ppi and image size

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Another of those great questions...:bang:

can anyone tell me what size image and ppi I need if I wanted to produce a jpeg file that is use for A4 sized print (brochure) with 300ppi

I was thinking exporting out of Lightroom as a file with long edge 297mm with 300ppi as the settings? Is this correct or have I been having too many late nights and early starts......:thinking:
 
As you are measuring your resolution in inches (300ppi) just multiply the size of your output document (in inches) by 300. This will give you the size of the image needed to meet your requirements.
 
If it's being used as a full page in an A4 brochure then the size would be: 303mm - as there is usually 1.5mm bleed all round!

Tell us the size of your file out of camera? That would help.
 
thanks for the info.

well I think I might recommend not using a full size a4 spread then... as I realised I've been shooting in SRAW from a previous time..... :head smash into wall smiley:

the file size comes up as 2.MP
 
is that the file size - or the image size - not the same thing in jpeg!
 
what... I look at teh actual DNG converted file from lightroom on the hard drive and the file size there is around 6.8meg

in LR I can display megapixel in the loupe (description view) and thats 2.5MP

the actual cropped dimension is 1217x1825

Now I'm confused a bit!

Shed any light? please?
 
at 300dpi that image would print to 6" x 4" - divide pixels by 300
 
Starting from the start!

ppi stands for pixels per inch. You can calculate the resolution of a printed picture by dividing the number of pixels across by the width of the picture (or by dividing the number of pixels down by the height of the picture)

Any picture that you have will be a certain number of pixels across and a certain number of pixels down. For example a picture could be 3000 pixels by 2100 pixels.

When you print the picture it will have a certain physical size, for example 10 inches by 7 inches.

Therefore that printed picture will have 300 pixels in every inch across and in every inch down, i.e. it has a resolution of 300ppi. (3000pixels across divided by 10 inches across, or 2100 pixels down divided by 7 inches down)

You can also use choose the resolution figure and, using the pixel size, calculate what size print you will get.

You say that your print is 1217 pixels by 1825 pixels.
If you choose a resolution of 300ppi your print will be about 4 inches by about 6 inches (1217/300=4.056, 1825/300=6.08 both approx).

If you want your print, which is 1217 pixels by 1825 pixels, to be A4 (approx 8.26 inches by 11.7 inches) you need to print at a resolution of around 155ppi. this will give you a print size of 7.85 inches by 11.8 inches.

If you want to print at a higher resolution you will need to resample, i.e. add pixels to your image using your editing program - this may, or may not, give an acceptable result.
 
Your way of exporting from Lightroom would work, providing you allow Lightroom up upscale the image. The quality won't be quite as good as upscaling with specialist upscaling software such as Genuie Fractals, but it will be the size and resolution you need.
 
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