Keeping the same Pixels Per Inch the same and varying the JPG quality knob definitely changes file size from (3,519KB at 100%) to (453KB at 61%).
Modifying the Pixels Per Inch 9and keeping the JPG quality slider constant at 100%), on the other hand does not seem to affect file size as I would expect it should 240PPI results in the same file size (3,519KB) as 120PPI or 10 PPI for that matter.
Is this a bug in Lightroom? Or is there another way to export pics?
thanks
-Ed
PPI setting in export has no affect on...
PPI doesn't affect file size, be it i pixel per inch or 3000 per inch; it's the same number of pixels, the same number of bytes to conatin them.
PPI setting in export has no affect on...
Yes, you select the constrain size which is pixel dimensions.
PPI resolution is simply a data entry in the resulting JPEG file; it doesn't affect file size. An image that is X by Y pixels will be compressed to a given data size that depends on quality, and the conversion factor for px to in is simply added as a field.
Yayks. My whole world just flipped. I thought if you had a 4''x4'' picture at 240PPI, you had 4x4x240 pixels... but if you saved it as 120PPI, the picture would still be 4''x4'' but would only contain half the number of pixels per inch and would therefore look more pixelated (aliased). If this is not the case, that is the affect of changing the PPI when saving the file?
Thanks... my head is ready to learn this :)
-Ed.
As previous posters said: PPI value doesn't affect image/file or it's quality/size in any way -it's just info value.
So, what purpose does PPI value serve then? Where and when can you use PPI value (if at all)?
Suppose you created/saved jpg image which has resolution of 1800x1200 pixels at 300PPI. What size does this image have? Well, if you print it at 300PPI, then it will be 1800/300 x 1200/300 = 6x4'' (15x10cm). But you can print the same image at 150PPI (doesn't matter if you defined 300PPI when creating file). In this case you'll get image size of 12x8''. That is, you define PPI when printing.
As everything above 240PPI is considered as ''photo quality'', you could always use 300PPI when creating image file. On the other side, if really nobody cares about that value, is it OK if you always use value, for example, of 10PPI? Yes and no.
Assume you send a image to someone for commercial printing. In such case you can't know: what software they're using for printing and how big prints they may need. What would you do?
You send them image which has (for example) 3060x2040 pixels and 180PPI. What would that tell? That would tell, that image can be printed up to 3060/180 x 2040/180 = 17x11'' and still retain quality you see as acceptable -they would know, that image's content isn't ment to be printed bigger than that.
Usually process goes opposite way: when you wish to print, you usually define papersize first and software tells you then at which PPI image will be printed. Going further: when you print ''photo'' quality, it will allways be printed at some fixed PPI (300, for example) -if source image doesn't fit on paper, then it will be automatically resized to match predefined PPI.
Bogdan
%26lt;blockquote%26gt;%26lt;span style=''font-size: 90%%26gt;%26lt;i%26gt; I thought if you had a 4''x4'' picture at 240PPI, you had 4x4x240 pixels%26lt;/i%26gt;%26lt;/span%26gt;%26lt;/blockquote%26gt;Trying to put this simple: You don't ''have a 4 x 4 inch image'' at 240 ppi. Instead you have a 960 x 960 pixel image which at 240 ppi will produce a 4 x 4 inch print. If you print the same image at 480 ppi you'll get a 2 x 2 inch print, printed at 120 ppi, you'll get a 8 x 8 inch print. The pixels always stay the same 960 x 960.%26lt;br /%26gt;%26lt;br /%26gt;Even simpler: Images stored on your computer are measured in pixels instead of inches. Only printed images are measured in inches.%26lt;br /%26gt;%26lt;br /%26gt;Alexander.%26lt;br%26gt;%26lt;span style=''font-size: 75%; color: #408080''%26gt;-- %26lt;br%26gt;Canon EOS 400D (aka. XTi) %26amp;bull; 20'' iMac Intel %26amp;bull; 12'' PowerBook G4 %26amp;bull; OS X 10.4 %26amp;bull; LR 1 %26amp;bull; PSE 4%26lt;/span%26gt;
Thanks all. This makes sense. I was under the assumption that the picture size was constant and therefore lowering the PPI would reduce the file size. As Dogdan says... these days, print size is determined first, and the PPI is then set to match.
This is different than Photoshop... in all previous version of PS, a lower PPI would produce a smaller file.
Anyway, it sounds like the Quality knob is my only lever for reducing file size for pics I want to keep but will never print 11x17's with.
Thanks again for the responses !
-Ed
%26gt; Anyway, it sounds like the Quality knob is my only lever for reducing file size for pics I want to keep but will never print 11x17's with.
No it's not. You can constrain the image size to whatever you want.
elandau wrote:
%26gt;This is different than Photoshop... in all previous version of PS,
%26gt;a lower PPI would produce a smaller file.
No, this is only half true because it depends on the ''resample image'' checkbox!
If resampling is active a change of the ppi setting is also changing the pixel dimensions but keeps the physical dimensions. If you deactivate the ''resample image'' checkbox a change of the ppi setting is changing the physical dimensions but keeps the pixel dimensions.
Chris
I'm totally confused.
I edit in LR and export to a file to print in Qimage. Qimage automatically sets the ppi at 600 ppi. I define the size of the print in Qimage.
What settings should I use in LR export assuming I want the best quality print?
Andy
Rosss-
This question is hotly debated from time to time, and you'll get answers all over the lot. I've come to believe that as long as you have a reasonable amount of ppi- and depending on the ultimate size- you're fine with sending it to the printer ca. 240, or 300, or 360, depending on the printer. If it's really big, say 2' x3' you can go well under 240. Of course, the nature of the image is also a factor at large sizes, as is noise and sharpening.
Why don't you try a side by side, with printing say an 8 x 10 in LR @ 300 ppi vs. sending the same to Qimage?
Rossss,
John above gave you good advice to tryout. I would just like to comment your ''confusion''.
Qimage is a good product (I don't use it, so I assume), but you should understand it... it is not necessary to use it all the time.
AFAIK Qimage is most usefull at (very) big enlargements. It uses his own resizing algorithms, where better results should be expected as from printer manufacturer's software (says developer). Qimage also tries to print directly at printer's ''native'' resolution, which is 600ppi for Canon and 720ppi for Epson. It is logical, that if image is too small to print it at 600ppi, it must be resized (internal by Qimage).
I've tried Qimage on A4 paper (12x8'') with normal sized image and I couldn't find any benefit of using Qimage -so I conclude: if there's benefit, then print size should be much bigger (or source image very small).
As allways.. if/where I'm wrong, other posters will correct me :-)
Bogdan
I have compared printing 4x6 between qimage and LR and I can't can't see a difference. I get good results both ways.
In defense of qimage, I find it easier and faster than LR when I am printing larger numbers of pictures. It automatically sets the printer settings and also has excellent sharpening.
andy
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