Making images with 300 dpi

[snowforest]

The images draw with librecad, when I export it as jpg, it only exports with 96 dpi. But I need 300 dpi. I turn it into 300 dpi using gimp. What do you suggest? Is gimp the best one to do it or another software or it doesnt matter? I use windows 10.

[Ofnuts]

The "DPI" is a somewhat meaning less metadata. The real measure is the size in pixels. See this for a start.

[rich2005]

When you export from LibreCAD it sets a canvas size in pixels depending on the drawing and the export resolution.
Change the setting to the size in pixels that you need in Gimp. This example the size changed to Gimp A4 @ 300 ppi 2480 x 3508 pix.

   

Then in Gimp use Image -> Print Size and change the 96 ppi to 300 ppi. This is an internal setting used by the printer and does not scale the image. The size in pixels remains the same.

   

[snowforest]

Ok but when i do from scale image still I do not need to change the image size. I can change only dpi from scale too. Is there a difference in terms of quality or other thing, between doing from print size or scale?

[rich2005]

Remember Gimp works in pixels. Did you read Ofnuts post on printing sizes ?

Quote:Is there a difference in terms of quality or other thing, between doing from print size or scale?

When you know the image size in pixels is correct but the ppi is maybe a default value retained from importing, then change the Print Size ppi value There is no loss in quality, it is an internal setting used by the printer.

Scaling up or down involves interpolation, some pixels are thrown away (scaling down) or pixels are guessed (scaling up) and this results in some loss in quality Might be a lot / might be small.

How this fits in with the scale dialogue. Remember again Gimp works in pixels. Keep your eye on the size in pixels

1) The original image, 1440 x 960 pixels imported resolution 96 ppi Gimp calculates that as 15" x 10"
2) I can scale that down to 12" x 8" The pixel size becomes 1152 x 768 and the 96 ppi I can leave alone if I want 12" x 8" print size.
3) If I want better print quality then I might increase the ppi to 300 The image size is still 1152 x 768 pix but now it will print with a size 3.84" x 2.56"

   

That is why you need to start off with a correct size in pixels Calculate Width (in inches) x 300 Height (in inches x 300) 
Do not start off with some size in inches or mm and a default ppi of 72 or 96 and find that you have to scale the image.

[snowforest]

I read ... so as far as I understand print size is better for dpi scaling, which I will do. What matters bottom line for me is that amazon wants 300 dpi images in the pdf I will send them. So I need to do it with print size then and scale will not work? I did a lot so far since this morning, I hope both works.... The images I will insert to the book need to be small in terms of the area they occupy anyway as I do not have much space available in pages as I am trying to keep the page count to minimum

[rich2005]

I do not think you fully understand. The ppi setting controls the size used by the printer. It does not scale anything.

Going back to the LibreCAD export. Make sure the size in pixels is correct so that scaling is not required. Then set the ppi to suit.

[snowforest]

from librecad the drawing size produced is far bigger than I need (thousand by thousand or more. I have at most 700 pixel wide space in my pages. But the jpg librecad exports is few thousand . So it is ok. I am just reducing the size of images to 700 pixel wide at most. But form my previous experience with amazon, if the dpi of a picture in pdf file was below 300, it gave error automatically and I remember going back and adjusting the dpi of those images to 300 and it had worked. That is my concern. Otherwise I am not also fond of adjusting ppi of a couple hundred images from 96 dpi to 300. . That is the only reason I am doing this. Are you saying I do not need to?

[rich2005]

Quote:Are you saying I do not need to?

From LibreCAD - I am saying that.
Go back and read post #3 , look at the screenshot Set the size in The LibreCAD export to the size in pixels you require. LibreCAD is vector. It will render any size you want to a raster image. No need to scale in Gimp.

What size is Amazon requiring for your publication.

[snowforest]

(07-27-2021, 01:49 PM)rich2005 Wrote:

Quote:Are you saying I do not need to?

From LibreCAD - I am saying that.
Go back and read post #3 , look at the screenshot Set the size in The LibreCAD export to the size in pixels you require. LibreCAD is vector. It will render any size you want to a raster image. No need to scale in Gimp.

What size is Amazon requiring for your publication.

Amazon doesnt require a particular size in pixel. It prints whatever we submit to them if it meets their quality quidelines. Now, my book is a 8x10 inch book. This means, on my pages after accounting for left and right margins, I have about 700 pixel or less available width for an image. So I can easily make jpg images from my drawings from librecad , to any pixel size I want, I know that part, but librecad exports them only as 96 ppi . I do not see a way in librecad to make them as 300 ppi. So I i export a certain pixel size of jpg from librecad, lets say a 2000 wide pixel image.

Then I must do two things.
1- Reduce it to 700 pixel wide at most (since it willl be a larger file if I didnt and would make my document unnecessarily larger file size, considering I have a lot of images)
2-I must make this image as 300 ppi since in the past amazon's system gave error for images below 300 ppi and when I adjusted those images ppi to 300, it had worked and their system removed error message for those images.