07-20-2018, 08:43 AM
Going back to the subject: "Get Photos Right Print Size - And All The Same!"
1. All The Same: Gimp works in pixels.
If you want the individual photos all the same size then you need to scale each photo individually to the same dimensions in pixels. It sounds like you are doing that in place on the canvas using the scale tool. I would pre-process each before starting using Image -> Scale Image Both get there in the end, but Scale Image is that little bit more predictable.
2. Right Print Size Printing is where pixel-per-inch (ppi) comes in. You can use any value for this, eye-of-the-beholder comes into play. Viewing the print at a distance (a poster) and a small value is ok, a 6"x4" photo and a larger ppi is needed. The convention for photographs is use 300 ppi. Larger is ok, some scanned images might use 600 - 1200 ppi but generally not much benefit using large values.
Gimp is not that clever, a pixel is a pixel, scale down and pixels are thrown away, scale up and pixels are guessed (interpolated) and added. Both actions degrade the image although you can get away with scaling down a little.
Worst case for your photos 737x1072 pix > 234x340 pix scaled down 3 times. That is why I recommend ditching your 180 ppi and go for a higher print resolution. The print shop will still print a 6"X 4" whatever the print resolution, it is only a setting in the image file.
What does happen: Copy & Paste, Import as Layers, drag-n-drop and the properties of the destination image are used. Your 6"x4" canvas @ 180 ppi (1080x720 pix) then that is used. Use 6"x4" @ 450 ppi (2700x1800 pix) that is used. Your individual photos do not change, a pixel is a pixel
180 ppi is unusual for a default. Used to be 72 ppi which is/was the pixel resolution for a computer monitor matching the requirements for web-pages. Look at the drop down list of standard templates. Lots @ 300 ppi for printing but the Web Banners still 72 ppi, while the phone templates high for those displays.
Using 72 ppi is one of the main reasons for disappointed beginners when their work is printed (think logo on tee-shirt)
Gimp 2.10 and the default canvas is now 300 ppi (1920x1080 pix)
You can see layers, a stack of images one on top of another. Some will hide anything underneath. Think of a mask as making a layer into a window, parts of the window are opaque, parts are transparent. You can see through the transparent bits to whatever is underneath.
Keep trying, you get there in the end.
1. All The Same: Gimp works in pixels.
If you want the individual photos all the same size then you need to scale each photo individually to the same dimensions in pixels. It sounds like you are doing that in place on the canvas using the scale tool. I would pre-process each before starting using Image -> Scale Image Both get there in the end, but Scale Image is that little bit more predictable.
2. Right Print Size Printing is where pixel-per-inch (ppi) comes in. You can use any value for this, eye-of-the-beholder comes into play. Viewing the print at a distance (a poster) and a small value is ok, a 6"x4" photo and a larger ppi is needed. The convention for photographs is use 300 ppi. Larger is ok, some scanned images might use 600 - 1200 ppi but generally not much benefit using large values.
Quote:GIMP is that clever ? It actually changes the pixels per inch? What's happening there? It must be throwing pixels away on some edits, creating new pixels on others?
Gimp is not that clever, a pixel is a pixel, scale down and pixels are thrown away, scale up and pixels are guessed (interpolated) and added. Both actions degrade the image although you can get away with scaling down a little.
Worst case for your photos 737x1072 pix > 234x340 pix scaled down 3 times. That is why I recommend ditching your 180 ppi and go for a higher print resolution. The print shop will still print a 6"X 4" whatever the print resolution, it is only a setting in the image file.
What does happen: Copy & Paste, Import as Layers, drag-n-drop and the properties of the destination image are used. Your 6"x4" canvas @ 180 ppi (1080x720 pix) then that is used. Use 6"x4" @ 450 ppi (2700x1800 pix) that is used. Your individual photos do not change, a pixel is a pixel
Quote:GIMP has decided 180 ppi I suppose because that's the default on my setup when I ask for a new canvas.
180 ppi is unusual for a default. Used to be 72 ppi which is/was the pixel resolution for a computer monitor matching the requirements for web-pages. Look at the drop down list of standard templates. Lots @ 300 ppi for printing but the Web Banners still 72 ppi, while the phone templates high for those displays.
Using 72 ppi is one of the main reasons for disappointed beginners when their work is printed (think logo on tee-shirt)
Gimp 2.10 and the default canvas is now 300 ppi (1920x1080 pix)
Quote:. I don't know the difference between a mask and a layer.
You can see layers, a stack of images one on top of another. Some will hide anything underneath. Think of a mask as making a layer into a window, parts of the window are opaque, parts are transparent. You can see through the transparent bits to whatever is underneath.
Quote:..I don't know what to do, if anything, about 'floating layers'..Typ. (Floating Selection)Pasted layer It is temporary. Treat as another layer and move, scale, rotate if required. When finished make it permanent, either anchor it, which merges into the active layer or make it into a new layer. Look in the Layers menu.
Keep trying, you get there in the end.