Making images with 300 dpi

[rich2005]

Your book 8" x 10"  @ 300 ppi = 2400 x 3000 pix  How much for margins ? say 0.5 " all round gives a working size 7" x 9" @ 300 ppi = 2100 x 2700 pix.

So you would make your canvas (a template)  in Gimp 2400 x 3000 with a resolution of 300 ppi. Put in some guides for margins/bleeds. Anything you add to that  takes the 300 ppi setting.

So set the export in LibreCAD  to something that fits in 2100 x 2700 **Look* at the screenshot in post #3 **Change** the size.
jpeg is a poor format for export your smaller image as a png is not a monster file size.

Import the file made by LibreCAD File -> Open as layers  Even if you need to a little scaling to fit, the base image is 300 ppi and that is what you will get when you finally come to export.

The 96 ppi output from LibreCAD is common for vector appications, Inkscape is the same. A vector can scale up or down without quality loss **until** you render it to a bitmap.

Edit:

Here is an example: https://youtu.be/xW3f9yMadHE  2' 30'' - no audio

[snowforest]

Thanks nice video but aat 1:50 it is extremely fast and I don't understand what is going on. You click image and then what?

I have 300+ images and although applying your procedure obviously is great, it will take me very long and cause to make mistakes.

Can I just do this: Export with 96 dpi from librecad and just open that image in gimp and go to print size and adjust dpi in gimp and that's it? I will then resize to whatever size I want, most pictures will be smaller than the whole page width and height minus margins. And so far and from my looong time habit I was doing all jpg but from now I will do png per your recommendation.

And one more thing, I just tried to export as png, and there are lot of check boxes,, the first 4 seems related to web right? So they dont need to be checked? and then save comment and save color values from transparent pixels also were unchecked, so I should just leave them unchecked? The only thing I will check extra is the save IPTC data although I didnt put in anything special for it but still....

[rich2005]

Quote:Thanks nice video but aat 1:50 it is extremely fast and I don't understand what is going on. You click image and then what?

At that point, I have opened the png I got from LibreCAD as a layer over my page template. Not quite the correct size to fit between the margins so I use the scale tool to make it a better fit. Not the sort of scaling you have to do, 9000 pix > down to 900 pix more like 2100 pix down to 2000 pix Not much in the way of reduction in quality.
The other thing to note, right at the end, The template was set up @ 300 ppi so anything I put in that template takes that value. (obviously).

Quote:I have 300+ images and although applying your procedure obviously is great, it will take me very long and cause to make mistakes.

Please, what is so difficult with setting that image size. LibreCAD (same as other vector applications Inkscape / CorelDraw typically use 90 or 96 ppi) Only the image size in pixels matters in Gimp.

However. Do not worry. It happens all the time, especially with book authors, but usually the other way round.
Open Gimp, make a page 8" x 10" but never check the ppi and get a default 96 ( or 72) ppi . Make their project and then find it is dreadful quality because everything has to be scaled up x3. You are the reverse big images to scale down to fit.

Quote:Can I just do this: Export with 96 dpi from Librecad and just open that image in gimp and go to print size and adjust dpi in gimp and that's it?

No, not in this case. That is a setting that the printer uses.
In Gimp you need the image the correct pixel size to fit your page template. I hope your page template is set up at 300 ppi and not 96 ppi. The size should be round about 2400 pix (8") x 3000 (10") for your project. You need your LibreCAD exports about that size.

Since you have already converted your 300+ LibreCAD drawings without changing the jpeg output image size in the LibreCAD export you are now stuck with a lot of drawings that you will have to scale down to fit your page template. Not going to be wonderful quality.

[snowforest]

Ok but after doing the way I suggested and saving and closing, when I check the image properties on windows, outside gimp, by right clicking on the image file name, I see that its dpi is now 300, which was my goal, so why does the method I suggest not work (either when I did it with scale or print size and both work) . I even opened the image now with irfan view for instance and saw that indeed its dpi is 300 , which was my goal. And resizing the image is ok, i can even do it easilly with MS picture viewer. After I obtain the 300 dpi image I just make it smaller with MS picture viewer etc... and thats it.

[rich2005]

As long as you are happy with the result, that is all that matters. Hopefully you have learned a little how LibreCAD and Gimp works.

[snowforest]

(07-28-2021, 12:36 PM)rich2005 Wrote: As long as you are happy with the result, that is all that matters. Hopefully you have learned a little how LibreCAD and Gimp works.

Yes thanks, it was informative and I will refer back to this post land your video later too and I am sure it is informative for others as well. For now, even the size I export from librecad doesnt matter. I simply convert it to 300 dpi first, and then make it smaller, and thats all. I usually make it even smaller when I insert to the book, according to the page layout so the final size is determined inside the book page after I insert the image, which is still smaller than the final size I made, not to loose quaity. So yes always some size is wasted as file size but that is within tolerances. Thanks for the answers.