Upscaling an image from 72 - 300dpi

[devswap]

Before I begin, please can I say I am not a print guy but a web guy helping to reproduce a brochure so please dont expect print knowledge. I recreated a brochure in indesign and all was fine until the printers reported that the images were pixellated. I checked what had been inserted and I had been given hi res files. However these files were 10000px wide but 72dpi. The printers asked for images at least 300dpi. The source of the images advises just editing the image in photoshop to make it 300 dpi with resampling turned off. They said that the image is physically massive at 72dpi and would just reduce in size making it 300dpi but would still be plenty big enough for an A4 print. I have done this and output the pdf but the image quality on screen in both pdf's ie the old 72dpi and the new 300dpi look identical. My question is, is it possible to convert a 72dpi image to 300dpi or is my instinct that says you cant add extra detail to something that doesnt have detail magically and we should be starting with a 300dpi image from the start. Welcome your thoughts, i will post this to the indessign forum too as it bridges the two apps.

[jane-e]

When you look in the Links panel, what does it say for the "Effective PPI" (Pixels per Inch)?

~ Jane

[hammer0909]

Hi devswap,

I know this topic can get very frustrating for a web guy going to print or a print guy going to web since we look at resolution in different ways. Your image that is 10000 px at 72 ppi would end up being about 33 inches at 300 ppi. Plenty of resolution and this is why they both look the same after you make the adjustment because they are the same! 😉 Even if you leave the image as it was, you should have plenty of resolution in the file output from InDesign unless the quality is very poor to begin with. How does the file look visually? Good? I'd be happy to take a look at the image for you if you care to share a link. Jane-e provides good advice though. What is the effective resolution of the file when you click on it and view it in the Links panel?

[rob day]

The source of the images advises just editing the image in photoshop to make it 300 dpi with resampling turned off.

InDesign does the same when you scale an image. If you reduce the scale the image pixels get smaller relative to the output dimensions—which is the Effective Resolution listed in the Links panel.

Your 10,000 pixel image at 72ppi would have an output dimension width of 138.88 inches. You would have to scale it down to 6% in order for it to fit an A4 page, and the scaled output Effective resolution would be 1210 PPI

Keep in mind when you export to PDF, most PDF print presets will sample down images over 450ppi to 300ppi, so unless you change the default preset Compression setting, the 1210ppi image will get significantly down sampled on export