question with photo engaving

[Chad Fitzgerald]

i convert my photos to b&w stucci, either 250 or 380 dpi depending on the material.
ive been getting verticle lines(has the appearance the laser missed) evenly spaced. seems to be most noticable oin the 380 dpi.
the lines are somewhat faint, but noticable. problem is it isnt on every pic.
i often use photos with low dpi to start and increase dpi, also i sometimes enlarge them.
would either of these be the issue. could it be how stucci converts it?
tried taking pics but yet to be able to get a photo to show it. i can keep trying if necessary.
thanks
chad
here is a pic dont know if you can see it
IMG_0295.JPG

[Richard Rumancik]

Chad - Are you certain that you are plotting at the same resolution as the photo? ie make sure you have the laser set to 380 if that is the photo resolution.

Upscaling a photo is not the best thing to do. I understand sometimes you have no choice. Better to ask for a better photo when possible. You might need to research the topic or upscaling and get some ideas. I saw some info on a PhotoShop tutorial where they upscaled 5 or 10% at a time and did this a few times - apparently to reduce artifacts etc. I'm no expert on this . . .

I can see a faint white vertical line starting at about the 7:30 position. I doubt it is a problem with using Stuki. Is your source a jpg? If so make sure you turn off all compression while working on the file - or convert it to a tif before you even start any edits and resampling.

One thing you might try - rotate the existing bitmap file 90 degrees and plot to see if the line rotates. If it does I'd say the file has an artifact from a process run on it. If it is still vertical then I'd think it is banding - the cause of which could be many things, including hardware such as bearings. Maybe do a search on this forum on "banding" and see what comes up.

[Larry Bratton]

Chad,
You say you convert them to 250 or 380 etc. What resolution are you starting out with? The photo needs to be of sufficient resolution to start with, you can't just take a 72dpi photo and change the resolution and expect that to work, it won't. Even if you have a decent photo you need to use proper software and procedure to make those changes.

[Ross Moshinsky]

I really don't think people understand DPI. DPI doesn't exist on computers. DPI is just a conversion/scaling factor for resolution.

Taking a 10"x10" 72dpi image and shrinking it to 5"x5" makes it a 144dpi image. It's exactly the same thing. People get way too caught up in DPI with lasers. DPI becomes very important in large format printing because you need that extra information. On a 3"x3" image, DPI is relatively insignificant. The quality of the image is far more important.

[Martin Boekers]

I can't tell you how many times someone sends me a screen shot (72dpi) and says it looks great on my computer......

So yes DPI does matter! Yes you can "res" up an image by "resampling" at a higher DPI, and it will help, it won't make it
a great image but it will help. You can have a nice quality image that will not look good at it's engraved or printed resolution
so It's hard to say that quality alone will make it better. Chances of "banding" or creating "artifacts" are definitely greater if the
image is not the same resolution or a direct multiple of it. If you want to do a test, take an image and laser at 3 different resolutions,
then you should see the difference. Take the above example. I think you will see a difference if you engrave a piece 10x10 at 72 DPI
an one at 5x5 at 144 DPI, there will be a visible difference. Now, if you want to talk "viewing distance that is a whole different discussion...

[Ross Moshinsky]

I can't tell you how many times someone sends me a screen shot (72dpi) and says it looks great on my computer......

So yes DPI does matter! Yes you can "res" up an image by "resampling" at a higher DPI, and it will help, it won't make it
a great image but it will help. You can have a nice quality image that will not look good at it's engraved or printed resolution
so It's hard to say that quality alone will make it better. Chances of "banding" or creating "artifacts" are definitely greater if the
image is not the same resolution or a direct multiple of it. If you want to do a test, take an image and laser at 3 different resolutions,
then you should see the difference. Take the above example. I think you will see a difference if you engrave a piece 10x10 at 72 DPI
an one at 5x5 at 144 DPI, there will be a visible difference. Now, if you want to talk "viewing distance that is a whole different discussion...

Low quality and low DPI are not the same thing. Computers don't know DPI. Computers know resolution. DPI is just a piece of information stored in the file to provide a scaling factor. There are no "dots" on a computer screen or in a digital file. There are only pixels. When you "res up" an image, you're increasing the resolution of the image. You're not changing the DPI. DPI is just a way to express the difference between digital media and "printed" media.

[Martin Boekers]

Low quality and low DPI are not the same thing. Computers don't know DPI. Computers know resolution. DPI is just a piece of information stored in the file to provide a scaling factor. There are no "dots" on a computer screen or in a digital file. There are only pixels. When you "res up" an image, you're increasing the resolution of the image. You're not changing the DPI. DPI is just a way to express the difference between digital media and "printed" media.

I guess it my photo background kicking in, but yes, you can have a poor quality image, out of focus, bad exposure etc.
and giving it more information (Pixels Per Inch) may not help it. I do understand that computers use pixels and not dots
per say. I see when I resize an image in PS I have a choice to resample or not. If I choose not with 10x10 at 72PPI and change it to 5x5 the PPI becomes 144, now when I tell PS I want to resample 10x10 at 144PPI it interpolates the 10x10 and
at that size there is now more information in the file. My Epilog fires dots and I set it for what DPI I need. The less DPI I
engrave at, the less information the file is engraved at. So yes we can discuss terminology.
In the printing industry Dots or in some case shapes where burned to films, pretty much standard. The one thing I don't believe has changed is that the more information that is in an inch, be it pixels or dots the more information will be included
in the engraving if set properly in the print driver. If I have an image say 5x5 at 72PPI and print it at 300 it would visibly less
quality than if I started with an original image that was 5x5 at 300PPI. The thing I suggest is find a standard quality size that works for you, One of the first things I do for new employees is have them do a series of tests, First is text, I have them engrave it at 150, 300, & 600 DPI (Epilog) so they can see the difference, then I have a file with an image and do the same thing, the final being a 3 copies of the same image shot at hi, med, and low resolution, They engrave all 3 at 600DPI so they can
see the difference. It's easier to see then to have a non graphics person understand the concepts. The next stage is understanding compression and what happens as you save a file over and over as it loses some of its detail through interpolation. All this is why engravers should get graphic education along the way to understand how to optimize their work.

[Michael Hunter]

Some of these threads are getting far too technical to be of help to the posters of the original questions.

Martin's comments may not be technically correct, but it is the case that most computer users seem to use the terms dpi and ppi interchangeably and most (including me) will understand EXACTLY what he is on about.

Similarly, in the thread about lenses, the original poster (who apparently did not really understand much about lenses at all) has now been presented with drawings which, while technically correct, cannot be properly explained without getting deep into the maths and physics of the properties of lenses.

Whilst not condoning incorrect answers in any way, it should be possible to answer questions in a way understandable to the original poster and this may mean using a simpler "models" to explain things or using terms like dpi in their "everyday" usage.

[Chad Fitzgerald]

for this photo, came off FB, came in at 72, changed to 380. i had run this same photo pn tile with no issues. this time(begining from original) on changed to 380, increased size, and got the verticle lines.(you can barely see one just to the right of her ear.
how do i turn off compression??
sounds like maybe if im making the image larger, this may be doing it.
i do believe its something in my process causing it, not the laser, simply because only happens with some photos. And any time it does happen, the vert lines are spaced perfectly across the pic. 7/8" gap in this one.
i also understand the 72dpi pics are not ideal. i use these when practicing new stuff, with friends and family pics. I guess im trying to figure out what causes it in order to avoid problems on real jobs.
here is what i do
import pic, crop pic, resample to either 250 or 380 dpi and change size as needed.
adjust image brightness, etc, convert to BW stukki.
thanks for the help

[Michael Hunter]

import pic, crop pic, resample to either 250 or 380 dpi and change size as needed.

Try doing the RESAMPLE step LAST. I think that that may solve your problem.
If you alter the size after resampling, you loose the relationship between the picture resolution and the dpi set on the laser.

[Dee Gallo]

Try doing the RESAMPLE step LAST. I think that that may solve your problem.
If you alter the size after resampling, you loose the relationship between the picture resolution and the dpi set on the laser.

I agree with Michael. I'm no expert, but I always start with the photo at the correct size before playing with it. Seems to work for me.

[Bruce Dorworth]

I am not sure I understand this process. Every picture that I take with my digital camera comes up at 72 dpi. Does that mean that you have to use it at 72 dpi or can you resample this image?

Bruce

[Mike Null]

Bruce

Your camera should have a range of resolution options.

[Dan Hintz]

I am not sure I understand this process. Every picture that I take with my digital camera comes up at 72 dpi. Does that mean that you have to use it at 72 dpi or can you resample this image?

Bruce

This is merely an artifact of desktop publishing programs... ignore the dpi value attached to the image. Simply look at the area you have to work with and make sure the resoltuon of your image fits that area when printed at the resolution you want. For example, if you have a 2"x3" area that you wish to print at 300dpi, your image should be 600x900 pixels.

[Mike Null]

Dan

Do you want to elaborate on that? My camera resolution is what I get when I download the images to my computer. That resolution remains until I choose to alter it with PhotoPaint.