Indesign sizing/resolution question

[keii24515601]

Hello

I'm trying to create a PDF document that has a 16:9 aspect ratio (up to full HD) and it will be viewed on screen only (won't be printed)

I started by creating a document that is 1920px x 1080px in InDesign. But the problem that I've just noticed is that this is a huge page size...if I change the setting to mm, it equals to 677.333mm x 381mm. When I opened a blank document in Photoshop as 300dpi 1920px x 1080px and convert to mm it's only 162.56mm x 91.44mm which is even more confusing. I know that it doesn't matter as I can just export the file as a PDF and it would look fine on screen, but I'm using images and they aren't big enough to go full page in this setting. It would have to be stretched out and then when I export it in the highest resolution it would still look pixelated because it was stretched out on Indesign.. does that make sense?

So my question is... how do I set an ideal format in Indesign when trying to create a PDF that's not going to be too small/too big? 

I normally only work in print, so this is all new to me and I have such a hard time understanding dpi and effective dpi...please help!

Thank you

[Eugene Tyson]

When I opened a blank document in Photoshop as 300dpi 1920px x 1080px and convert to mm it's only 162.56mm x 91.44mm which is even more confusing

By @keii24515601

Not sure what's confusing? 

300 Dots Per Inch (dpi) 

1920 x 1080 

1920/300 = 6.4 inches 

1080/300 = 3.6 inches

6.4 inches = 162.56mm

3.6 inches = 91.44 mm

1920px x 1080px in InDesign

Others will correct me on this - but this is my overly simplified version

InDesign operates in 72ppi - and your screen is not 72ppi

1920 px x 1080 px @ 72 - follow same format as above

1920/72= 26.6 inches 

1080/72= 15 inches

But your screen would be actually 92 or 104 ppi or something

I also think acrobat resolution can be set in the preferences

20 you should be working in slightly higher resolution

So increase your photoshop resolution to 92 or 104 or something like that

Ultimately it will rely on the display and the settings you choose.

But don't overcomplicate it. 

[keii24515601]

Hi, thank you for your reply.

With everyone's help I do now understand that Indesign is 72ppi.

I'm just still not understanding how for example I have an 72ppi image at 600px x 400px and I want to place it to fill say half of my page. On Indesign I would need to stretch that pic so that the effective ppi is less than 72 resulting in a pixelated outcome..

Also I never thought about my screen and now I'm even more confused haha 
Thank you all for your help

[Eugene Tyson]

Half  your page
1920px = 960px

1080px = 540 px

If your image is 600 x 400
then it's not half - scaling it up from

600 x 400 @ 72 ppi
to 960 x 540 would effectively make it 45 ppi

[rob day]

With everyone's help I do now understand that Indesign is 72ppi

No, InDesign pages have no resolution —the page is a vector object not an image. You are being confused by the Pixel Ruler unit which is a simply a static output measurement.

Placed images do have a resolution which can be anything. When you scale a placed image its pixels are scaled along with its output dimensions (the Effective Resolution). A 5”x7” image at 300ppi would have a 1500 x 2100 pixel dimension If you scale the image by 200% the pixel dimensions don’t change, but the size of the pixels are scaled up by 200% and the effective output resolution is now 150ppi—the pixels were 1/300”, now they are twice as large at 1/150”

[Eugene Tyson]

That was my fault. I over simplified and reading back it's not what I meant at all. 

[keii24515601]

ohh I see I understand. I just tested different dimensions but keeping the same ratio and it turned out the same... so I guess I don't need to change my document. Thanks for your help

[D. Schulte]

When you work in InDesign and create a digital document in a pixel format it uses 72 ppi (pixel per inch). Thats why it is so big when you convert it to mm in opposite to if you created the same document in Photoshop using 300 ppi and then converting it to mm. Have in mind that when you create a pixel format the ppi does not really matter. You have A x B pixels, the size will always be that. The ppi defines how this pixel format will be displayed when working in mm or inch which you don't do. So don't worry – 

Whe you place images and know their size is big enough, try checking the files in Photoshop regarding their set ppi. When you set them to 72 ppi (without changing the actual pixel format!) and place them in your digital document in InDesign you should be fine.

[keii24515601]

Hi, thank you very much for your reply.

That makes sense that the pixel format uses 72ppi and that's why it's so big.

I have my link panel in Indesign set to show "Actual PPI" and "Effective PPI". The images I'm worried about are when the actual PPI is 72 but effective is less than 72. They're now being stretched because the document is so big so they look pixelated...

[rob day]

Also, Pixels in InDesign are an output Ruler Unit (1/72”) not a measure of resolution—an ID page has no resolution.

The Pixel unit is useful when the Export is to an image format—JPEG or PNG. An Export at 72ppi will result in an image with matching pixel dimensions. PDF is a vector format, so there isn’t much advantage in working with Pixels when the Export will always be PDF.

[keii24515601]

Hello

Thank you also very much for your reply. So if your export will always be 16:9 aspect ratio PDF for screen, what would you use to set up your document? Sorry if I'm repeating myself but I'm still struggling! 

[James Gifford—NitroPress]

The short answer on top of all the prior information — the best of which is Eugene's 'don't overcomplicate it'! — is that a 16:9 layout is paramount, a reasonable amount of resolution for any raster images is probably enough, and the vector nature of all else, including type, passed through PDF, will generate all the image quality you need. (I've done many, many HD presentaions using ID/PDF, since I loathe PowerPoint.)

The only area really needing any extra thought is in images — raster images, photos — where you want maximum screen quality. As long as your source images have an effective PPI of about 200 or more (and ID tells you effective PPI in the Info panel), you probably won't have any issues regardless of how large a screen the pages are displayed on.

Other than that, don't overthink it, don't overcalculate it and don't overcomplicate it. The tech handles the details very nicely in this case. 🙂

[Eugene Tyson]

Yeh - like there's no need to resize images in photoshop - just place them in InDesign and scale them - as long as the effective resolution is roughly over 90ppi it should look good on screen - as acrobat can have it's own resolution setting.

Anyway - it's a presentation - viewed from a distance - so it should be fine. 

[keii24515601]

Yes, that makes sense - Thank you