# HELP!!  Finding correct trimming ratio on photographs - Photoshop



## gatorcruz (Jul 10, 2009)

Hello,

I use Photoshop CS3.  My original files are PSD files in 9000x6000, 300dpi, 20x30" files that I "save as" JPGs for photo processors (MPix, MyPhotopipe, for instance)

I want to print these files in their current ratio (3:2) on 20x30, 16x20 and 12x16 sheets which will result in having a white, unprinted, trim as follows:

(A) 20x30 sheet with a 18x27 centered image
(B) 16x20 sheet with a 12x18 centered image
(C) 12x16 sheet with a 10x15 centered image

OK, here is my problem.  I cannot figure out the formula / ratio where I can ADD, with the "Canvas Size" tool, a white trim around the existing 20x30 PSD file without having to resize the image.  For example, what CANVAS SIZE would I have to add to a file that is already 20x30 which will result in an image that is a perfect fit into the "(B)" sheet?  (Same question for the 12x16 and the 20x30 sheets (A) and (C).)

I am sure i am doing a poor job describing my question.  So, let's use (B) as an example.  Ordinarily, I would take my 20x30 PSD file and resize the image to 12x18 then ADD a 16x20 white background canvas to the image.  However, I feel that this reduces the quality of the image (because I reduced the size).  So, how can I keep my original 20x30 file?  What canvas size would i have to make to come up with the (B) description?  How did you go about this?  What simple formula did you use?  I am sure, once i get it, i could apply the same technique to every ratio.

well, thank you for your help.


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## Josh66 (Jul 10, 2009)

gatorcruz said:


> Ordinarily, I would take my 20x30 PSD file and resize the image to 12x18 then ADD a 16x20 white background canvas to the image.  However, I feel that this reduces the quality of the image (because I reduced the size).



That's how I would do it.

Quality shouldn't suffer.  You didn't reduce the image, you just made the canvas bigger.

Oops...  Just re-read your post.  Don't resize.  As long as it's the right aspect ration, size doesn't matter (as long as it isn't too small).


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## KmH (Jul 10, 2009)

I don't know about the others but Mpix always centers the image so you don't have to add canvas. The image just won't fill a 20x30 sheet as long as you size it to 18x27. Same with the other sizes.

Here is a link to part of Mpix's support pages

However, make a white canvas the size you need say 20x30 and the same resolution as your print. In your case it looks like 300 ppi (by the way dpi is something very different).

Once you have the canvas pull vertical and horizontal guides from the rulers and put them at 1" and 19" and 1.5" and 28.5" respectively.

Under the 'View' tab click on 'Snap to'. Drag the image onto the 20x30 canvas till it 'snaps to' the guide lines.

Save it.


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## gatorcruz (Jul 10, 2009)

Hello KMH,

I appreciate your reply but I don;t think it will work.  In repky to your comments:

(MPIX) Mpix automatically centers images but will not fit my needs.  For example, if my file is 20x30 and i want to keep it 20x30, then MPIX will automatically accept the file as a full bleed on a 20x30 print (unlike the 20x30 print with an 18x27 image centered).  The same file would be automatically fit into a 16x20 image with a 13.333"x20" image (no trim on the top and bottom and about a 1.33" trim on the other two sides ... varying greatly from my discribed needs.

(PPI) Woops, sorry .. yea, I meant PPI, not dpi

(Snap to guides) Unless if i am not understanding the function, this will also not work because it will alter the size of my original 20"x30" PSD files.  Once again, I would do NOT want to reduce the size of my original files.  i rather add the appropriate canvas size onto the 20x30 file which will result in a perfect ratio that will meet my aforementioned ratios (A, B and C).  

With your example, for B, I would create a 16x20 Canvas, set the guides with a centered 12x18 then SNAP drag my 20x30 image into the 16x20 canvas which will essentially result in a REDUCED resizing of my image (what i wanted to avoid).  i would get the same results by just reducing the size of my 20x30 300ppi image to 12x18 300ppi then adding a white 16x20 canvas.

but, thank you for the ideas and perhaps my reply better describes what i am looking to do ... Any new ideas / solutions?

Thank you



KmH said:


> I don't know about the others but Mpix always centers the image so you don't have to add canvas. The image just won't fill a 20x30 sheet as long as you size it to 18x27. Same with the other sizes.
> 
> Here is a link to part of Mpix's support pages
> 
> ...


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## KmH (Jul 10, 2009)

You're right, your description didn't work for me.

From rereading your desciption what you are trying to do can't be done the way you are tying to do it because of a difference in aspect ratios. Sorry.

At best, you must add more canvas than you need and crop to the desired, final canvas size.

Regardless of what you believe/feel, reducing the size of your file does not diminsh the image quality if the proper algorithm is used to effect the reduction and 300 ppi is maintained.

I hope you figure it out.


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## Dwig (Jul 10, 2009)

In Photoshop its simple; no math required:

1. Access Image/Image Size...
2. Uncheck "Resample"
3. Change the size to desired image size (e.g. 12x18")
4. Access Image/Canvas Size...
5. Change the canvas size to 16x20.

No pixels were harmed in the making of this movie...er...resizing this image!

With "Resample" turned off, all PS will do is change the PPI in the image header. The new PPI will result in the image being a different size in inches. When you do the Resize, your 6000x9000 pixel 20"x30"x300ppi image will become a 6000x9000 pixel 12"x18"x500ppi image. The actual image pixels are not touched in the process; only the EXIF data in the image header is altered.

Whether there is any value in doing it this way is questionable. Downsampling the image so that it is a 12x18x300ppi image will almost certainly result in the same image detail being visible on the actual print. Five years ago or so, printer drivers and RIPs weren't as elegant and printing an image with an odd increment PPI value (not a interger multiple of 300ppi) could sometimes result in lower quality than a lower PPI value that was as multiple of 300.


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