PDA

View Full Version : Best upscaling method?



Etch
01-01-2009, 10:13 PM
So I'm working on this image I sketched up the other day and decided I'd like to print it off as a 22.5"x36" poster. Only problem is I've already started it at a much smaller size and my computer doesn't have the power to manage a 6750x10800px image with all it's layers and stuff. The file is already almost 1.7gig when opened in the gimp and I only have like 4 layers.

So basically I've theorized a few different solutions to my problem but I'd like to here from those more knowledgeable. The image is totally 2d by the way so I cant just render it larger.

Method 1
Just scale up the image. Quality is still okay but I'd still like to do this the right way.

Method 2
Scale the image up way larger than I need it to be then print it at a much higher dpi.

Method 3
Print the image at its current resolution and scan it in at something over 800 dpi.

So which of these three methods, or ones I didn't even think of, would you guys use to upscale an image and end with a presentable quality.

Captain Obvious
01-01-2009, 11:32 PM
Use Photoshop instead of the GIMP, maybe? It handles significantly higher resolutions, and is generally more better. For upscaling, you could try Blow Up (http://www.alienskin.com/blowup/). It works by vectorizing the image, and then rasterizing it at a higher resolution. Results generally seem quite good.

Also, I really don't think you'll actually need 300 DPI for a 22.5 by 36 inch poster. You can probably get away with 100 DPI or so.

JonW
01-02-2009, 12:31 AM
Firstly, how sharp it is will be depends on what you have to play with.

Assuming you have roughly an A3 widths worth of pixels at 300dpi, about 5000. When this is printed out at 900mm wide it will be 140dpi, this will be more than adequate for a poster. If its an A4, its about 100dpi, this will most likely still be ok depending on the subject & depending on the quality of the image to start with.

If you have some plane text, this should be separate from the image. Do the text in Illustrator of similar and drop the image into here and create an EPS file. If you are doing it on your own printer you may be stuck with Photoshop and to get sharp text will have to res up the image. Get rid of any layers that are absolutely not required, even do the text in a new file if its not covering the entire image and at the last moment drop it onto your image when its ready. Flatten a copy of the image before printing.

Desperation..... Lower Photoshop Cache to 1 for this job, easy, this only affects display quality. Close every other application to free up ram. If you are on a PC you can close a lot of the processes to free up more ram, Control Panel - Administrative Tools - Computer Management - Service and Application - Services , Look at properties on each item & in “Startup type” you can disable a lot of what is running, ********but be very very careful & read the Description “extremely carefully” before you close things. ********

Now with the extra ram....

Give the image a bit of extra large diameter sharpening. Say Amount 10 to 20% (very low), Radius 20 to 50 (very large), Threshold 0.

What you are doing here is not so much sharpening the pixels but sharpening the contrast.

Just resample the image to suit the new dimensions

Before you print the image, print a test strip or two or a patch from the image & mount it on the wall & view it from the same distance the the large image will be viewed from. Its pointless pixel peeping at 300mm when its not going to be view from this distance.

If you are printing at a bureau speak to them.