How do I convert 72dpi to 300dpi resolution image?

Posted on 2007-08-04
Medium Priority
Last Modified: 2013-11-19
I have an image that is 72dpi resolution but want to put it in a print catalog. Is there any posisble way to recreate the image in 300dpi resolution with some feature in Photoshop? Even if I have to use another software, I really need to do this somehow. Thanks in advance.
Question by:bemara57
LVL 13

Expert Comment

ID: 19632652
No. While you can reduce the resolution of an image through software, increasing it is another story. Even if it can be done via pixel interpolation, the result will basically be a larger file, but with no extra detail. In fact, it could look washed out or muddy.

Tip. Always start with very high resolution images and reduce for your needs. Starting with something small and trying to increase from there will yield poor results.
LVL 11

Assisted Solution

by:Tom Ray
Tom Ray earned 400 total points
ID: 19632677
yes you can, however, is final physical size going to be big enough?

for example, if you have a 10 x 10 photoshop file at 72 dpi, and you want to make it 300 dpi and keep the quality, then you will sacrifice physical size. after the conversion you'll have a 2.4 x 2.4 photoshop file at 300 dpi.

to follow this example, open photoshop and create a new 10 x 10 document at 72 dpi. then under "image" pull down and select "image size..." here you'll see that the file is indeed 10 x 10 and 72 dpi. notice the 'resample image' checkbox in the lower corner. you'll need to uncheck it, notice that the 'proportion link' is now locking in on both size and resolution. now type in your desired resolution (300). see how the physical size of the file is lowered? however, if you were to go lower on the resolution then the physical size goes up.

in this example if 2.4 x 2.4 at 300 dpi isn't sufficient, then chances are the best alternative is to have the image re-scanned at a better resolution.
LVL 26

Accepted Solution

David Brugge earned 1200 total points
ID: 19633431
So far we have a no, and we have a yes.
I say no and yes.
Answer 1:
Yes, you can always tell Photoshop to spread the pixels apart, add three more pixels in each directions and take a wild guess at what these new pixels would look like, but you are only adding pixels, not any additional detail about the image.
Answer 2
No, it can't be done. This is the cold slap of reality. I am forced to do this many more times than I wish and I always groan because you end up spending hours of work with very little to show for it. If the image will sit by itself in a page layout program like Quark or InDesign, Up scale it to 144, sharpen just a little, tweek the contrast if needed, and hope that you never have to do this again.

If it is a component in a 300 dpi image and has to be enlarged to fit, try this trick. Figure out the final size of the image in pixels and make a note.

Now select Image > Image size and change the resolution to 300. Press Okay.

Again pull up the image size dialogue and this time, set the width and height to 110%. Check all three check boxes, and set Resample Image to Bicubic Smoother (Always use smoother when upsampeling and sharper when downsampeling) Click okay. Now apply a slight sharpening.

Do the last two steps again, always going by 10% and watching the image size as it approaches the target size. When you get to where 10% will go over the target size, change the width and height to the target size (again use bicubic smoother) and press okay.

The technicians at Adobe claim the upsizing by increments of 10% allows the Photoshop algorithms to make their best guess at filling in the missing pixels.  Tis, by the way, is an excellent time to learn how to make an action that does repetitive tasks for you with a single button click.

At the very best, you will end up with a picture that's a little more blurry than the rest, at the worst, you waste a lot of time and end up with a picture that's a lot more blurry than the rest.

Best of luck to you,

David B.
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Expert Comment

ID: 19651030
Image>Image size> 300 dpi> bicubic> ok.  Voila

Expert Comment

ID: 19651037
I wouldn' assume poor quality until you have tried.  I have a camera that shoots professional 30mb photos at 72dpi.  They are just big photos.  It doesn't mean the quality isn't there just because the image is 72 dpi.  

Expert Comment

ID: 19651041
Did you shoot these with a digital camera?   What model?  Megapixels?  Tripod?  
LVL 11

Expert Comment

by:Tom Ray
ID: 19654940
>I wouldn' assume poor quality until you have tried.  I have a camera that shoots professional 30mb photos at 72dpi.  They are just big photos.  It doesn't mean the quality isn't there just because the image is 72 dpi.  

yes this is absolutely true. then if you apply the method i've outlined, you'll see what size the photo would be at 300 dpi, or what percentage to place a photo in order to achieve 300 dpi.
LVL 11

Assisted Solution

walkerke earned 400 total points
ID: 19687340
If the 72dpi photo is very sharp without adding sharpness artificially, a Photoshop plugin called Genuine Fractals can do some amazing things with regard to increasing the resolution. It's very important, though, for the original image to be naturally sharp. Adding sharpness in Photoshop before increasing the resolution in Genuine Fractals causes artifacts to appear in the image.

I have successfully taken an 8x10 300ppi image to 24x30 300ppi with little, if any, pixellation using Genuine Fractals.
LVL 31

Expert Comment

ID: 19694873
Hi bemara57

you have lot of advice here and this all makes sense in its own right but only more or less if you look at you intended use. You want to print this image and you need to provide your printer 300dpi CMYK colour balanced images for it to look correct in the catalog.

The image that you have will have a certain dimension in pixels but also a size in inches or mm's or whatever you work in. Your printer file will require an image in a certain size, it does not care about pixel dimensions, so in that sense anything is convertable it may just look rubbish.

If you do bicubic up sampling then you allow the Photoshop apps to fill in the pixels one up one sideways effectively creating 4 pixels from each, giving you 288dpi as a straight conversion. This will be fine for printing albeit that a flight checker will flag this. If you instead choose 300dpi then you will get scaling errors , although Photoshop distributes the errors among all the pixels.

Bottom line is you will need to see how the final print size compares to your picture size. If you have taken a picture in large format then you may be able to resize to your printsize and have no trouble upsampling. If your pic size however is in the same size that you need to print you will NOT be able to upsample whatever plug-in you choose or sharpen filter you apply as this may fool the eye on a display but will show up low-res when printed.

Rule of thumb is if the picture is twice as high and twice as wide in its current size than the printed (needed) size then you be most likely fine. If it is anywhere between this and same use D_Brugge's advbice and make a judgement call on the outcome. IUf it is same or less don't bother you be disappointed printing it.

Genuine Fractals cost $160 but is a great tool to make your images look less blurry on upsampling if you follow walkerke's advice, but will not perform wonders either. Simply, if the information is not in the pixels you cannot create it with a tool.


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