Exporting from lightroom to meet a requirement

tzalman wrote in post #17869381
As I noted above, the amount of compression applied to the jpg and its resulting size have no affect on the uncompressed size; all you need to know is the total number of pixels (height x width). Multiply that by 3 for a rough estimate. 2.86 to be more accurate.

For instance: 4000 x 6000 pixels = 24MP x 3 = 72MB

sorry i think i missed that - that's great & very useful

Yes look at EITHER my first posting directly above the one by Elie, OR the post by Elie, directly below mine, where we both explain exactly the same thing. Pixels times three, to give you uncompressed file size in bytes or Mega Pixels ×2.86 for file size in Mega Bytes. Either of those is always true and is all you need to know.

It can't be much easier really.

Alan

If you need to resize a moderate amount to fall in the 17.5 - 25 MP window, LR will do it at least as well as any other application, maybe better than most.

No, leaving the Resize box in LR unchecked will give you the native size of your image (as it came from the camera) minus any cropped sections or changes caused by lens or perspective corrections or straightening. I.e., "the largest possible" image without additional resampling being done.

tzalman wrote in post #17869401
If you need to resize a moderate amount to fall in the 17.5 - 25 MP window, LR will do it at least as well as any other application, maybe better than most.

No, leaving the Resize box in LR unchecked will give you the native size of your image (as it came from the camera) minus any cropped sections or changes caused by lens or perspective corrections or straightening. I.e., "the largest possible" image without additional resampling being done.

im not familiar with doing this in LR (never used it)

if i go to export, then image sizing, then resize to fit? is this the right place?

ive then got a number of options - which one(s) am i best using? most of the tutorials seem to focus on the dimensions & edges

wellsie82 wrote in post #17870420
im not familiar with doing this in LR (never used it)

if i go to export, then image sizing, then resize to fit? is this the right place?

ive then got a number of options - which one(s) am i best using? most of the tutorials seem to focus on the dimensions & edges

looks like ive sussed it

image sizing > tick resize to fit > width & height > w: 5500 > H: 5500 > pixels > 300ppi

the width & height tab was previously making me think that having the two fields the same would give me a square image but having dug around on some more blogs/tutorials this is the longest side only

clearly the more i crop, the less this will work, but as a guestimate, is 5500 pixels on the longest side ok? i mean, it seems to do the job in terms of the image size but would it impact IQ being that large a number? the default was 1000 in both fields

wellsie82 wrote in post #17870420
im not familiar with doing this in LR (never used it)

if i go to export, then image sizing, then resize to fit? is this the right place?

Yes.

I don't think it makes a lot of difference, because (unlike PS) LR will never change the aspect ratio of the image. If you start with a 5D2 image that is 3744x5616 pixels (21 MP - great for the agency at that size) and you have to crop it to 3300x4950 (still 2:3), which is 16.3 MP and below the minimum, so you want to upsize it to 18 MP which is 3464x5196. You could write in those pixel dimensions or just one of them for long side or short side and since LR won't change the ratio the other side will come out right. But that is hard work; to find the appropriate dimensions for 18 MP I had to figure out the square root of 3 million. And if it hadn't been in the 2:3 ratio after the crop but rather some more complex ratio it would have been even harder. LR makes it easy with the Megapixels option - just type in 18.

The minimum is around 17.5 MP, so if you fall below that I would go for 18 MP or 5200 pixels long side. I think an increase of 25%, say 4200 to 5200 would have no discernible effect on quality.

Here is an example of how well LR can do at resizing. I have used these images as examples previously, but not in this specific context.

Here is an image that I wanted printing at 30"×20", and the pro lab service that I use requires you to resize the image to meet 300 PPI, which for that print size is 9000×6000 pixels or 54 MP. Here is the original full image resized to meet the POTN posting limits.

Photo from BigAl007's gallery.
Image hosted by forum (760438)

Photo from BigAl007's gallery.
Image hosted by forum (769126)

Photo from BigAl007's gallery.
Image hosted by forum (769127)

tzamlan & bigal2007 - this is great insight & your replies were very useful

seems ive learnt something in LR today which i never knew existed (not that id needed it beforehand)

many thanks everyone, appreciate all your input in helping me out here