Transfer Function

in article , Aleksei Guzev at
wrote on 11/26/03 11:51 PM:

Hi,

While exporting from PhotoShop to EPS, what functions does control option "Include Transfer Function"?
Can one adjust the function? Do the function reside in PSD file or it’s a print setup option?

—
The transfer function is a curve (or curves) applied to a file to compensate for output to specific printers. You use it as you do the "Curves" function, but it applied when the file is sent to print.
– Be aware, however, that if you supply a file with a transfer curve applied and saved – when this is processed by your prepress department, your curve will be applied (generally – but not always) in combination to the curves they have set up for their imagesetter/platesetter — basically destroying the file.

MSD

On Thu, 27 Nov 2003 18:27:39 GMT, WharfRat
wrote:

in article , Aleksei Guzev at
wrote on 11/26/03 11:51 PM:

Hi,

While exporting from PhotoShop to EPS, what functions does control option
"Include Transfer Function"?
Can one adjust the function? Do the function reside in PSD file or it’s a
print setup option?

—
The transfer function is a curve (or curves) applied to a file to compensate for output to specific printers. You use it as you do the "Curves" function, but it applied when the file is sent to print.
– Be aware, however, that if you supply a file with a transfer curve applied and saved – when this is processed by your prepress department, your curve will be applied (generally – but not always) in combination to the curves they have set up for their imagesetter/platesetter — basically destroying the file.

MSD

Thank You very much. But I do understand what are the functions, but how can one adjust them in Photoshop?

Aleksei Guzev

WharfRat …

in article , Aleksei Guzev at
wrote on 11/26/03 11:51 PM:

Hi,

While exporting from PhotoShop to EPS, what functions does control option "Include Transfer Function"?
Can one adjust the function? Do the function reside in PSD file or it’s a print setup option?

—
The transfer function is a curve (or curves) applied to a file to compensate for output to specific printers. You use it as you do the "Curves" function, but it applied when the file is sent to print.
– Be aware, however, that if you supply a file with a transfer curve applied and saved – when this is processed by your prepress department, your curve will be applied (generally – but not always) in combination to the curves they have set up for their imagesetter/platesetter — basically destroying the file.

MSD

Are you sure that this will happen if the files are already in CMYK ? IMO the conversion is already done and specific curves for the imagesetter should just compensate minor machine errors.
Why do we have the option to embed Transfer Functions ?
Just to show e.g. UCR /GCR ?

Best regards –Gernot Hoffmann

Are you sure that this will happen if the files are already in CMYK ? IMO the conversion is already done and specific curves for the imagesetter
should just compensate minor machine errors.
Why do we have the option to embed Transfer Functions ?
Just to show e.g. UCR /GCR ?

A customer said that a printer made wrong reproductions from his files. His files were Photoshop PSD in CMYK. I opened the files. The first impression was that the pictures were desturated very much. I saved Photoshop PDF. PDF looks just like PSD. Then the customer told he is sure that saturation is lost due to "all Adobe’s programs have an error for years". He stated his files contain pictures with good saturation. He asked me to export a picture to EPS. I had done this, and, of course, I had turned OFF the option "Include Transfer Function". Then a had distilled the EPS. The second PDF had about 90% of cyan at the point, where source PSD had only about 50%. It’s surely a kind of color correction, but I did not embed any profiles. Then I exported the picture to EPS with the option turned on. The third PDF was equal to the source PSD and the first PDF. I think the option should be turned on to get good results. But what function does Photoshop embed I do not know.

What the customer had done to alter the functions? And what functions had he altered?

Aleksei Guzev

Aleksei Guzev …

Are you sure that this will happen if the files are already in CMYK ? IMO the conversion is already done and specific curves for the imagesetter
should just compensate minor machine errors.
Why do we have the option to embed Transfer Functions ?
Just to show e.g. UCR /GCR ?

A customer said that a printer made wrong reproductions from his files. His files were Photoshop PSD in CMYK. I opened the files. The first impression was that the pictures were desturated very much. I saved Photoshop PDF. PDF looks just like PSD. Then the customer told he is sure that saturation is lost due to "all Adobe’s programs have an error for years". He stated his files contain pictures with good saturation. He asked me to export a picture to EPS. I had done this, and, of course, I had turned OFF the option "Include Transfer Function". Then a had distilled the EPS. The second PDF had about 90% of cyan at the point, where source PSD had only about 50%. It’s surely a kind of color correction, but I did not embed any profiles. Then I exported the picture to EPS with the option turned on. The third PDF was equal to the source PSD and the first PDF. I think the option should be turned on to get good results. But what function does Photoshop embed I do not know.
What the customer had done to alter the functions? And what functions had he altered?

Aleksei Guzev

Aleksei,

perhaps this issue can be clarified with help by others.

1. If the CMYK image looks bleached in PhS then it´s probably spoiled.

2. PDFs should be made generally by
"Input file None",
"Leave Colors unchanged",
"Rendering Intent Default".
This guarantees an unmodified transport of colors by original numbers.

3. After reading the PostScript Language Reference Manual: A transfer function is a tone reproduction curve for an output device, here a CMYK printer.
This would make sense for an uncalibratated laser printer – the output values are tweaked for compensating dot gain or for better appearance. In this case "PostScript Color Management" should be checked (On). If the file is already in CMYK, generated from an RGB image by an appropriate CMYK profile (Euroscale Coated) then a further transfer function would be quite useless.
I would use "Don´t embed transfer functions" and for Export as EPS "Don´t use PostScript Color Management".

Everything "IMO", can be corrected.

Best regards –Gernot Hoffmann

Why do we have the option to embed Transfer Functions ?
Just to show e.g. UCR /GCR ?

A transfer function is NOT a black generation function. It has nothing to do with UCR/GCR or black generation.

It is a curve, identical to the Curves command, that is recorded inside the EPS and is applied to the image when it reaches the printer.

You set the transfer function using the Page Setup command in Photoshop.

—
Rude T-shirts for a rude age: http://www.villaintees.com Art, literature, shareware, polyamory, kink, and more:
http://www.xeromag.com/franklin.html

Then the customer told he is sure
that saturation is lost due to "all Adobe’s programs have an error for years".

Speaking as a prepress professional who has used every version of Photoshop since Photoshop 1.0.7 in a professional prepress and printing environment:

Your customer is full of crap. He has absolutely no idea what he’s talking about.

What the customer had done to alter the functions? And what functions had he altered?

Open the PSD file and go to File->Page Setup. Hit the Transfer… button to see the transfer function he created. Prepare to be shocked and amazed; it sounds to me like he created his images with poor saturation (probably on account of a poorly-calibrated monitor), then used a radical transfer function to slam the image’s color around on output.

—
Rude T-shirts for a rude age: http://www.villaintees.com Art, literature, shareware, polyamory, kink, and more:
http://www.xeromag.com/franklin.html

On 28 Nov 2003 19:24:28 GMT, Tacit wrote:

Then the customer told he is sure
that saturation is lost due to "all Adobe’s programs have an error for years".

Speaking as a prepress professional who has used every version of Photoshop
since Photoshop 1.0.7 in a professional prepress and printing environment:

Your customer is full of crap. He has absolutely no idea what he’s talking
about.

That’s right, but I had not told that to him, guess why! ;)))

What the customer had done to alter the functions? And what functions had
he altered?

Open the PSD file and go to File->Page Setup. Hit the Transfer… button to see
the transfer function he created. Prepare to be shocked and amazed; it sounds
to me like he created his images with poor saturation (probably on account of a
poorly-calibrated monitor), then used a radical transfer function to slam the
image’s color around on output.

It’s just what I told him.

But I do not see the "transfer…" button. Photoshop 7.0.1, PC There is a button labeled "Transfer…" in the Print dialog, but the function set to be a unit matrix there.

Maybe the file was not created with Photoshop? Some other program could export the picture to PSD format and set the curves.

Aleksei Guzev

On 28 Nov 2003 07:57:37 -0800, Gernot Hoffmann
wrote:

1. If the CMYK image looks bleached in PhS then it´s probably spoiled.

How could one detect if the file is damaged?

3. After reading the PostScript Language Reference Manual: A transfer function is a tone reproduction curve for an output device, here a CMYK printer.
This would make sense for an uncalibratated laser printer – the output values are tweaked for compensating dot gain or for better appearance. In this case "PostScript Color Management" should be checked (On). If the file is already in CMYK, generated from an RGB image by an appropriate CMYK profile (Euroscale Coated) then a further transfer function would be quite useless.
I would use "Don´t embed transfer functions" and for Export as EPS "Don´t use PostScript Color Management".

Everything "IMO", can be corrected.

We use the "don’t"s because we use calibtrated imagesetter and do not need the curves.
That is why neither we nor our colleagues from another printer did not notice the missaturation on a definitely abstract picture. If it were a newspaper portrait or a landscape we would, of course, detect the problem. Although I was feeling that something is wrong with the picture, if the customer did not said about this issue, we could printed the picture as it was.

Aleksei Guzev

(Tacit) wrote in message news:…

Why do we have the option to embed Transfer Functions ?
Just to show e.g. UCR /GCR ?

A transfer function is NOT a black generation function. It has nothing to do with UCR/GCR or black generation.

It is a curve, identical to the Curves command, that is recorded inside the EPS and is applied to the image when it reaches the printer.
You set the transfer function using the Page Setup command in Photoshop.

Tacit,

not excactly. Accoording to the PLRM, the curves are not applied to the image. They are applied between the CMYK output of the image (which may be in RGB for many printers) and the CMYK inputs for the printing machine.
This allows to manipulate e.g. tints on laser printers.
Quite useless IMO for any kind of prepress work for imagesetters.

Thanks for the clarification about UCR/GCR.
Theoretically it would be possible to tweak ready CMYK images as well, but this would cause a lot of confusion…

Best regards –Gernot Hoffmann