How to prepare image to certain size print?

I need to print photo in 15x21 size and matt it to a4 size paper. Any advice on how to do this? This is my first time matting a photo.

I may not be understanding this:

If the image size is A4 roughly 8.5x11" than printing it at 15x21" isn't possible.

Is the final mounting size for the frame supposed to be 15x21"? The framer will cut a window relative to the expected display framing so all you need to do is print the A4 size. The picture will be mounted to a backing then that and the mat board mated together. Common mat when cut have a bevel that extends about 1/16"-1/8".

1. image printed to 15" x 21" (which does not make sense) or 15cm x 21cm?
   
2. print on A4 (210 x 297 mm)
   

I made a quick line drawing to help clarify what you are describing - hopefully I interpreted your description correctly.

When you go shopping for pre-made frames, they often list the frame size and then the included mat opening size (see attached photo of an example frame). The mat opening is usually sized for a common aspect ratio and paper size. An A4 mat opening will probably be slightly smaller than an A4 piece of paper.

I actually happen to have a 15x21 frame lying around! In the attached photo of the frame, the mat opening is for an "image" (paper size) that is 11x17 inches, but the mat opening is ~10.5 x 16.5 inches when you actually measure it. That is, the piece of paper that you would probably choose to print the image for this frame is an 11x17 paper. This gives you about 1/4" margin around the paper edge to mount the image centered in the mat opening.

In my frame example, I would configure and crop the image to print at about 10.75 x 16.75 on the 11x17 paper. This will cause the very edges of the image to be masked by the mat, but will insure that there is no white paper showing at the edge of the mat and pretty much the entire image will displayed in the mat opening. Then I would center the print in the mat opening and install it in the frame.

Kirk

Thanks for helping guys. I was a bit unclear.. sorry about that. This is for school project and I have prepared 8 photos in 15x21cm size. This is how brief goes.
''Photographs must be presented using the matting technique - the archival standard for photographic prints. The mat should be in the form of hard white paper at least 300g in weight. For a photographic print of 15x21, the matt size should be the same as an A4 piece of paper,,.
It is supposed to look like this (not my print)

1. You can print your image to be just a bit larger than the dimensions of the opening (or you can print your image to leave a white border surrounding the image)
   
2. You place the correct sized mat (considering both dimensions of frame to be mounted and dimensions of the image to be matted) into be centered about the image area of the underlying print
   
3. You secure #1 to #2, using acid-free mounting media for mounting photographs (usually ordinary tape is not great, if you value longevity of mounting...adhesive failure to hold, maybe adhesive staining print or mat)
   

I'd also make the print with, say, a 65mm white border such that while the overall print size is 15cm x 21cm the image area would be 13.7cm x 19.7cm. Then cut a 13.7cm x 19.7cm hole in the A4 sized mat and follow Wilt's instructions for putting it all together.

Thanks for claryfing. So the opening should be self made? would it be a problem if image is exact size as opening?

kundurovic wrote in post #19404715
Thanks for claryfing. So the opening should be self made? would it be a problem if image is exact size as opening?

It will work either way, being a matter of artistic taste. I cut my own and prefer to have an exact size opening but have done it the other way with very nice results.

LOL - looks like I was 100% incorrect! Thanks for clarification.

Consider using a mat cutter and not just a utility knife. The resulting opening will (if you choose) be cut with a bevel and the cutter permits controlled, clean plunge cuts at the internal corners of the opening.

good luck!

Kirk

Mat cutters are not inexpensive...for a school project it may be less expensive to simply buy precut mats from framing shops. But for long range planning, an investment today in a mat cutter can ultimately prove to be a savings.

A mat cutter can be only about $35, but you need a suitable surface to use it, and to have a nice metal straight edge to guide the mat cutter in a straight line...leading to mat cutters that have integral straight edge that costs $150-500!
So you see you need a certain volume of mat cutting for it to be a sensible purchase...in my 60 years in photography, I never purchased a mat cutter, preferring to simply go to a frame shop and specific custom cut mat color and size.

For decades - especially when I was back in college - I never had a proper mat cutter. I used a metal ruler, poor box cutter knife and a poor surface; ruined a lot of expensive board.

When I went digital back in 2006 I finally bought a proper mat cutter by Logan. They are very high quality and have a number of sizes and prices to fit your needs. It was the best money I ever invested. Blicks or Dick Blick art supplies periodically has coupons and I got an expensive cutter for 1/3 off. I do a lot of exhibition work so it saved me a ton of money. We won't talk about the amount though I've spent on mat board

If you'd like to see how I cut my mats, here's an old thread from some years back; wish I still had that hair

https://photography-on-the.net/forum/showthre​ad.php?t=459308

Stu

kundurovic wrote in post #19404715
Thanks for claryfing. So the opening should be self made? would it be a problem if image is exact size as opening?

The overall paper dimensions of the print have to be a bit bigger than the hole in the mat. Since you usually don’t want to cut off parts of the image when you mat it you print the image with a border.

You can print with an even wider border than what I suggested if you like (e.g. a 31mm border) which works nice if you were using a coloured mat such that you’d have 16.5mm under the mat and 16.5mm white border showing.

For white mats I like the border to be behind the mat so only the image area shows.

Does your instructor specify the mat must have a window cut? In my day we mounted them simply to the backing board and submitted them for the project. We'd print the image full bleed or leave a boarder. Back then we bought pre-sized 11x14" mats, window cuts were not necessary for our projects. (Would add to the cost so this helped us save some $ in that regard.)

A good mat cutter makes life nice but they can be expensive. Learning to accurately place the window cut is useful to learn.