Master and Version sizes

Question

Can someone please explain file sizes as they relate to Masters and Versions? I still get confused about this point. I would think my Master image would contain the most data, and therefore have the larger file size than its versions. However, perhaps I am mistaken on this point. When I export Masters, the file sizes are always a lot smaller than the associated versions that I export.
When I export a version, I am exporting it at JPEG Original size, so isn't this compressing the master? I thought this would cause it to have less data? I'm just really unclear about why the sizes differ and what is going on. For example, my Master JPEG might be 2MB, but an exported version of that image could be something like 4.46MB.
Mac

Answer 1

macorin wrote:
Corky,
Thanks, great stuff!
I have a few follow up questions. I hope it doesn't get too confusing.
1. The camera takes a picture. When I see an image size in Aperture of 2 MB, is that the same size that the image file was when the camera took it? Then it compresses it into a JPEG even if I was shooting in JPEG instead of RAW? So the 2 MB size image gets compressed to say 1 MB and then upon import into Aperture it gets uncompressed again and is seen at 2 MB?
With Aperture, the reported size of the file in the Metadata Inspector pane is about the size on disk (slightly smaller in my experience, but close). I am not sure what Aperture is doing here, but you can think of it as the space used on disk by the Master file. Aperture is not reporting the un-compressed (expanded) file state as Photoshop does when you work on the same file.
In the case of a digital camera, you capture an image and the sensor in the camera records the brightness value of the scene on the 'photo sites' of the sensor (the amount of photo sites on the sensor is expressed in Mega Pixels (means million pixels) by multiplying the number of sites in width by the number of sites in height). In this instance, Photo Site is expressed as pixel (3200 pixels x 2400 pixels = 7,680,000 pixels - or 7.68 Mega Pixels). The light captured by the camera travels through a color filter matrix where each site has a color value assigned to it.
When you shoot JPEG, the camera takes the brightness data from the sensor, combined with the color data collected and applies what is called a 'demosaic' process which predicts what color each adjacent pixel is to create a color image with smooth transitions between colors. The camera then processes this data (and applies compression in camera) to create a JPEG. This process does throw out data the camera software (firmware) decides is unnecessary to create a final JPEG image.
Current digital cameras do a good job (for the most part) of processing a nice JPEG image. If you shoot RAW, you are telling the camera not to process the sensor data and to save the uncompressed data for you to do the processing via a RAW processing program such as Aperture.
In short, the 2 MB file size you see in Aperture is what your camera delivered to the camera card after processing (although it might be 2.3 MB or something on disk).
2. If my scenario in #1 is correct, I still don't understand why a version being exported at a level 12 quality (which is where I set it) comes out roughly twice this size. Obviously I am missing something here. I understand about it being compressed less upon export if the quality setting is at 12, but it is still getting compressed, so how does it become bigger than the original size to begin with. Again, I am missing something there, so a little deeper insight would be helpful.
Based on my answer to #1, your Master file is 2 MB on disk and Aperture is reporting that to you. It is not telling you what size the uncompressed file size is prior to applying any adjustments and then re-compressing.
3. I do set my export quality settings to 12 as I want the highest quality file to be sent to photo processing sites for printing purposes. A) is this necessary and meaningful to get the best quality prints? B) Do I need to change the DPI settings to something higher than the default 72 when I export these versions for printing? I was always under the impression that 72 DPI was standard for viewing images on a computer screen, but not ideal for printing. Is it beneficial to change the DPI to something higher - 300 for example - for the purpose of exporting images to be printed?
For printing, you will want to export at 150 - 300 DPI. I have read many articles and some books which talk to this and most say that 240 DPI is as good as 300 DPI for all but fine art printing on high end machines. I typically use 150 DPI to start and see what the print looks like. There is no magic number for printing, it really is about verifying the result once printed and then you will know what setting you like the best.
One thing is that the higher the DPI you use, the smaller the size of the print at the native (original) resolution of your image. So for a 3200 x 2400 pixel image, you would exchange pixels for dots (in Dots Per Inch) which is used by the printer to put ink on paper.
3200/300 = 10.66 inches wide x 2400/300 = 8 inches tall
3200/150 = 21.33 inches wide x 2400/150 = 16 inches tall
In the examples above, you could print the same image at 10.66 x 8 inches or 21.33 x 16 inches depending on which DPI setting you export to print with.
4. I export versions and not masters when I am printing images. I do this because I generally make all of my edits in Aperture and I want those versions to be printed. It still seems odd to me that exporting versions gives me a larger file size than when I export masters. Don't the masters get exported with the same quality settings - i.e. 12 - upon export?
Exporting the versions is expected because that is when any adjustments are 'baked in' to your final file outside Aperture.
Exporting the Master is basically copying the original imported image file out of Aperture. There is an option to write IPTC information to the Master on export, but - to the best of my knowledge - that does not require any uncompress / re-compress process.
Aperture only reads the data in the Master once to generate an image on screen for you to work with (at least this is my understanding). It's the version that is subject to any re-compression on export, not the Master. In this way, Aperture protects the original Master file from destructive alteration.
Anyway, those are my understandings. There are many here who are way beyond my skill / knowledge level, so hopefully I have expressed the information accurately and adequately.