EDIT: I deem the creators of graphic software (yes, you too, Adobe!) guilty for this misunderstanding. And it's their fault that the customer services of printing services have to deal with scenarios like "Why did you print my image on the back of my postcard so blurry?????? It had 300 dpi as you requested! I assigned it correctly in photoshop, I just checked it!" — "Yes, but the image had only 150x75 pixels." ;-D

[fde101]

6 hours ago, Andy05 said:

The quality doesn't change at all.

This is true; the DPI setting (and by extension the "physical" size of the image) is just metadata.

 

6 hours ago, Andy05 said:

size and dpi

"size" is a complicated word 🙂

I would argue that the horizontal and vertical pixel count is the truest concept of the size of the image.

That and the DPI are what get stored with the image.

 

6 hours ago, Andy05 said:

can't be stored in an image itself

The "physical" size of the image (inches, mm, etc.) is not stored because it would be redundant.  It is easily calculated from the pixel sound and dpi: 720 pixels / 72 dpi = 10 inches.

Some image formats do store DPI and some do not; those that do not cannot be mapped directly to a physical/printed size without guesswork by the application or intervention by the user.

 

6 hours ago, Andy05 said:

your app or printer driver does this job for you when you print it

It is always the application that establishes this, never the driver.  I can tell you that with quite a bit of certainty, having written printing code already for Mac applications I had started developing a while back.

 

6 hours ago, Andy05 said:

dpi settings in images are pointless

In general I tend to agree with this for most use cases, and have tried to make this point myself previously on the forum; however, there are a few users around who produce images from CAD software which are designed to be printed to a very specific scale.  Storing the DPI information in the images allows them to be placed within layout software while maintaining that correct scale for printing - it is apparently quite important to them, so there are at least a few edge cases like that in which the DPI value in the image clearly is not "pointless" but serves a meaningful function for those users.

Another potential use case would be in the printing of maps, as many of these are designed to be printed to an exact scale, and there are even special rulers around for working with maps printed at a few common scales (ex. https://smile.amazon.com/Pocket-Sized-Slot-Tool-Rectangular/dp/B005CS2EW2/), which again would require placement and printing of the image with a very specific size.

Yes, they could manually work out the scale and redo it in the layout application... but why reinvent the wheel when the computer can do it for you, particularly when precision counts?

[Andy05]

I'm not into CAD, so can't say if those programs benefit from wrongly defined "dpi settings" in images.

But seriously? The layout for such a precision/map tool? I highly doubt that anyone reliable would create such scales on a per-pixel base. Maybe for some Chinese imports. I refuse to accept that those scales are created as images. I'm pretty sure, they are vectors.

[Poziomka]

On 8/16/2020 at 7:12 PM, Andy05 said:

That's only true, if you work with images in a given physical size for output (i. e. millimetres). If you stay in pixels, the DPI don't matter at all. 1000x1000 pixels are 1000x1000 pixels, no matter if you "assign" 10dpi or 10000 dpi to your image.

Your image neither will get bigger nor smaller by changing its dpi—unless you also resize its physical dimensions (amount of pixels).

I just wrote about it.
In print, press ready projects, the units are in millimetres, inches, picas, points, but not pixels! The customer is not interested in how many pixels it has vertically and horizontally, only the size for printing and the appropriate resolution.
So, after exporting to tiff, I will get the image in the size declared in the project and resolution of 300 ppi. The client needs 150ppi and I have to redo it. And that's only why I'm writing about it.

[Andy05]

32 minutes ago, Poziomka said:

I just wrote about it.
In print, press ready projects, the units are in millimetres, inches, picas, points, but not pixels! The customer is not interested in how many pixels it has vertically and horizontally, only the size for printing and the appropriate resolution.
So, after exporting to tiff, I will get the image in the size declared in the project and resolution of 300 ppi. The client needs 150ppi and I have to redo it. And that's only why I'm writing about it.

What? If you have the "image with 300 dpi", why do you (or your client) need it—again—in half of that resolution but with the same details/amount of pixels? Seriously, are all here printing just images directly from app to printer and rely just on what HP, Brother, Canon or whatever printing service decides what to do with the dpi in regards of output size? No layouts done here whatsoever? Unless you don't tell the printer/printing service what size the output should be, the "dpi settings" in your image are noting but decoration. As you mentioned yourself: You need to tell the size in millimeters, inches etc. 

Images are usually placed into a layout for printing. And if you seriously just print images directly, you at least determine the size of the output either in the app's printing dialog or in the printer's. If you "assign" 150dpi to a "300dpi" image, all you achieve is an automatically resized output of the image, which fde101 proved with screenshots above. Depending on your client's setup, this size won't even the same as you intended. 

"But it works this way for you thus far?" Good luck with your workflow then, if your client purchases a different printer or uses a different printing service. How will you explain to him if the images don't print in the same size on his the configuration despite your "perfect dpi settings"?

 

[Poziomka]

On 8/19/2020 at 8:49 PM, Andy05 said:

What? If you have the "image with 300 dpi"

This is the problem! This is not an image but a vector!

Project made in Affinity Designer. Most of the layout is vector graphics and text. There are also 300ppi illustrations. Ultimately, I generate pdf, but at the client's request there should also be a 150ppi image and that's it.
Basically, the post was supposed to highlight the lack of resolution selection when exporting to an image from Affinity Designer or Publisher! And the export module is the same in all Affinity applications.