How to set vector/raster to "centimeter" into bigger canvas?

[cadudesun]

Hi,

I created a canvas with 10 x 15 cm.

I am unable to create a vector rectangle or to set a raster image layer to fit 3 x 4 cm. I intend to fill the 10 x 15 cm canvas with a plenty of 3 x 4 cm photos.

a) Considering a rectangle vector, I set it to 300 x 400 (width x height), but the size don't match 3 x 4 cm, since the ruler (preferences/units/ruler) is set to cm an it is clear the 300 x 400 vector is smaller than 3 x 4 cm. Then, how could I set vector size to millimeters or centimeters?

b) I paste an image as new layer in the 10 x 15 cm canvas. The pick tool allows just scale the image, but I would like to obtain more control over raster image size. So, similarly to the vector issue, how could I set raster size (layer image into bigger 10 x 15 cm canvas) to fit 3 x 4 cm exactly?

Thanks in advance,
Cadu

[LeviFiction]

Do the math.

Technically for images you can just resize them prior to copying and pasting them. That should make it simple but for the sake using the pick tool or drawing vectors to size you need to know how many pixels there are per cm.

So what is the resolution of your image? If you don't know you can go to Image->Image Information on the menu bar or just hit Shift + I.

There it will show either Pixels Per Cm. Or Pixels Per Inch.

So, for example I know that there are 118.110 pixels per cm in a 300 pixel per inch image. So to get an image that is 3x4cm I just have to do the math by multiplying my number of inches times the number of pixels per inch.

The result is: 354x472 in pixels. (Rounded down on each because they didn't quite reach ".5")

This will of course be different based on your image's resolution.

[cadudesun]

Thanks for explanation LeviFiction!
PSP is complicated when dealing with resize objects in general. It would be simpler if be possible to choose the measurement of interest.
I did a workaround by setting the ruler to "centimeter" and then resize the objects (using pick tool) based on the ruler measure.
Bye,
Cadu

[dwalby2]

The problem becomes simpler when you ignore the centimeter or inch designations temporarily and work only with pixels, because that's what you're really doing anyway.

You can print 10x15cm with an image that's 100x150 pixels, and get a print density of 10 pixels/cm, or you can print 10x15cm with an image that's 1000x1500 at 100 pixels/cm. Either way you get a 10x15cm print, but the images you print from are completely different sizes. Decent print quality is generally around 250 pixels/inch or about 100 pixels/cm, so use that as a guide.

So if you want 10x15cm @100 pixels/cm, create a blank new image with the dimensions of 1000x1500 pixels. Now, say you want to put 4 smaller photos into that box, each one would be 500x750 pixels. Then take each of the 4 photos, crop/resize to 500x750 pixels and paste into the blank image as a layer. Make sure you select the layer with the desired small image, then you can drag it to the position you want in the larger image. Do this 4 times and you now have your composite 1000x1500 pixel image, merge all the layers when you're done positioning things. Now, you can print 10x15cm @100 pixels/cm, or you can resize the large image to any pixel size you want. Make it 2000x3000 and print at 200 pixels/cm, its up to you. the program just uses some default pixel/cm or pixel/inch designation, you don't have to follow that, you can make it any value you want by resizing.

When working with images for print, its generally better to start with more pixels and resize downward (rather than upward) to your final print size, or just print with more pixels/cm rather than 100. You may not actually see a difference in print quality, but it doesn't hurt either. With the high MP count of just about any camera today its easy to have a very high number of pixels/cm in your final print. So in the previous example you could have started with a blank image of 2000x3000 pixels or even 3000x4500 instead of 1000x1500.

[cadudesun]

Hi dwalby2,
Thanks for more explanation!
Best,
Cadu