Efficient way of calculating design dimensions based on print DPI

[Billy385499119sr8]

I have recently got my first job at a design and marketing company where most of their clients are builders, developers and architects. My work here as designer is designing property brochures.

Now the company CEO to save the printing costs to the company has asked my senior to decide which of the pages in brochure can be printed at a lower DPI. Usually the pages that have smaller images and more text get printed at lower DPI.

This surprised me initially, but upon asking my senior, he told me that printing pages at lower DPI means less ink usage and hence discounted printing for the company.

Now, brochures are of a lot of different sizes like 11' x 17', 9' x 12', and 11' x 25' being the most common one at our company.

So I have to calculate the dimensions for the each brochure pages in pixels based on the PPI and then design and export them at the correct DPI setting. Then I have to create batches of files based on the DPI and send them to our printing partner for printing.

Calculating the correct pixel dimensions repeatedly and ensuring their accuracy is quite stressful, and my senior has emphasized that there's no room for error as it could result in blurry prints.

I don't want to make mistakes at my first job. Is there any feature in InDesign that can help me do this more efficiently and accurately? Currently, I'm using my phone calculator to find dimensions.

[Eugene Tyson]

Well - bluntly - this sounds ridiculous. 

This approach sounds quite misguided.

DPI (dots per inch) is determined by the output device and the printing method used.

For instance, in lithographic printing, different LPI (lines per inch) settings lead to varying results. Newspapers typically use coarse paper, which absorbs more ink.

To calculate DPI for lithographic printing, many people mistakenly use double the LPI. However, this isn't entirely accurate because halftone dots are rotated 45 degrees, impacting the effective measurement.

Using the Pythagorean theorem, where A^2+B^2=C^2 , the diagonal measurement yields a factor of about 1.41.

The actual number to multiply by is 1.41 - which is harder than just x2 which is why people use x2

For Newspaper printing - the LPI is set quite low - which is around 80-120 

For newspapers then it's 80x1.41 = 112.8 dpi up to 120x1.41= 169.2

And you'd need to ask your newspaper what their LPI is 

Magazines could use 120-150 = again multiply the LPI by 1.41 to get the optimal DPI

This is where the magic 300PPI or DPI comes in for print
It's a simplification of the 150 LPI output at x2 = 300 

And that's why people say it must be 300!!!! 

High end coffee magazines etc could use 175-200 LPI 

So you're limited by the output device LPI in Lithographic Printing

For digital printing, it's a bit more forgiving in a sense
You could go below 225 as low as 200 or even 175

When dealing with various types of images such as grayscale images, line art, and bitmaps—different DPI considerations apply. Line art, for example, typically requires higher settings in around the 1200DPI to maintain sharpness, while grayscale images might vary based on the desired print quality.

You could have a foggy scene or photo and where your LPI might be 150 on the output device - and you set your image to 211.5 DPI - that might not be necessary - you could go lower for foggy images, or images which are not very sharp - even to 150 or 125 DPI

Then you have large format printing - you typically don't need 300 DPI for billboards - usually 30DPI is fine for billboards.

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All that being said -  you won't know what DPI to make anything until you ask the printers what LPI their devices use (if they even know) - given for Litho it's usually 150 - then you are safe around the 225 mark or 250 or 300 - 

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Finally - INDesign you can select your DPI of images when exporting  
In the Compression Settings for the PDF

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In short
Ask your designated printer what DPI is optimal - and set your compression settings to suit the PDF export.

[Billy385499119sr8]

Thanks for the reply. Yes, I know that at the time of export we can set the PPI and select compression type. But calculating the dimensions in pixels when starting the project based on the size of brochure page is what I am concerned with.

And, yes I understand that billboard prints are good even when printed at 30 DPI since they will be viewed from a distance and magazines or anything that would be viewed from a hand's distance should be printed at higher DPI.

Most pages of the brochures I create are printed at 300 DPI, but some are even printed at 250 and 275 PPI. Since these are printed in bulk probably in hundreds, our company is able to save on cost. I don't exactly know how costing works with our printing partner. I am just doing what I am told to do. 

Here I am concerned with calculating the dimensions between pixels and inches of the page based on the PPI that page is to be printed. 

In simpler terms, I am just looking for a feature in InDesign that shows me the size of the page and elements (to check if they have the required resolution) in inches and pixels together, either when hovered on or by any other way.

I don't know why this is so complicated.

For the software that's been created to design for print this should be at front or very easy to find, if available at all!

[Eugene Tyson]

I'm confused why you need that. 

The conversion InDesign does for PPI downsampling is the exact same as the downsampling done in Photoshop.

So I have to calculate the dimensions for the each brochure pages in pixels based on the PPI and then design and export them at the correct DPI setting. Then I have to create batches of files based on the DPI and send them to our printing partner for printing.

By @Billy385499119sr8

This is really confusing 

PPI and DPI are correlated 

10 inch brochure at 300 ppi  = 3000 pixels

10 inch at 250 ppi = 2500 pixels

I'm not sure why you need Pixel based dimensions for the pages.

You only need the final print size of the brochure - which should/could be in Inches/mm 

Then you drop your Images into InDesign as links.

You see at the bottom of the image it shows EFFECTIVE and ACTUAL

So at 100% it's size it's actually 300ppi

But it's scaled (reduced) which brings up the Effective PPI to 311 PPI

So the image is scaled to 96.46% (300/311*100)

In short

Your document should be at the output size and final size of your Print Dimensions in inches or mm etc. 

You don't need pixel based dimensions for your pages 

When you use File>Place and insert the image you can see directly in the Effective PPI what the image size is in PPI.

Then on export to PDF you can reduce all images to the PPI you desire for printing. 

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Or I'm probably missing something here.

 

[Floid38571765bmv9]

Seems like you or your company are following not necessarily a wrong but a unique process and your CEO has found a great way to increase profit for the company. Nothing wrong.

I would suggest you to discuss this with your senior probably during non work hours. Since you are at very early stage in your career no one should mind asking you questions.

Also there's no need to use your phone's calculator for doing conversions manually. There are various calculators available online like this one that would make your job slightly easy.

But just like everybody else, I am also not getting why you need to find the dimensions in pixels when InDesign allows you to enter it in inch and other units. Also the software allows you to set the PPI for final exports, including for images.

If it's about entering the data in the excel sheet that your company manages for record, then there as well you can add formula to the cell and it will also do the calculations automatically. 

[rob day]

Yes, I know that at the time of export we can set the PPI and select compression type. But calculating the dimensions in pixels when starting the project based on the size of brochure page is what I am concerned with.

Hi @Billy385499119sr8 , InDesign and PDF pages are vector objects they have no resolution. A page can include an image object, which would have a pixels per inch (PPI) resolution, but those pixels are not output they have to be converted into a halftone screen (offset/laser) or a stochastic screen (inkjet). It’s the halftone/stochastic screen that gets printed, and the print device sets the dots per inch (DPI) used to draw the screen and set the ink/toner density—you can’t do it from InDesign.

[BobLevine]

Eugene is right. I'll resist the temptation to expand on it.

[Eugene Tyson]

I'd welcome it

I skipped some parts in trying to simplify it.

Expansion is good 

[SimonBarton]

Having worked in the design and print industry for over 20 years, the past 10 of which have been spent in a printing company I genuninly don't understand the the logic behind what you've been asked to do nor how it could result in a significant discount on the print costs.
During pre-press process your files will be RIP'd at the optimum settings for the press regardless of what resolution you've created them at and only bitmapped images have an effective resolutions. Text, gradients and graphics created in Illustrator are all vector elements and ignore the output resolution of your pdf settings. 
If you've been supplying files for print with hundreds of very large image files which are scaled down to a thumbnail size in your Indesign documents it's possible that when the printers are running these files through their pre-press software its taking a very long time to process and therefore they may have offered a discount as an incentive for your company supply lower resolution files but they won't be running different pages in a brochure at different settings unless perhaps they are printing the covers on a different paper stock.
It sounds to me like your CEO and Senior have either misunderstod what the printers have asked or it's the equivelent of sending you to the hardware store for stripped paint or a long wait.

[John D Herzog]

I was thinking it might be hazing as well. I cannot see how changing the dpi will change the ink coverage. the amount of ink will be set at the printer regardless of the dpi of the file. It just determines if file pixels will be seen in the print. I also agree it is probably a discount for rip time. I have worked 19 years in prepress/press operation for a printing company.

[James Gifford—NitroPress]

As noted in prior comments, this is a very confusing set of claims. At a technical level, DPI has nothing much to do with print cost; it matters only when a more costly process must be used to achieve a higher DPI result. Which doesn't quite align with what you say the issues and goals are.

For one thing, printing part of a brochure on one line and other parts on other lines is almost certainly going to be more expensive in marrying, binding and trimming the result than just "hitting print" on a single print line. I've done a lot of work in this general realm, and unless you're leaving out some critical aspects, it sounds as if your CEO has some faulty ideas about how printing works, and you're not likely to come up with a solution that reduces costs (much, if at all) by trying to use such a complex print workflow.

I'm sure the expertise here can help with the technical issues of achieving the (technical) goal, but someone in your food chain should really work through the actual print costs for the various options to see if all the effort (now, in working out the methods) and down the road (in splitting up and managing each project with this complex print process) actually saves any money, or at least enough to pay for all the man-hours it will take to execute them.

TL;DR version, which a new employee on his first job really can't use, boils down to "Boss? Ya gotta be kidding, right?" 🙂 But that's far too common in firms where the brass has erroneous ideas about how a production process actually works. So gentle, humble, fact-based reporting back up the chain might be the right approach.

[leo.r]

Usually the pages that have smaller images and more text get printed at lower DPI.

...

So I have to calculate the dimensions for the each brochure pages in pixels based on the PPI...

By @Billy385499119sr8

I can only agree with the already expressed opinion that it all sounds bizarre.

For example, as others also noted, why would your bosses ask you to calculate pixel page dimensions for pages that contain both images and text? This could, potentially, make sense if they wanted to convert entire pages into images. Which isn't the goal here, obviously.

[Robert at ID-Tasker]

I think it has something to do with the EU directive - can't give any more details, just that someone some time ago asked about such calculator - that "taxes" printed materials based on how much ink was put on those materials... 

[Billy385499119sr8]

Thanks everyone for your replies. I will research more about my problem and if I still don't find the solution to my problem, I will talk to my senior.

[Eugene Tyson]

Might be another approach to send the print specs and quantities to another printers and ask them what they think about price and reducing costs etc.

I would suggest talking with a Print Broker rather than dealing with print companies individually. 

[rob day]

I will research more about my problem

This thread is a good example of why Adobe explicitly defined their terminologies for different kinds of resolution back in the early 90s—PPI, LPI, and DPI.

Image resolution is referred to as PPI, not DPI, and that usage is consistent in all of the Adobe print apps. For all commercial printing methods, pixels are not output—image pixels have to be converted by the print driver to a screen (LPI), and that screen is drawn with printer dots (DPI). Changing an image’s pixel resolution will have little affect on the output halftone dot sizes. It’s the screen (on the right in this simulation) that is output, not the pixels:

[Peter Spier]

I guess I'll pile on here as well. I don't think anyone has pointed out that reducing the DPI just makes the dots larger, so they are not using any less ink.

I suspesct @Robert at ID-Tasker is probably right that this has to to with page area coverage, but changing print resolution will have no effect on that at all.

[Robert at ID-Tasker]

Here is the thread:

https://community.adobe.com/t5/indesign-discussions/total-ink-coverage-plug-in-for-indesign/td-p/136...