Acrobat's Preflight and saving preferences

[rich apollo]

I was testing/playing around with some Preflight functions the other day and came up with a question. I was using Preflight to reseparate some files - to change the black generation and TAC. After the files were run through the Preflight routine some images appeared to have a much greater quantity of JPEG artifacts. Checking with PitStop seems to corroborate this. I ran the same conversions in Photoshop and did not see the increase in JPEG artifacts (increasing the quantity of black in an image can draw attention to "jpegging").

Is there somewhere to specify preferences for saving files after they've been run through a Preflight Droplet?

 

[mattbeals]

No, maybe the images were recompressed using JPEG compression when being saved after the PDF was modified.

 

[encompus]

I think Matt is correct on this. I seem to remember running into this before.

Marc

 

[leonardr]

I was testing/playing around with some Preflight functions the other day and came up with a question. I was using Preflight to reseparate some files - to change the black generation and TAC. After the files were run through the Preflight routine some images appeared to have a much greater quantity of JPEG artifacts.

What operations did you have you in your Preflight checks/fixes?

Certainly, Preflight by itself does NOT recompress anything in the file - but it is certainly possible that certainly operations that you've chosen can have that effect.

 

[Lukas Engqvist]

Lost my post by misstyping

Essentially I said any image processing (as in changing separation) would either be at a pixel per pixel or a un-jpg convert then re-jpg. Either could increase the visual disturbance of artifacts.
I would normally edit in photoshop by converting to RGB or Lab, removing noise and/or artifacts, (if time allows possibly tweak contrast with shadow highlights), reseparate to CMYK (and again if time allows add a smart sharpen).

Would be nice if a prefllight or fixup could call for an image processing script from PhotoShop, maybe a feature request there ;P

 

[rich apollo]

The Preflight Droplet runs a Preflight Profile that performs an ICC color transform and knocks out white vectors.

In playing around with it a little more, it appears that the resulting file is saved using whatever compression methods are found in the individual elements. So, Lukas, I think you hit it on the head - Acrobat is further compressing something that is all ready utilizing JPEG compression - an image that was 8.74% of original size went to 3.32%. Some other elements that used ZIP wound up using ZIP compression after the process. And if the image was uncompressed going in then it was uncompressed coming out.

PitStop can eliminate lossy compression, but I don't see a way to incorporate all of this into one Preflight Profile. One could use PitStop Profiles, but I'd like to have Acrobat perform the color transforms.

 

[michaelejahn]

ZIP is lossless, JPEG lossy

ZIP is lossless, JPEG lossy

The Preflight Droplet runs a Preflight Profile that performs an ICC color transform and knocks out white vectors.

I am certain you understand that in order for a color conversion to be applied that the image would be decompressed and then modified in its decompressed form, then recompressed. It should not be a surprise that the before and after will both be different.

If you have a JPEG image (and it is RGB or CMYK) and you modify the color of that image, or crop that image, or resample that image, the image is a NEW set of pixels- and if the image is NEW, the new needs to be re-compressed.

This recompression will absolutely be different !

If there are already JPEG artifacts, these artifacts most often will be changed as well (and I would suggest - if this is a GCR like conversion - they will most often become more prominent.

So, what to do. Of course, use ZIP and avoid JPEG. Files may be bigger, but you eliminate the degradation of multiple JPEG compression.

Another tick some use is to use images that are of higher resolution, where jpeg artifacts then become smaller - but if you have high amounts of USM, this trick might not help.

Hope this helps !

 

[rich apollo]

I can recommend the avoidance of JPEG compression to my clients, and I do, but that doesn't mean that they'll do it. And, JPEG compression is in ALL the Adobe PDF defaults.

I have said before, "JPEG compression is the 'kiss of death' in print".

 

[mattbeals]

So then as part of your preflight profile in PitStop switch all NON ZIP compressed images to ZIP compressed and solve that problem. As for having Acrobat perform the color conversions as part of your PitStop processing that just won't happen. If you need a plug-in that can preflight and fix AND do a better job of converting colors then look to Callas pdfToolbox 4.