Preflight Question

[woopit@adobeforums.com]

I posted a question the other day regarding some clarification regarding dpi vs. ppi. One of the responses I received said that if you're printing a 150 line screen halftone or process image, then make sure your original digital images are at least 300 PPI. Which I thought was the case. However, when preflighting documents from outside sources I'm not sure how I can tell whether or not the image is truly 300ppi when preflighting because if I make a .ps file with a 300dpi image using my print settings... 300 res @60 line frequency then distill and open the pdf and do a preflight... it tells me that the image in the file is 150ppi. Fine, I know it's saying this because the lpi was set @60. But how would I now if someone sends me a file that has an image that is truly 150ppi.
Is there a book for using acrobat preflight?

[peter kleinheider]

Hi

If preflight is telling you the image has 150ppi then this is what the resolution is.
If preflight a PDF from a foreign source you check against the actual image resolution (can also be read as "final resolution after scaling", when it was positioned in a layout program and got scaled there)
In your case I assume 4 things:
1) the image was scaled to 200%
2) the application generating the PS file did downsample the image. To deactivate the downsampling use the "Full resolution TIFF output" option in XPress or "Send all data" in InDesign.
Sorry not being able to tell you the exact option definitions - I am running German versions of the apps here
3) Downsampling to 150 ppi in Distiller
4) Image usage in combination with Transparency and Flattening options set to 150 ppi

In terms of image resolution: It would be the optimum if an image had 300ppi for a 152lpi screening in print. In real life you will face image resolutions lower than this. Some images are anyway not that crisp resulting in no visual difference between a 300dpi image and a 250ppi image. You only should cry out loud if the image with a resolution to low looks really bad. On the other hand - not all 300dpi images are perfect ether.
When it comes to screenshots you will face images with just 96ppi. These images are perfect for their purpose and should not get touched by any upsampling or JPEG compression algorithm. This would *destroy* the screenshot.

rgds

peter

[woopit@adobeforums.com]

Hi Peter-

In response to your first statement

If preflight is telling you the image has 150ppi then this is what the
resolution is<




I did a test here by placing a 300 dpi image into a quark doc @100%. When I create a .ps file my quark output settings are... res 300 dpi, line frequency 60 lpi. After the pdf is created the preflight says that the image is 150ppi. Are you saying then that the image actually is 150ppi now because of the Quark settings that were used... or the distiller settings?

In response to your second statement

If preflight a PDF from a foreign source you check against the actual
image resolution (can also be read as "final resolution after scaling",
when it was positioned in a layout program and got scaled there)< How
can I check the actual image resolution when all they are sending me is
the pdf?




Please advise. And thanks for your help.

[peter kleinheider]

Hi woopit

When you use a Distiller-Settings that do not downsample images, then the downsampling is done by XPress. Have you found the option in the XPress printing dialog I was talking about?

Try saving the images as EPS, in this case XPress can not do the downsampling - same with RGB images. When saved as TIFF you get a CMYK separated image in PDF, XPress is doing the separation. If you place an RGB EPS image in quark, you get a RGB image in PDF.

Performing the Preflight Profile "List all images" shows you every image in a PDF. You can get more info of the images by changing the options in the Preflight Preferences found in the Preflight Options Menu.

rgds

Peter

[woopit@adobeforums.com]

Peter-

Yes, I did have the "Full Resolution Tiff Output" option checked off when I made the pdf. But, I am getting conflicting statements here. Last week I made an RGB file in photoshop brought it into quark and distilled it. It came up as CMYK in the preflight. When I questioned this on this forum I was told that Acrobat will covnert all images that were placed in a quark file into cmyk. This does seem to be the case. However, if an RGB image is distilled right out of phostohop it will be listed as an rgb file in Preflight.

I know that performing the Preflight Profile "List all images" shows you every image in a PDF. But what I am trying to ascertain is how I can be sure that what it is reporting is correct. If I understand you correctly you are saying that Quark actually is downsizing the image files thereby rendering 300dpi images into 150 ppi images as reported in preflight Is that correct? Thanks.

[peter kleinheider]

Hi woopit

Acrobat does not convert any color if the Distiller Settings you are not stating so. It is a fact that XPress converts all RGB TIFF and JPEG images to CMYK when doing DeviceN or CompositeCMYK output.

Rg. Preflight: preflight tells you the resolution of images inside the PDF file. You can trust it - it is rock solid technology. It does not lie to you.

Now make a PDF with "Full Resolution Tiff Output" checked. Now you should get a 300 ppi image in the resulting PDF (if the used Distiller Settings does not activate the downsampling of Distiller). The Resolution of the downsampling in Xpress (if the described option is OFF) is calculated by the entered dpi/lpi values. If you have them at 2540dpi/175lpi (for Adobe PDF PPD) you can be sure that Xpress will not downsample below 300 dpi.

rgds

Peter

[woopit@adobeforums.com]

Yes, Peter, Quark is doing the converting of the colors. Did I not say that? Sorry. Anyway, yes I did make the pdf correctly with the Full Resolution Tiff Output checked. I thought that I had done that B4, but I didn't. Thanks a million for all of your help. Peace Out.

[woopit@adobeforums.com]

I have built an ad in Quark that has a 300dpi tif file imported into it @ 55%. I made a ps file using the Acrobat driver and then distilled to make pdfx1a of the file. When I preflight, and check images, it says that the image is 272ppi and I'm not sure why it is saying this. Shouldn't it be a higher ppi? My settings in Distiller are set to downsample images higher than 450 ppi to 300ppi I know that the ppi and dpi are not the same, but shouldn't the final image size in this case be higher than 272ppi?
Thanks for any clarification on this.

[peter kleinheider]

Hi woopit

I assume you placed a TIFF (or JPEG) image.
Next I assume you don't have the option "Full Resolution Tiff output" activated in the XPress printing dialog.
Further I assume your screening settings where not set to 2400dpi/150lpi (at least)

In this case, XPress is doing the downsampling of the image based on the lpi settings. if they where 133ppi, the the resulting image will have around 266ppi.

You can avoid this by a popper printer setup.

rgds

Peter

[woopit@adobeforums.com]

Peter-

I am using the Acrobat Driver to make the pdfs. The default for that is set at 1200dpi/100lpi
and the Full Resolution output is not activated. The resulting image is 272lpi. Is this not a proper printer set-up? Thanks.

[peter kleinheider]

Hi Woopit

No - like I stated

2400dpi/150lpi (or more)
activate FullRes Output

Peter

[woopit@adobeforums.com]

Peter-

Got it. Thanks. U had mentioned the Full Resolution Tiff output option in a post I made about a month ago and I forgot about that...sorry. I don't understand though why the Acrobat default (1200dpi/100lpi) isn't higher. Thanks for the input.