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 What is 50% dot in negative-film?

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aurelzki



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PostSubject: What is 50% dot in negative-film?   Thu Aug 20, 2009 6:11 pm

Hello everybody! I'm so glad that I found this site. Iím a prepress operator just here in Manila, Iím operating Accuset 1500 with Eagle Rip software.

I just wanna ask if, is the 50% dot (ellipse) in negative-film is equal to the black portion as in 50% both?
Iíve been print the calibration test to observed just the 50% by using lens only, in that way i found out that the dot and the black area were not equal (the dot is bigger than the black area in 50 percent), I immediately made a call to our supplier to check the calibration. After their final calibration tsenek ko sa densitometer (X-Rite) ang value ng 50% it was exactly 50% ang reading, pero ng sinilip ko sa lens hindi pareho ang laki ng dot at black area sa 50%. The technician told that they were relying of what the denstometerís reading.

Thereís anybody can tell me about this? I believe the densitometers because itís manufactured for that tasks and Iím sure that the densitometer we used was calibrated dahil galing ito sa supplier mismo. Ang iniisip ko lang dapat ang 50% ay 50%.

Thanks...
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tin_man

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PostSubject: Re: What is 50% dot in negative-film?   Thu Aug 20, 2009 7:38 pm

i think its because its "ellipse", so when you look at it closely the dots are not circular. And pag may pattern na yan..mukhang uneven na. As far as i know there are other dot shapes you can use in Eaglerip but ang default diyan ay "ellipse" and that is what is recommended by the RIP.
The eyes can be deceiving...gumamit nalang ng densitometer.

Just my thoughts...
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Thu Aug 20, 2009 8:04 pm

Hi Awie. Welcome to the site. Sa isang imagesetter lang ba ang problema or pareho?

If you recall when I was there your 50% on film was like 60%. Both positive and negative 50% dots should look identical....somewhat like a chessboard pattern.

Pero dahil may mga proprietary settings ang mga RIP (ie ABS, HPS, etc...) maaring di din siya mag mukhang chessboard. Dapat talaga you should have a calibrated densitometer para sigurado ka.

Maybe you can do the following if you have time:

1. Make full maintenance on your processor
2. Use fresh chemistry
3. Turn Linearization settings off.
4. If you have 2 imagesetters working, load new film on both imagesetters. Use same batch number
5. Make an exposure sweep on both devices
6. Select exposure settings separately
7. Measure the step wedge with a "CALIBRATED" transmission densitometer. See if the problem is happening on both imagesetters
8. Log measurements and average readings.
9. Create a new Linearization curve.

Better to verify your linearization settings every week. If it's out of tolerance (+/- 2%) then create a new one.

Regarding dot shape, since film-based ka pa it's better to go with Elliptical dots. Pero kung CtP ka okay mag Round dot. Magkaiba kasi ang Dot Linkup ng Elliptical and Round dots. This has great effect on your Dot Gain. Kindly see the image below. Yung nasa taas shows the dot linkup of elliptical dots while yung nasa baba sa Round.



Source:Ifra

Elliptical dots have 2 dot linkup: sa 40% dot, 1st time mag uuntugan ang dots na nasa harap and likod niya. Pag dating sa 50% dots magiging chessboard pattern siya. Ngayon, pag dating niya sa 60% naman magdidikit na din ang mga dots mo sa katabi niya na row. This means medyo mas magiging malaki ang dot gain mo sa midtone pero at least ang shadow area mo may detalye pa.

Round dot naman isa lang ang dot linkup niya....magdidikit lang ang dots somewhere between 75 to 80%. Therefore medyo mababa ang dot gain mo sa midtone pero MAGSASARADO naman ang shadows mo. If you're CTP madaling controllin ito. Pero kung film-based ka and you don't have complete control of your processes.....then sasarado ang shadow portion mo kasi meron ka pang extra 4% to 6% gain sa vacuum frame mo.

Elliptical ka na lang Awe.

My humble thoughts.

Paging Alex Dulay....any comments?


Last edited by larrysison on Wed Aug 26, 2009 10:43 am; edited 1 time in total
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presstech

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PostSubject: Re: What is 50% dot in negative-film?   Fri Aug 21, 2009 12:14 am

Hi Awie!

I just checked the densitometer used for your calibration against 2 other densitometers that just arrived 2 weeks ago; and the readings were all within 2 percentage point of each other, namely: 50%, 51% and 52%. The 52% was the reading from the densitometer used in your calibration; so the reading is on the high side compared with the other 2; but well within tolerance. High side is actually better than low side; because there's compensation for dot gain.

Furthermore, this densitometer is regularly used by us to calibrate our installed imagesetters; and we have not received any negative feedback from our clients regarding calibration. Three of them are full time service bureaus in Metro Manila that do a lot of full color outputs for printing on coated stock at 150 -175 lpi.

I have no time now to further check your observations; cause I will be out of town tomorrow up to Sunday. However, on Monday I will send someone to KPI to get a step wedge from you so that I can check it myself.

By the way, in an elliptical 50% screen the shape of the black and white areas are different; so it's somewhat difficult to visually determining if the black and white areas are the same. With square dot, it's easy because you get the checkerboard image mentioned by Larry.

Can you pm me your cel number so I can call you this weekend?
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Fri Aug 21, 2009 3:04 am

Awie and Randy,

Nabalitaan namin meron daw kayong nararanasan na quality problems sa print. My thoughts lang po:

if film density is between 3.5 to 4.0;
if density of clear film is NOT higher than 0.15;
if step wedge measurements shows linear;
then your department is okay

Pero better send your device to X-Rite for hardware calibration and recertification.

NEXT: please check your vacuum frame. di ba meron kayong plate control wedge na ginagamit? gaano katagal na ito? if you can replace it with a new one betterer di ba.

Tapos check niyo yung plate....anong step ang lumalabas...2, 3, 4, 5? May nagbago ba sa dati niyong sinusundan na step? Check the microlines. Ilang microns ang visible sa plate?

I'm not sure but during our training with Ifra for newspaper production steps 2 and 3 should be equal. 30 microns should be visible on plate. Sa GATF pang commercial production either step 4 or 5 ang sinusundan nila and 20 microns visible. I'll contact Ifra just to make sure and will get back to you.



Kung standardized naman ang film mo according to your densitometer, and also your plates according to your plate wedge....then chances are the problem is press related.....and not prepress.

Nevertheless, ang TAMANG procedure is to measure the dot gain of your press and enter it sa Eagle RIP niyo together with the ISO 12647-3 tone value curve. The RIP will compensate the discrepancies to the ISO target.

Once again my humble thoughts.

PS: Alex and I are thinking of scheduling a live chat with you guys. Please ask Feriel of I.T. to install a webcam so we can see your RIP settings. Alex can easily guide you through on what to do next. We already have the manual of Eagle RIP c/o Sir presstech. What do you think?
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Alex Dulay



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PostSubject: Re: What is 50% dot in negative-film?   Fri Aug 21, 2009 11:34 am

kung linear na nga kayo, next step is either compensate on dot gain or more adjustment sa image editing sa PS.

since na wala kayong panukat, gawa kayo step wedge sa PS na 10, 20, 30...100,then lighthen up your 50% (midtone sa curve) to make it 40%, then using the eye dropper, get the value of 10,20...100. Pasok nyo ngayon sa linearization ng eagle rip yan. eto ngayon magiging press calibration curve or press dot gain compensation. although pede rin gawin ito diretso sa eagle rip, ang purpose ko rito e para smooth ang curve.

(i know Larry is laughing sa work around na to, pero practical solution lang to, wala gamit e, hehehe)

Ibig sabihin nito yung 50% magiging 40% sa film, and etc. etc.

Awie, curious lang ako, baka yung mga ads nyo di nyo na convert sa icc profile nyo dyan na pang newspaper, you must convert it otherwise bad ang labas nyan sa newsprint. I always assume then na SWOP coated ang source profile ng mga ads unless may embedded isonewspaper26v4 ang ad from client. Use convert to profile ng Photoshop. Email mo si Larry may bagong sikreto yun sa profile to profile conversion sa PS. Brod, lahat ng ads dyan dati, ginagalaw ko, ipinapasok ko sa tamang profile. Nagmamaktol ako kapag hindi pinadaan sa akin (hehehehe).

Or, padala nyo sa kin yung mga ads nyo 3 days before publication, then i-convert ko with charge of course (hehehehe). Joke, ask ka lang question kung meron ka di maunwaan, hehehe. Ano Larry, pede na tayo outsourcing (hehehe).

Awie, tutukan mo ang proseso ng linearization, marami ka pede i-solve pag na master mo yan.

And last, yes stay with ellipse dot. Why? Basta yan ang gamitin mo, hehehe. Naipaliwanag na ni Master Larry. Para may shadow details ka pa kahit paano kahit na newsprint.

sige sunod na ulit, umaga na, tulog na ako hehehe, nangarag ako dito.
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Fri Aug 21, 2009 5:37 pm

Alex Dulay wrote:
kung linear na nga kayo, next step is either compensate on dot gain or more adjustment sa image editing sa PS.

since na wala kayong panukat, gawa kayo step wedge sa PS na 10, 20, 30...100,then lighthen up your 50% (midtone sa curve) to make it 40%, then using the eye dropper, get the value of 10,20...100. Pasok nyo ngayon sa linearization ng eagle rip yan. eto ngayon magiging press calibration curve or press dot gain compensation. although pede rin gawin ito diretso sa eagle rip, ang purpose ko rito e para smooth ang curve.

(i know Larry is laughing sa work around na to, pero practical solution lang to, wala gamit e, hehehe)

Ibig sabihin nito yung 50% magiging 40% sa film, and etc. etc.

Sanamagan! It's the 21st century, Alex. hehehe. Well, it's a workaround alright.

But seriously, Awie, please propose to your bosses to sign a Maintenance Contract with Sir Fred's company. For a small fee, they can visit your plant on a monthly basis to do linearization on both machines.

Quote :
Awie, curious lang ako, baka yung mga ads nyo di nyo na convert sa icc profile nyo dyan na pang newspaper, you must convert it otherwise bad ang labas nyan sa newsprint.


In newspaper production Awie won't have the time to do this. A workaround would be to do this in Advertising Department before editorial pages are created. Pero this is still dangerous if the artist doesn't know color management. Remember, he will be dealing with ads. And these advertisements should also match the same prints from other newspapers.

What you really need is a guy with a backbone and can stand up to your bosses and present your current situation, it's deficiencies, it's disadvantages, and risks.

Everything is pure science. Get inks according to ISO 2846-2. Get paper according to ISO 12647-3 specified L*a*b* values. Provide all the necessary tools for both prepress, press and maintenance engineers. And most importantly, allocate a huge budget to repair your ailing press. Finally, invest in training, training, training. Get somebody who knows ISO 12647-3, ISO 15076, ISO 12646, and ISO 15930 not only in theory, but in practice.

Remember, you're in this pit because of your management's failure to allocate budget for the most critical parts of your processes.
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aurelzki



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PostSubject: Re: What is 50% dot in negative-film?   Fri Aug 21, 2009 11:37 pm

thanks everyone for your prompt reply and suggestions

By the way on same issue what I am pinpointing just in 50% area because it is only the area we can determine the nearest of 50% through lens. Ang 50% dot (ellipse) area di ba dapat both the dot and black area (kung di man equal as what guys you said) dapat kabit-kabit ang row on one direction just like the image posted by sir larry, ito po kasing calibration namin ang dot area ay tagos sa kabilang row ng dot area, at ang black area ay putol-putol. kung 48% o 52% magkakabit-kabit o sasarado maski bahagya.


Sir Larry was my supervisor before and I was his Prepress support. Everytime na mag-calibrate kami sinisilip ko sa lens lagi ang 50% kaya i have a little bit idea what is the nearest to 50%. He was visited our plant 3 weeks ago he also noticed that there's something wrong on our negative.

Thanks sa inyong lahat.
Thanks sir larry for being supportive


Sir Alex,

Thanks sa mga suggestions I'll try to work on that kailangan lang ng calibration devices hehehe.


Sir Presstech,

Meron po ba kayong alam na cheaper brand na densitometer hehehe, magkano?
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Sat Aug 22, 2009 3:18 am

aurelzki wrote:
dapat kabit-kabit ang row on one direction just like the image posted by sir larry, ito po kasing calibration namin ang dot area ay tagos sa kabilang row ng dot area, at ang black area ay putol-putol. kung 48% o 52% magkakabit-kabit o sasarado maski bahagya.

Agree. Yan din napansin ko nung andiyan ako. Try printing your step wedges without linearization. Then see the difference.
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Sun Aug 23, 2009 2:59 am

Awie, dagdag ko lang. Di kaya okay yung linearization niyo nung bagong install yung RIP tapos meron nagbagong parameters sa processor niyo after the linearization?

May kinalaman din kasi dito yung Dip Time ng film sa developer section. Dip Time is yung pag lubog and pag exit ng film sa developing tray. Kung binago niyo ang processing speed niyo, and/or the temperature of the chemistry, maaapektohan nga naman ang dot size niyo dahil magbabago ang Dip Time ng film. Di ba?

If I may humbly suggest to log all the measurable parameters in your processor para standardize ang processing ninyo.

Additionally, and equally important, if your press has a "calibrated" pH /conductivity meter you can also measure your developer from time to time. Log the values once a day.

Normally ang pH ng developer section sa CTP processor nasa range ng 12 ang pH. I'm assuming ganun din sa film processor. Now, pag controlled na ang processing ninyo....that's the only time you do linearization. Otherwise, you're measuring a moving target.

Everything has to be measurable...and it should be constant. As the saying goes: If you can't measure....you can't control.

My thoughts once again.
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aurelzki



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PostSubject: Re: What is 50% dot in negative-film?   Mon Aug 24, 2009 1:11 am

Sir Larry,

Since na wala pa kaming densitometer di ko binabago ang developing time at temperature, ibinigay ni sir alex ang procedure bago umalis para mamaintain ang denstiy o para hindi mapalayo sa tamang processing at yun lang ginagawa ko.

Maliban nalang kung nagbago ng kusa ang takbo ng processor... (yan nga pala ang kailangan kong i-check lagi hehehe). Pero sa ngayon di pa naman siguro nabago dahil ng mag re-calibrate kami, fresh chemisty at pasok naman ang density sa 38 to 40.

Siguro unti-untiin ko na lang ang pagbabawas sa calibration curve then observe sa print output. cyclops
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Alex Dulay



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PostSubject: Re: What is 50% dot in negative-film?   Mon Aug 24, 2009 7:53 am

Awie,

Baka mas maigi na i-fix mo muna ang linearization mo. Kung may proof ka na linear ka, siguro pwede mo na tingnan ang plates, press, file preparation, screen angles.

Also, I want you to check if color management in Eagle Rip is activated. This is important because you don't need color management ON in RIP. Your wokflow is not color managed. You are sending a pre-separated files in your Rip (all images are in tiff cmyk). You just want the Rip to apply its screening system. You do not want to re-separate your tiff cmyk in the Rip especially if the Rip's ICC profile is configured inappropriately.

Maybe some other time, when you are comfortably well-versed with your Rip, its color management feature will be useful specifically its support for device links profiles.

Also, check if some default press calibration curve is used in your Rip setup. You also don't need it unless you do actual dot gain compensation curves which you can't do for lack of tools. You only need your calibration curve which is your linearization curve.

Your client PCD is also using EagleRip. I know you know what I meant.

Just my 2 cents. Good luck.
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aurelzki



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PostSubject: Re: What is 50% dot in negative-film?   Wed Aug 26, 2009 1:01 am

Sir Alex,

Nag adjust ako sa linearization kanina medyo may malaking diference sa dating output both parazzi and mst medyo lumitaw ang sharpness, hopefully di tsamba ang tirada kanina hehehe, observe ko muna til tom o 2 issue pa, kapag di na magbago siguro konting adjustment nalang sa linearization and image enhancement.
Thanks again sir, nakakarami na ako sayo hehehe.

Btw, naka-off ang color management at press calibration curve sa rip.

CORRECTON: the density is not 38 to 40 its 3.8 to 4.0, im apologize.
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Wed Aug 26, 2009 3:55 am

Glad to hear that. -- Alex
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presstech

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PostSubject: Re: What is 50% dot in negative-film?   Wed Aug 26, 2009 4:18 pm

Hi Guys, I just want to inform you that I got the calibration test wedge last night and measured the 50% patch with 4 densitometers. Three of them were x-rite 341 and one was a techkon (almost brand new, not ours). The readings from 3 densitometers were 49% and 1 was 50%.

The 50% may not look like 50%; but, believe me, it is 50% because the densitometer readings indicates so. If we are going to trust our eyes rather than devices like the densitometers; then maybe let's just throw away these devices and calibrate using our eyes. Hehe!

I suggest that we accept the calibrated curve as linear; because it was produced based on the densitometer readings. Rip adjustments should only be done using the eaglerip's compensation tools. This will produce the desired adjustments without changing the original linear curve. The original linear curve produced during calibration should not be tampered with because this is a standard.

After looking at several issues of the newspaper, I suggest that the only items to adjust in the rip is to put compensation for dot gain. you can start with 10% and increase gradually as needed, based on print results.

Other adjustments should be done in Photo Shop, as follows:

1. All image manipulation, up to cmyk conversion, should be done initially by one trained person. This will ensure standardization of image appearance.
2. The color limit in the PS Color Setting should be set at less than 250. The default is 300. This will bring out shadow details which are lost due to our poor newsprint quality and press deficiencies.
3. The gcr setting in PS Color Setting should be set at low. The default is medium. This will limit the black ink to the areas above 70%, effectively removing black from the flesh tones. Less black will also reduce the rosette effect; which comes out when cyan, magenta and black with dot sizes below 50% are combined.
4. Clean the colors so that primary colors (rgb & cmy) dominate the images. 3rd colors will come in to add the details in the image. Keep in mind that increasing the 3rd color leads to grayness.
5. Reducing the colors means less colors to register and will make misregistration less noticeable.
6. I also noticed images with white edges due to over-sharpening. Sharpening techniques should be properly applied.
7. For grayscale images, I suggest selecting the red channel before changing mode to grayscale. This will bring out more details and result in lighter flesh tone.
8. BTW, it is advisable to do cmyk conversion at the final stage of image manipulation.

All my suggestions are from past experiences doing consultancy for with 2 newspaper publishers; so they should work.
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Wed Aug 26, 2009 9:30 pm

There you go, Awie. Now, you can blame Randy for your troubles since it's press related. hahaha....
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Wed Aug 26, 2009 10:34 pm

aurelzki wrote:
Sir Alex,

Nag adjust ako sa linearization kanina medyo may malaking diference sa dating output

According to Sir Fred, your 50% is now linear. Dahil ba may inadjust ka na kaya naging linear? Or ito pa yung dating setting bago ka pa nag-adjust?
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aurelzki



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PostSubject: Re: What is 50% dot in negative-film?   Thu Aug 27, 2009 1:55 am

Sir Larry,

Ang ipinadala ko kay Sir Fred ay ang dating setting, yun ang final test print ng mag recalibrate kami noong August 14, minarkahan ko yun ng date.

Nag adjust ako 7 pm noong Tuesday 2 hours after pinik-up ang calibrated wedge, actually na output ko na ang ibang naunang section bago ako nakapag adjust.
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Thu Aug 27, 2009 4:52 am

Awie, that means ok naman ang RIP settings right from the start. Dapat i-blow out niyo si Sir Fred. Smile
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Alex Dulay



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PostSubject: Re: What is 50% dot in negative-film?   Thu Aug 27, 2009 10:14 am

FYI:

MST/KPPI is using isonewspaper26V4. I think they are very much aware of the newsprint parameters. Before going to standard profile, they are using PS custom separation setup base on newsprint parameters--which is one of the reasons why they had the best colors. They were also very much aware of color separations workflow, from image enhancement to sharpening technique to cmyk and greyscale conversion.

Since then, their practices had not changed. But since they had a new RIP, it was understandable that there may be some effects. This is the reason why we are asking Awie to make sure that he did a perfect linearization.

PinoyParazzi is one of the clients of KPPI. I had been with Parazzi since its day one. And it has the best layout, photo composition and color in Tabloid world in Manila. They are using PDF file submission base on PDF/x-1a specifications. I doubt it if they changed anything in their file preparation workflow which I setup. I was then actually a regular employee of PinoyParazzi.

I recommend EagleRip before I left hoping that they will get the best support...

Alex Dulay
Prepress Professional
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Alex Dulay



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PostSubject: Re: What is 50% dot in negative-film?   Thu Aug 27, 2009 11:27 am

3. The gcr setting in PS Color Setting should be set at low. The default is medium. This will limit the black ink to the areas above 70%, effectively removing black from the flesh tones. Less black will also reduce the rosette effect; which comes out when cyan, magenta and black with dot sizes below 50% are combined.

With GCR, one can actually use even maximum black generation. Removing CMY and replacing it with almost pure black will do more good than harm.

Just my 2 cents. (I was actually using this when I'm still at KPPI as one of my techniques when dealing with advertisements that needed to be re-map to newsprint color specifications).

Awie,

You are linear!

Try to use these angles: Cyan=15, Mag=75,Yel=0, Black=135. Yan ang screen angles na ginagamit ko dyan.

Also keep the halftone levels at minimum value, maybe 256? If you want more halftone levels, set resolution at 1800dpi.

Please check your screen angles at the negative. Find out if the angles are what you are expecting. There will be a bit difference because of RIP's precision screening system.

Alex
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Thu Aug 27, 2009 4:39 pm

I made a new thread "GCR Levels in Newspaper..." kasi nagmi-mixup na ang iba't ibang topics.
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Sandman

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PostSubject: Re: What is 50% dot in negative-film?   Fri Aug 28, 2009 2:25 am

Alex Dulay wrote:

Try to use these angles: Cyan=15, Mag=75,Yel=0, Black=135. Yan ang screen angles na ginagamit ko dyan.

Agree ako sa angles na yan. As per ISO 12647-3 (4.2.3) For half-tone dots with principal axis (elliptical), the nominal screen angles for C, M and K shall be 60 degrees, with the screen angle of yellow at 0 degrees and 15 degrees off from the next screen angle. The screen angle for the dominant colour should be 135 (or 45) degrees.

Should anyone decide to use a separation based on UCR, then they may want to switch the Magenta and Black angles since the Magenta will be the dominant color when going for UCR.

Quote :
Also keep the halftone levels at minimum value, maybe 256? If you want more halftone levels, set resolution at 1800dpi.

Lex, tanong ko lang. Bakit 256 lang and not 1024? PS2 pa rin ba sila? Kung PS3 di ba may supercell na yan kaya pwede ka nang magkaroon ng madaming gray levels even at or 1270 dpi. Kung may extra gray levels sila mare-reduce ang dot link-up problems nila kasi may ginagawa ang RIP sa mga dots. Instead na chessboard pattern siya sa 50% parang ganito ang lalabas:


Last edited by larrysison on Fri Oct 01, 2010 8:58 am; edited 1 time in total
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Alex Dulay



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PostSubject: Re: What is 50% dot in negative-film?   Fri Aug 28, 2009 6:25 am

Teka, bakit 256 lang. PS2 pa rin ba sila? Kung PS3 di ba may supercell na yan kaya pwede ka nang magkaroon ng madaming gray levels kahit mababa ang resolution.

Actually Sir, pang-isolate lang ito. Baka kasi nakakaapekto sa image, parang "interpolation" din kasi ito. Sa color proofing or digital printing, tamang-tama ang feature na ito. Ito lang ang paniniwala ko. Beside yung imagesetter nila capable sa 1800, 2400 and more. Why use that feature if your imager is capable naman?
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aurelzki



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PostSubject: Re: What is 50% dot in negative-film?   Sat Aug 29, 2009 5:09 am

Sir Alex n Sir Larry, try ko lahat yan, pag-aralan ko muna ng maigi para sure ang bawat galaw. Thanks uli sa inyo
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What is 50% dot in negative-film?
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