Files may be Exported to a variety of formats inclduing JPEG. Size is dependant upon the output size specified and the quality (compression) value used. Can a file be gerater than 24 MB? Absolutely. Should it?
The idea of specifying a number of megabytes for a JPG comes up often, and it never makes sense to me. The number of megabytes of a JPG has no meaning in relation to quality or number of pixels or any other measure you might want to use. On the other hand, the number of megapixels, or the number of pixels on a side, or the number of pixels height and width, are all meaningful measures, even with a JPG.
So, to clarify, if I have an image saved as an 8bit Tiff at 34.4 MB. Can I then save that as a JPEG at 24MB or over with LR 4?
This is hardly a reason to purchase Lightroom. Other software can do this as well. I assume you want to use Lightroom's other features as well.
The answer is probably YES, you might have to upsize the photo (in other words, increase the number of pixels, and this can result in some quality degradation) to get a 24MB JPG, and I think you are going to have to do this by trial and error, there is no algorithm in LR to produce a 24MB or larger JPG. So I say "probably YES", but I admit I have never tried to do this myself.
And as I said before, there is no good reason to specify a specific size for a JPG. This is a bizarre request, in my opinion.
Probably depends upon the Tiff. What is it a photo of? Different photos compress differently.
How many layers are in the Tiff? Or, is it pre-flattened when you measure the 34 MB. Many layered Tiffs compress more readily as they are flattened.
I would like to know Why? What is the driving force behind this since it is such a meaningless statistic about a file's quality/size/resolution?
Perhaps if you could tell us where the arbitrary 24 MB number comes from we could advise you better.
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