Posted by mark miller on September 14, 2010 at 2:57 PM
This is a new one for me. I scanned a bunch of slides, and sized them using PHotoShop CS4 to 10 by 15 inches at 300 dpi. All are in 8 bit, , and saved as jpeg optimum output of 12. No layers, of course.
Some of the jpeg file sizes are around 12 to 15 megabytes on some scans, which are about the same jpeg file sizes of equally dimensioned (ie 10x15 inhces at 300 dpi, 8 bit) digital files. Yet some others of the scanned images (all the same dimensions) have absolutely huge files, like 38 to 40 megabytes.
To give an example: one of my originals was a medium format. I scanned a pretty big file, as a tiff. Next I sized it to 11x14 inches at 300 dpi, 8bit depth. I saved it as a jpeg optimum out put of 12. In photoshop it is almost 40 megabytes as a jpeg, while outside of PhotoSHop in a folder, it is 30 megabytes. Another slide scanned will all the same above, is 40 megabytes in PhotoShop and about 14 megabytes in a folder, like the rest of the digitals.
I can't figure this out. I know that jpeg compressions are not all equal, but it seems they'd be closer than this. Wouldn't the final file size for equally dimentioned digital filesm whether scans from original slides, or digital originals, saved as jpegs all be somewhere about the same size megapixels?
Thanks for any feedback. MM
Posted by Buck Ward on September 14, 2010 at 5:51 PM
The amount of detail in an image can effect the JPEG file size. For example, an image with a lot of clear sky will produce a smaller JPEG file than an image with a lot of leafy forest detail. Of course, there may be other reasons for the disparate file sizes, too.
As a side note, I usually save my JPEG file at out put level 10 instead of 12. It gives smaller file sizes and I can't tell the difference. Of course, I saved the original master files as TIFFs.
Posted by David Bostedo on September 14, 2010 at 6:28 PM
Mark - Some of your statements are confusing - are you confusing megaPIXELs with megaBYTES? The two aren't necessarily related when you're talking about compressed file types like JPG. And what do you mean by the size in Photoshop versus the size in a folder? Are you again confusing megapixels with megabytes?
Posted by mark miller on September 14, 2010 at 11:30 PM
Yes, David, you're correct. I should have said megbytes consistently, as I just noted I called them megapixels also. IN a nutshell, some jpegs are around 30 megbytes in PhotoShop, and as saved in a folder, they are about 10 megabytes, which work great for file transfers. Yet, other jpegs in PhotoShop, as my scanned slides, start off around 40 megabytes will sometimes store in folders around 10 megabytes (like the digital captures) while others will will hardly compress at all. It may be as in response two, there's more detail, yet it seems to me, that some with equivalent detail, it appears, do compress well. A lot of this stuff with computers is just bizarre!
As far as lower quality compressing, or at least to 10, where it doesn't seem to show, I still prefer saving at 12 anyway, and that's because there may be times when an end user decides to interpolate, or also, in "save as" commands, if it is saved again, more info is lost. MM
Posted by David Bostedo on September 15, 2010 at 9:25 AM
IN a nutshell, some jpegs are around 30 megbytes in PhotoShop, and as saved in a folder, they are about 10 megabytes
I still don't understand this Mark. What do you mean by the size in Photoshop? Photoshop doesn't store your files, they're still stored on the drive in a folder. So we may be able to take Photoshop out of this conversation somewhat.
1) Are you saying if you open the 10 MB file in Photoshop, and re-save it folder, then it becomes 30 MB?
2) Are you saying that you have some scanned images that are large, but normal digital images processed with Photoshop and saved to a folder are small? Even though both are approximately the same
If it's number 1, I'm not exactly sure what could be happening provided the file format stayed the same. For number 2, I think it would have to be JPG compression. It can be heavily affected by noise since the compression won't work well - and film grain is pretty similar to noise, so your scan settings could play a big part too.
Posted by mark miller on September 17, 2010 at 7:07 PM
Thanks for the replies, David. Yeah, it's confusing to explain, sorry about that. Precise terminology is crucial! So, I'll make that attempt!
Good idea to keep PhotoShop out of the equation. I think your answer at the end applies and offers the solution to my original question, simply the film grain becomes 'noise' and thus affects final jpeg compression size. As an example, I am looking at a folder in windows containing identically dimensioned jpegs (12 by 18 inches at 300 dpi) originally saved at setting 12 in PS. With these and others of identical dimensions, the file sizes from what were originally slides are consistently higher, around 19 megabytes (even near 30 mb in at least one), whereas the file sizes from what were originally digital files (RAW captures) run around 7 or 8 megabytes. Occassionally, a file size from what was originally a slide, is also small, but the smaller sizes are the exception. Must be the film grain requiring lots of data that in turn affects the total file size, as you suggest. MM
Discussion
5 repliesSome of the jpeg file sizes are around 12 to 15 megabytes on some scans, which are about the same jpeg file sizes of equally dimensioned (ie 10x15 inhces at 300 dpi, 8 bit) digital files. Yet some others of the scanned images (all the same dimensions) have absolutely huge files, like 38 to 40 megabytes.
To give an example: one of my originals was a medium format. I scanned a pretty big file, as a tiff. Next I sized it to 11x14 inches at 300 dpi, 8bit depth. I saved it as a jpeg optimum out put of 12. In photoshop it is almost 40 megabytes as a jpeg, while outside of PhotoSHop in a folder, it is 30 megabytes. Another slide scanned will all the same above, is 40 megabytes in PhotoShop and about 14 megabytes in a folder, like the rest of the digitals.
I can't figure this out. I know that jpeg compressions are not all equal, but it seems they'd be closer than this. Wouldn't the final file size for equally dimentioned digital filesm whether scans from original slides, or digital originals, saved as jpegs all be somewhere about the same size megapixels?
Thanks for any feedback. MM
As a side note, I usually save my JPEG file at out put level 10 instead of 12. It gives smaller file sizes and I can't tell the difference. Of course, I saved the original master files as TIFFs.
As far as lower quality compressing, or at least to 10, where it doesn't seem to show, I still prefer saving at 12 anyway, and that's because there may be times when an end user decides to interpolate, or also, in "save as" commands, if it is saved again, more info is lost. MM
I still don't understand this Mark. What do you mean by the size in Photoshop? Photoshop doesn't store your files, they're still stored on the drive in a folder. So we may be able to take Photoshop out of this conversation somewhat.
1) Are you saying if you open the 10 MB file in Photoshop, and re-save it folder, then it becomes 30 MB?
2) Are you saying that you have some scanned images that are large, but normal digital images processed with Photoshop and saved to a folder are small? Even though both are approximately the same
If it's number 1, I'm not exactly sure what could be happening provided the file format stayed the same. For number 2, I think it would have to be JPG compression. It can be heavily affected by noise since the compression won't work well - and film grain is pretty similar to noise, so your scan settings could play a big part too.
Good idea to keep PhotoShop out of the equation. I think your answer at the end applies and offers the solution to my original question, simply the film grain becomes 'noise' and thus affects final jpeg compression size. As an example, I am looking at a folder in windows containing identically dimensioned jpegs (12 by 18 inches at 300 dpi) originally saved at setting 12 in PS. With these and others of identical dimensions, the file sizes from what were originally slides are consistently higher, around 19 megabytes (even near 30 mb in at least one), whereas the file sizes from what were originally digital files (RAW captures) run around 7 or 8 megabytes. Occassionally, a file size from what was originally a slide, is also small, but the smaller sizes are the exception. Must be the film grain requiring lots of data that in turn affects the total file size, as you suggest. MM