upconverting images to 300 dpi

[lowfreq]

I am in the process of submitting a paper to a scientific journal and their requirements are that images must be 300 dpi in either jpeg or tiff format.

The images supplied to me by the co-authors are all less than that, ranging from 60 dpi to 200 dpi.

how can I up convert these easily? The other thing is that the images are all on my work pc and cannot be removed from that machine.

thanks

 

[MacGizmo]

There is no way to "up convert" an image resolution. There are apps that can use algorithms to upscale an image by creating pixels that don't exist to fill in the gaps, but the quality is usually not very good.

DPI is misunderstood. You're 60 dpi image may actually be plenty of resolution if you're dramatically reducing the size of the image (which gives you an "effective resolution" much higher than the 60 dpi).

Also, I work a lot with science and medical journals... they are absolutely clueless when it comes to specifications like this and most likely don't even know what DPI stands for. One journal in particular that I recently worked with asks for 300 dpi CMYK images — the problem is that they weren't printing the pub, it was digital distribution via PDF (which means they really only "need" 72 dpi, and anything over 150 is pointless, and RGB is much higher quality than CMYK for on-screen viewing).

 

[Slartibart]

most graphic programs like Photoshop, Gimp, Graphicconverter, etc. have an option to adjust the dpi for an image as well as to choose an upscaling method.

 

[Herbert123]

Dpi is a meaningless value without referencing the dimensions an image should be printed at.

If your multitone colour or grayscale image is supposed to be printed at 50% DIN A4 format, that means the image must have a minimum resolution of 2480px by 1754px (plus a bit of bleed if running off the page, but let's leave that out of the conversation for now).

PPI (Pixels Per Inch) is used to denote image resolution, DPI when the image is printed.

8.267" x 300px = 2480px
5.847" x 300px = 1754px

Now you know how to calculate the minimum required resolution.

Your image should have that resolution and the ppi (not dpi) embedded parameter should be set to 300ppi (DO NOT resample after the right resolution requirements are met in your image editor - only change the internal PPI parameter!).

PPI by itself has no impact on resolution - only pixels do. What the PPI parameter does is tell layout software (such as InDesign) at what size it should be placed on the paper. That is it.

I could save a single pixel at 10.000 PPI and it wouldn't change the actual resolution of that one pixel. I could save a 10.000px square image at 1PPI and it again wouldn't make a difference to the actual resolution.

The single pixel with 300ppi embedded would be placed at exactly 1 inch square dimensions when imported into InDesign. (It translates to a printed 1dpi - 1 dot per inch).

This is why InDesign distinguishes between actual PPI and effective PPI: what is the PPI value embedded in an image file, and what is the actual ppi calculated by checking the image's resolution against the size that image is placed in the layout. The effective resolution should always be more or less 300PPI for colour and grayscale images.

For academic work often black and white imagery is placed as well. In that case the image should ideally have a minimum effective PPI resolution of 1200ppi - the above 1/2 A4 image would then have a resolution of 9920px by 7016px resolution. The reason for this is that black and white only does not need to be rasterized to simulated tints and hues by introducing dot patterns. These images should in principle ALWAYS be saved as TIFF. JPG is NOT suitable for these type of images.

So for black and white 1bit scans and images:

8.267" x 1200px = 9920px
5.847" x 1200px = 7016px

In short: never rely on DPI or PPI only - it is a useless unit to measure the actual effective resolution of a placed image. Always calculate the actual required pixel resolution at the size it will be printed at.

If unsure, inquire about the publication's layout/print size, and deliver images with an effective max resolution at the max size that these could be placed in the publication.
And @MacGizmo is correct in stating that many people working in the layout business have themselves utterly confused about what PPI/DPI means.

If someone asks you for 300dpi images, they have no clue indeed. They need to provide more information for you to decide what effective resolution your images should be delivered at. Which is why you need AT LEAST the final print size of the layout and how your images will be scaled and positioned on the page.

 

[wonderings]

If you have access to Photoshop you could load it there and just change the DPI to 300. This does not give you anything more or make your picture better but it should change the file so whatever is setting off warning bells on their end go off. I am assuming this is going to print? Printers RIP probably has default settings they want and this gets flagged in their preflight. Personally I would just let it go and get the job done.

You could install a demo of Photoshop, make the change, save and go about your day.

 

[chabig]

Preview can do that. Open the images and Export them. Select 300 pixels/inch as the output resolution. This can probably even be scripted with Automator so you can drag and drop for automatic conversion.

 

[organicCPU]

This can probably even be scripted with Automator so you can drag and drop for automatic conversion.

Without overcomplicate it, I'd suggest sips over Preview app for automatic conversion. Something like that goes into Terminal or slightly modified into Automator's do shell script part:

sips --setProperty dpiHeight 300.000 --setProperty dpiWidth 300.000 --setProperty format tiff --setProperty formatOptions lzw /path/to/image/source.jpeg --out /path/to/image/target.tiff

More info on this with man sips into Terminal. There is also a resampling function built into sips to scale the image. Although, I'd recommend Affinity Photo, Adobe Photoshop, Gimp, Krita or even a dedicated software like BenVista PhotoZoom Pro, AKVIS Magnifier AI, ON1 Resize or the free SmillaEnlarger for better results of blowing up image resolution.

 

[KeithCody]

Without overcomplicate it, I'd suggest sips over Preview app for automatic conversion. Something like that goes into Terminal or slightly modified into Automator's do shell script part:

sips --setProperty dpiHeight 300.000 --setProperty dpiWidth 300.000 --setProperty format tiff --setProperty formatOptions lzw /path/to/image/source.jpeg --out /path/to/image/target.tiff

More info on this with man sips into Terminal. There is also a resampling function built into sips to scale the image. Although, I'd recommend Affinity Photo, Adobe Photoshop, Gimp, Krita or even a dedicated software like BenVista PhotoZoom Pro, AKVIS Magnifier AI, ON1 Resize or the free SmillaEnlarger for better results of blowing up image resolution.

Thanks for this.