Hi-Res Photos from a zip file

Submitted by TylerR_NKY on Thu, 2008-07-03 19:46.

Member's Forum

So I was downloading a high-res photo from morguefile.com, and when I unzipped and opened the file the resolution was at 72. I went into image size and put it at 300 in Photoshop, and it looks fine. Am I going about this the right way or am I missing something?

Thanks

You don't get the idea

Submitted by Ivan on Thu, 2008-07-03 20:06.

You don't get the idea yet.

Resolution doesn't matter on screen. It only matters when you are printing something. Resolution alone doesn't mean anything, only paired with dimensions.

Imagine you have 1x1cm file with 300dpi and a 3x3cm with 100dpi. Both are exactly the same file.

By resizing a 1x1cm 7dpi to 1x1cm 300dpi all you are doing is making the image larger but it will be blurred. In effect you will have a larger image with the same amount of detail.

To put it short it doesn't make sense to re-size images to achieve 300dpi.

no matter what you do to a

Submitted by gwells on Thu, 2008-07-03 21:10.

no matter what you do to a file, you don't want the number of pixels to get larger.

so, as ivan said, if you have a 72dpi file that's 3000 x 3000 pixels, it shows up as 41.667 inches (he's in the US, ivan, so i'm gonna use inches... ;) ).

if you want to make that 72dpi, 3000 x 3000 pixel image 300dpi without having it be pixilated, instead of having a 41.667in x 41.667in file, you will now have a 10in x 10in file.

here's the math.

3000 pixels divided by 300 dpi = 10 inches.
3000 pixels divided by 72dpi = 41.667 inches

when you change resolution in photoshop and want to maintain the same number of pixels (which you should do, here), you need to make sure the "resample image" box at the bottom of the resize image dialog is turned off. that will ensure you maintain the 3000 x 3000 pixel image size, but change the resolution (and thus final printing size) of your document.

i'd like to recommend a really good book that will help you understand resolution. it's an old book (i bought it 12-13 years ago), but it still makes sense today. it's called 'Real world scanning and halftones" by David Blatner, Glenn Fleishman, Steve Roth, and Conrad Chavez. pretty sure it's been updated, since it says 3rd edition and i think mine was 2nd edition.

http://www.amazon.com/Real-World-Scanning-Halftones-3rd/dp/0321241320

So you're saying

Submitted by TylerR_NKY on Thu, 2008-07-03 21:43.

If I keep resampling turned off, changing the resolution will work for the quality of print?

I'll check that book out, thanks.

- thanks

Lets simplify it some more

Submitted by ireid on Fri, 2008-07-04 00:01.

If I have a 1 inch document at 72 dots per inch (DPI) for EVERY inch there would be 72 dots.

1 inch=72 dots (pixels)

NOW if I SCALE that up by 1 inch then I am INCREASING the size of the picture BUT NOT THE PHYSICAL AMOUNT OF DOTS (pixels). What I WOULD have is a 2 inch file at 72 DPI BUT the image would be blurry and icky because I am trying to add DOTS into an image that doesn't exist. Think of spreading out sand on a table. If I have more sand the more AREA I can cover. If I spread out the sand too much it will look spacey and weird (you dig?)

So the reverse is better. If I have 72 dots in 2 inch file and I REDUCE it by 1 inch then nothing is lost by reducing I COMPACT the dots further and the image would not LOOK blurry. (for lack of a better word)

So a 41 inch file at 72 dpi CANNOT be made BIGGER because there are no more dots to fill BUT if you REDUCE the size of the document then the DPI would go up as the physical size goes down (that's what we do when we un-check the re sampling box) If you un-check the box and type in 300 dpi you will see that photoshop would re-calculate the NEW size based on the amount of dots in the picture. In this case it would be approx 8-10 inches at 300 DPI.

For the web 72 dpi is fine but WITHIN the size of 8-10 inches. HOWEVER to PRINT that on a commercial press you would need the file to be at the final size (if its a flyer at 8.5"x11" for example) at least 300 DPI. In other words you cannot take that web image you got from Google (lets say) and try to make a magazine ad out of it, the dpi would be too low and teh size too small. If you tried to increase it it would look blurry and icky. (try in Photoshop and you will see)

72 good for web
72 (at actual size or bigger) bad for commercial printing.

OK. THAT wasn't so simple. . . Sorry!

"Try not, Do! or do not, there is no try."
-Yoda

i can't answer that

Submitted by gwells on Thu, 2008-07-03 22:21.

i can't answer that question. you'll have to see if when you change the DPI with resampling turned off leaves you with a large enough image for what you need.

Make sure when you change

Submitted by natobasso on Fri, 2008-07-04 03:07.

Make sure when you change the res up to 300 that the image size (in pixels or inches of length and width) goes down proportionally. That way the ratio is 1:1 as gwells and ivan have stated.

You can scale up an image in steps to make it larger, but you gradually lose resolution/sharpness. The computer "interpolates" pixels that don't exist and that's why the blurriness occurs. As long as the image you are using is clear at 300dpi, is at 100% in your layout you should be fine.

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