JPG and TIFF - driving me mad!

[Westend_jon]

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Hi

 

I've just had a black and white 35mm film processed and scanned here in the UK

 

The advertised service is an 18mb scan per image

 

However the file that I received is about 2MB - it's a jpg

 

I've queried the file size and have been told that it's scanned to produce an 18mb image and that this is saved as a jpg

 

My understanding is that jpg is a lossy format and that the 16mb of data from the scan have been lost in the compression process

 

The company insists that the file is the same as the 18mb scan and that if I save as a tiff it will revert to 18mb

 

And so it does - but it looks like the original 2mb image

 

My understanding is that jpgs can't be uncompressed and that the tiff is bigger because it's a less efficient file store

 

What am I missing? Am I wrong?

 

 

 

Regards, Jon

 

PS the Company will save as a tiff on request and to be fair they have put up with my questions all day so although not named I think they are a good company - I just don't follow their logic. 

 

 

[dpitt]

Jon,

 

There is some confusion here between MB (file size) and MP megapixels (picture size)

 

1. Advertising for scans is done in MP, so 18 MP means that if you multiply number of pixels H x number of pixels in with it should be approx 18 mo e.g. 5212 × 3468

 

2. File size is not to be confused with pixel size! One could compress 18MP in a file only 2MB in size . And it will mean some loss in quality.

With jpeg special care needs to be taken to not save modifications sequentially. Each compression and save will cost extra quality and will produce artifacts, often after 3 to 4 saves.

Good editors like LR , Capture One and Aperture will keep the original and apply changes in memory so that JPEG compression only happens once for each export.

Ineffecient but lossless files like TIFF will be large for the same amount of MP, but they can be saved multiple times without loss of IQ.

 

JPEG will always be 8bit colors, but other than that it can be quite high in quality. When processing starting from 16 bit files are preferred.  (can only be had as TIFF or other lossless formats) But in the end it is always compressed to JPEG 8 bit before printing. So as long as you edit the JPEG scan with a good editor, it should be usable.

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[Westend_jon]

Hi - the company in question advertises their scans in terms of mb not megapixels

 

They offer 18mb scans but deliver 2.5mb files

[earleygallery]

I would ask them to rescan and send you the TIFF files. 

[250swb]

 

What am I missing? Am I wrong?

 

 

 

I think it is perhaps a bit of an overreaction. OK, if you wanted TIFF files they should have sent you them. But a JPEG is only lossy if you keep opening, editing, and saving it time after time. The first time opened any loss will be utterly insignificant from the image quality you could have got from an uncompressed TIFF, hence the company saying to save the opened JPEG as a TIFF, and this would be normal procedure if wanting to edit any JPEG. I don't think the company are trying to rip you off or anything, after all they will send out files to customers who have varying degrees of memory available so 2mb JPEGs (72mb for a roll of 36) are a convenient usable method instead of for instance dumping on an iPad user 648mb of TIFF data in one go.

 

Steve

[jaapv]

That sounds reasonable, as the iPad user is unlikely to do much editing, but starting off as a jpg is rather limiting for postprocessing.

2MB jpgs are not very useful for printing to a large size either.

As a comparison, the  8-bit jpg from an M240 file will often be 12 MB or larger, depending on the image content.

An 18 MB TIFF file from a scan is not very big either.

[philipus]

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I don't think it is an over-reaction at all. I would also have been disappointed if I had expected 18MB scans.

But a JPEG is only lossy if you keep opening, editing, and saving it time after time.

 

Well, when saving a tiff to jpeg image information is lost so it is not only when one keeps opening and saving (I am also aware of the tests done in this respect which show only little image degradation).

 

I'd go back and request 18MB scans. It is true the jpeg format has improved a lot and can (depending on how compressed it is) take quite a bit of post-processing. 

[mark_r_sf]

I believe dpitt's comments on the MP/MB confusion are probably the source here. 

But, no, saving a 2mb jpg to a tiff will not recreate more data as a 18mb tiff. If it's not in the file you can't create it by re-saving it.

[wattsy]

I am also aware of the tests done in this respect which show only little image degradation

 

Isn't that the important point, Philip?

 

The easiest thing to do is for the OP to test for himself. Take a TIFF file of roughly 18mb size (approx 3000 x 2000 pixels in 8-bit) and save as a jpeg of around 2mb (approx quality setting 11 in photoshop). Open this jpeg file and place as a layer on top of the open TIFF file. Switch the jpeg layer to 'difference' view and see the resulting difference in the file quality. It will appear black which indicates that the two layers are effectively identical.

[philipus]

In my experience a 16 bit tiff holds up better in post than a jpg does but it all depends on what one does and one's expectations /needs.

[Westend_jon]

Isn't that the important point, Philip?

 

The easiest thing to do is for the OP to test for himself. Take a TIFF file of roughly 18mb size (approx 3000 x 2000 pixels in 8-bit) and save as a jpeg of around 2mb (approx quality setting 11 in photoshop). Open this jpeg file and place as a layer on top of the open TIFF file. Switch the jpeg layer to 'difference' view and see the resulting difference in the file quality. It will appear black which indicates that the two layers are effectively identical.

 

Thanks - I don't have photoshop but can follow the argument and would expect the result to be as you describe. I tried saving a small jpg to tiff and side by side they look identical on screen when blown up. 

 

 

Regards, Jon

[Westend_jon]

I think it is perhaps a bit of an overreaction. OK, if you wanted TIFF files they should have sent you them. But a JPEG is only lossy if you keep opening, editing, and saving it time after time. The first time opened any loss will be utterly insignificant from the image quality you could have got from an uncompressed TIFF, hence the company saying to save the opened JPEG as a TIFF, and this would be normal procedure if wanting to edit any JPEG. I don't think the company are trying to rip you off or anything, after all they will send out files to customers who have varying degrees of memory available so 2mb JPEGs (72mb for a roll of 36) are a convenient usable method instead of for instance dumping on an iPad user 648mb of TIFF data in one go.

 

Steve

 

I think it is perhaps a bit of an overreaction. OK, if you wanted TIFF files they should have sent you them. But a JPEG is only lossy if you keep opening, editing, and saving it time after time. The first time opened any loss will be utterly insignificant from the image quality you could have got from an uncompressed TIFF, hence the company saying to save the opened JPEG as a TIFF, and this would be normal procedure if wanting to edit any JPEG. I don't think the company are trying to rip you off or anything, after all they will send out files to customers who have varying degrees of memory available so 2mb JPEGs (72mb for a roll of 36) are a convenient usable method instead of for instance dumping on an iPad user 648mb of TIFF data in one go.

 

Steve

Thanks - they will send tiffs on request so that's not an issue. The issue is that a 2mb jpg is not a good starting point for any post processing and it's a long way from the 18mb file that's advertised. I get 18mb files from my M9 when set to .dng so I was kind of expecting a similar level of image quality.

 

 

Regards, Jon

[250swb]

I get 18mb files from my M9 when set to .dng so I was kind of expecting a similar level of image quality.

 

 

Dream on.

 

First of all a 2mb JPEG is the same as an 18mb TIFF, it is just compressed information. Have no illusion, you are not being short changed save for the fact that you'd want to edit the opened JPEG as a TIFF file, and it wouldn't be 16 bit. There will be no discernible difference in image quality.

 

Second, and 18mb TIFF scan is actually a medium sized scan for 35mm, I'd expect 34 MB at a good scanning resolution. But in either case you will not, repeat not, get a 'similar level of image quality' as your M9. You will get excellent image quality if your post processing skills are up to it, but it is a different image quality and not the same as digital, hence many peoples preference for using film.

 

Steve

[pop]

First of all a 2mb JPEG is the same as an 18mb TIFF, it is just compressed information.

I just did a spot check on my disk.

 

Case 1: Saving a tiff-image with the GIMP as a jpg-image with the quality set to 100% will yield a jpg file which is about a third the size of the original tiff file.

 

Case 2: Setting the quality to 90% will yield a jpg file which is about an eighth the size of the original tiff file. The differences between the image in the tiff file and the image in the jpg file are visible but not - in any of the cases I observed - drastic. Areas with little structure and small differences in tonal values become featureless blobs. Other areas exaggerate structures which are but barely visible in the tiff. 

 

Whether these differences do matter to you or not depends on the individual case and your preferences, of course, but they are readily visible at that compression rate.

[250swb]

 

Whether these differences do matter to you or not depends on the individual case and your preferences, of course, but they are readily visible at that compression rate.

 

Yes, but we don't know what the compression was set at so have to assume a ballpark figure, but a print won't show up any degradation even though you can see some pixel peeping. And given a film image is all grain anyway you'd have to also assume the image was made with perfect technique, perfectly processed film, and perfectly scanned, before any small degradation in the JPEG has a greater effect on the image quality than any of those. In other words there are plenty of other things that can degrade the image before you worry about the JPEG compression. The OP is stuck with JPEGs for the time being, I'm just pointing out the TIFF files when they arrive won't be, or at least shouldn't be, a great deal different.

 

Steve

Edited July 3, 2015 by 250swb

[pico]

Examining a JPEG or any format on your screen is unlikely to be an adequate representation of a print. When I open a JPEG it is uncompressed in the process, no?

 

When sent to a printer I have no idea of what the printer driver does to it. Does anyone?

[FredR]

Ya gotta love film.

 

Fred

[Broadside]

These seem pretty low-res scans to start with. Scans (jpeg) from my local Tesco come in at 1.5Mb per neg, no better than cheap 6x4 prints in quality.

Scans from my Minolta Dimage Scan Dual IV come in at around 70Mb tiff for each colour neg. Quite a difference.

[Westend_jon]

Examining a JPEG or any format on your screen is unlikely to be an adequate representation of a print. When I open a JPEG it is uncompressed in the process, no?

 

When sent to a printer I have no idea of what the printer driver does to it. Does anyone?

As far as I know jpg is a lossy compression process - in other words data is stripped from the image and thrown away - it's never going to come back. A jpg file will never get bigger and that's the issue with this processor. They advertise 18mb scans but deliver 2mb files. 

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[fiftyonepointsix]

Baseline JPEG performs a discrete Cosine transform and uses Huffman code to store the frequency coefficients. The Huffman coding process usually produces a 2:1 to 3:1 reduction in file size. The Discrete Cosine transform is reversible, so if all of the coefficients are saved- the only loss would be in round-off error, which is "in the noise". Loss occurs when the high-frequency components are tossed out to get more reduction in file size.

 

In the case of 2MBytes being required to store an 18MPixel scan- lossy compression was used.