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Brian Robison
01-25-2007, 11:00 AM
I have some one sending me HUGE jpeg files to laser but they are at 300 dpi. These pictures are 15077 x 19139 and 8582 kb. Is there a way to reduce the picture size and get a better than 300dpi resolution?

Thanks

Joe Pelonio
01-25-2007, 11:18 AM
Is your question based on the download time, or time to send from the computer to the laser? A jpg file loses resolution every time it's saved.
If you want a truly high resolution file then a tif is much better. The problem
is that tifs are even larger files.

Not as often with laser work but more so with large format digital printing, I'll require that either the customer send me an original photo that I can scan, or the file on CD or DVD. For most of my laser work 300 dpi scans are satisfactory, and come from graphic designers who have the software (like photoshop) that will allow them to size it at the actual size to be engraved at the same resolution at less than 1MB.

Brian Robison
01-25-2007, 11:33 AM
Hi Joe, thanks for your responce. I need something really good for the laser. Lots of greyscale in these photos. I'd love to have them in a vector format but he already has around 100,000 of these jpegs and he's not going to change them. Shame really, they were all drawn Photshop and could have been saved in a vector format.
I guess I just resize them when I get them and go from there.

Bill Cunningham
01-25-2007, 11:59 AM
Once you work on them, remember to 'never' re-save them as a .jpg
use .tif

Tom Henry
01-25-2007, 12:32 PM
hmmm.. As someone who worked in photoshop on a daily basis it is known that if you reduce the amount of pixels you lose quality. I used to deal with everything from billboards to very high end magazines. Tell me what you need and I will tell you if you can achieve it.

As far as jpeg goes... we NEVER saved out as jpeg. If you want to save a file and want to compress it which you really shouldn't do if you are concerned with quality, we used to use the .eps format and in the compression section choose which one you want. Even then you lose quality.

You can PM me and I can help you out if you would like.

Lee DeRaud
01-25-2007, 12:42 PM
Doesn't PNG have a lossless compression option?

Brian Robison
01-25-2007, 1:30 PM
This potential customer has around 100,000 jpegs already saved and of course he's not going to redraw them. I'm only going to get the large jpegs. They should work just fine for the laser I guess. I just tend to be a little picky when it comes to quality. I need to take these huge jegs and save them as something more usable. If I import them directly into Corel the files will be so large that it will take several minutes to process. So, size and type of files to use would be helpful. Something that works well with Corel 12.

Bill Cunningham
01-25-2007, 1:48 PM
I would assume that you will not be using them in the huge size provided (15077 x 19139 pixels= 50" x 60" @ 300ppi) Unless you are reproducing photographic posters, I would resample them to the size you require for the final work, and save them as a greyscale .tif file.. , a smaller physical size = smaller file.. If you use .tif compression, it will not compromise the quality of the file, because it compresses using an alogorythm.. .jpg's reduce file size by actually 'removing' parts of the file, never to be recovered..

Aaron Koehl
01-25-2007, 1:49 PM
I've had great luck with .PNGs

Brian Robison
01-25-2007, 2:00 PM
How do you know what size to make it? I'd like it 18" x 12"

Tom Henry
01-25-2007, 2:11 PM
What resolution are you trying to achieve?

Bill Cunningham
01-25-2007, 3:06 PM
How do you know what size to make it? I'd like it 18" x 12"
If your working in corel draw, from the bar at the top, select Bitmaps, resample, and you will see where you can enter the size you would like it to be, and below is the current dpi. don't change the dpi, and make sure you have a check mark beside 'maintain aspect ratio' and then click OK You may not get exactly 18 x 12 because you 'have' to maintain that aspect ratio, or things will get weird..

In photopaint, click image on the top bar, click resample, and you get the same little box to enter your changes...

Brian Robison
01-25-2007, 3:18 PM
I think that aswers my question. It now says my dpi is almost 1800! Sorry I had such a hard time explaining it.
I should be able to import the 300 dpi huge jpeg and shrink it down. Change the dpi to around 600 and be happy! Thanks.

That took my file size down from 51 mb to 7, yipee!

Rodne Gold
01-25-2007, 11:56 PM
All you have to to is resize the file , FORGET dpi , think PIXELS . To get the size you need resize the file to the size it's gonna be engraved at 300 pixels per inch , anything more is a total waste and even that is overkill for a laser , you can get away with 200 Pixels per inch. The laser cannot resolve more than 100 pixels per inch anyway.
Saving as a JPEG is fine for lasering , there is almost zilch quality loss and even if there is , your output device is a gross printer at best. No one barring pro stock agancies or the top of the range mags etc , want stuff like tiffs - unwieldy unmanegable files.
I don't possibly know what your customer was thinking or how he got those files or what he can possibly do with them , my Canon 5d Camera is a 12 mpix (3000 pixels x 4000 pixels) camera and its good enough for any pro to shoot with and even the top medium format digital pictures are 40 mpix , round 6000 x 6000 pixels and even with my 12 mpix cam , I can print the pic as big as I want up to ANY billboard size.(I have large format printers and do so regularily)

Bill Cunningham
01-26-2007, 11:39 AM
I don't know if X3 renders files differently than 12, but you can 'think' in pixels all you want, corel resampler only specifies dpi even if your page is set-up as ppi. so unfortunately, your are 'forced' to think the way your software works or at least depicts the changes.. .jpg's are web files! Saving working files in a substandard format like .jpg makes no sense other than for use on the web.. Memory is cheap, the average dvd will hold hundreds of 7 meg files, the average h.d will hold thousands, and the processor speeds today, make the loading time of a large file pretty well insignificant.. If you are etching or engraving from a .jpg (or any other greyscale for that matter) you are going to get halftones, even the areas which look solid black are going to have 'fuzz' around the edges. For a proper job, they must be true black and white (there is no such thing as a line art or black and white .jpg) and in most cases they must be converted and dithered, or use photograv, to render your greyscale files. If your using photograv you must use bmp's which are considerably larger than .tif and converting from a saved .jpg to a bmp eliminates any storage memory savings you gain by using the substandard format.. .jpgs should only be used where they belong, on the web..

Rodne Gold
01-26-2007, 2:05 PM
I do digital photography with a DSLR , a lot of it , I also do digital large format printing and many other forms of printing , so I talk from many years experience here.

DPI is a rubbish concept , its the output that a device is capable of and one dot of that device does not map a pixel when it comes to anything being printed barring a 1 bit image or a printer like a dye sub that can map a pixel to a dot.

Regardless of what your software says , the only thing that counts is pixels , how many of them there are will determine how good a thing will print and its resolution , not dpi.

JPEG is not a bad format at all and they are not merely "web files" , go to any photography forum where the printing requirements are far greater than any laser can possbily output and see what formats are used to print and for that matter to take pictures , ALL cameras right up to the top of the range pro models use JPEG to capture and store (and some use raw files) and those files print just beautifully and are accepted by just about any bureau that prints. a Tiff or uncompressed file can be MANY times the size of a jpeg , go load a 7 meg jpeg vs a 70 mb Tiff into any editing program and see what your processing overhead will be.

I dont get your greysale and fuzz and black and white thing.
The laser can only engrave black or white (no engraving) so it uses halftones (spaced clusters of black and white) to simulate shades of grey , the way that halftones are generated is either in a driver or software - the fact photgrav works with a bmp is part of Photogravs archaic programming not cos you can only generate a decent 1/2tone from a BMP. You can print a greyscale JPEG very well on a laser printer , a laser is exactly the same as a black and white laser printer. Photograv does not generate halftones per se anyway , it generates a 1 bit black and white image from a halftone image and generates this with miore than just a DPI figure in mind , it compensates for heat affected zones , spot size and the resolution the material can hold , it's so called "halftone" image is VERY gross anyway , it does SERIOUS sharpening which basically destroys detail , it would not be acceptable in terms of anything but the poorest printer , so even if you use an ultra compressed jpeg , it would not matter. Obviously if you used ANY low resolution image in any format (like a 80 x 80 pixel image printed 4" x 4") you will get a very pixelated result.
This JPEG is bad thing and should never be used is just misinformation or misunderstanding of the format. There are times it shouldnt be used , sucha as saving very low resolution images in the first place as the jpeg artefacts will do em no favours.
Do some more research on JPEGS , you are not correct in damning them as substandard , they ARE the standard for many high end printing applications and are a very useful format , same as MP3's , you get bad jpegs if you try compress to hell and gone with the worst quality selected.

Bill Cunningham
01-26-2007, 3:42 PM
I do digital photography with a DSLR , a lot of it , I also do digital large format printing and many other forms of printing , so I talk from many years experience here.

I've been in the printing business for 18 years

DPI is a rubbish concept , its the output that a device is capable of and one dot of that device does not map a pixel when it comes to anything being printed barring a 1 bit image or a printer like a dye sub that can map a pixel to a dot.

Regardless of what your software says , the only thing that counts is pixels , how many of them there are will determine how good a thing will print and its resolution , not dpi.

When the 'software' gives you no choice what choice do you have?
A person will relate to what they see, and what their software 'gives' them to see.. Corel uses DPI, laser engravers use Corel..PPI relates to your screen, DPI relates to your output..

JPEG is not a bad format at all and they are not merely "web files" , go to any photography forum where the printing requirements are far greater than any laser can possbily output and see what formats are used to print and for that matter to take pictures , ALL cameras right up to the top of the range pro models use JPEG to capture and store (and some use raw files) and those files print just beautifully and are accepted by just about any bureau that prints.

Not by any company the prints Quality.. No trade printer I have ever delt with will accept and rip a .jpg without telling you about the loss in quality you are going to receive.. With BIG prints, High Quality printing does not matter, because in most cases the eye is to far away to see the pixelated image.. The bigger the picture i.e. large format, and billboard size requires very little resolution, and yup a .jpg is good enuff..

I dont get your greysale and fuzz and black and white thing.

Obviously.. There is no such thing as a black and white .jpg.. So if you take a good look at the edges of the image, it will be pixilated to one degree or the other.. The crappier the .jpg, the more pixelated the edges will be, and the more fuzz on the output.. The edges of a .jpg do not go from black to white as a binary image would. It goes from black to grey to white, and the grey is 'fuzz'

The laser can only engrave black or white (no engraving) so it uses halftones (spaced clusters of black and white) to simulate shades of grey ,
The Grey is the fuzz at the edges of the .jpg

the way that halftones are generated is either in a driver or software - the fact photgrav works with a bmp is part of Photogravs archaic programming not cos you can only generate a decent 1/2tone from a BMP.

I never said that, I was only comparing final output sizes

You can print a greyscale JPEG very well on a laser printer , a laser is exactly the same as a black and white laser printer. Photograv does not generate halftones per se anyway ,

I Didn't say that.. I said you could 'convert' by dithering or use photograv.. I assumed that any one using photograv would know that it does not create halftones, only simulates by dithering and enhancing edges..

it generates a 1 bit black and white image from a halftone image and generates this with miore than just a DPI figure in mind , it compensates for heat affected zones , spot size and the resolution the material can hold , it's so called "halftone" image is VERY gross anyway , it does SERIOUS sharpening which basically destroys detial , it would not be acceptable in terms of anything but the poorest printer ,
Again, were engraving, not printing

so even if you use an ultra compressed jpeg , it would not matter. Obviously if you used ANY low resolution image in any format

But 'why' lean towards the lowest quality file, just because you can use it?

(like a 80 x 80 pixel image printed 4" x 4") you will get a very pixelated result.

This JPEG is bad thing and should never be used is just misinformation or misunderstanding of the format.


Do some more research on JPEGS , you are not correct in damning them as substandard , they ARE the standard for many high end printing applications.

Most (virtually all) of the printing I have been involved with is high end 4 colour work .. Jpgs may be fine for BIG stuff seen at a distance but NOT for any high end printing I have been involved with for the last two decades.. I agree that the laser is not capable of reaching the output quality of even mediocre files, but .jpgs are desktop publishing stuff and not for 'quality' work. They are simply a derivative of the new digital world, (I still think film is better, but hey , you have to go with the flow:() Jpg's are the bane of the publishing house.. Along with .doc files...I think anybody reading this thread, has a pretty clear idea of where we each stand, Lets just call this a difference of opinion, and end it here.. After two decades, I simply can't bring myself to use, or accept them in the printing industry, so inturn, I have a difficult time accepting them for 'any' output that is not on a video screen.. Call me old fashioned..:D

Frank Corker
01-26-2007, 7:04 PM
Bill, Rodne

Guys, your words of wisdom are something none of us ignore, you both have very valid points and I am sure that even those amongst the members here have learened a lot and will continue to learn from it.

DPI and PPI are confusing for the 'average joe'. How about giving us a write up on how you prepare your jpg pictures for lasering (detailed - includes the means of finding out what dpi ppi your picture is when you get it or how we go about achieving it). Without any doubt in my mind this would be a MASSIVE help to everyone.

Another thing, whilst on the subject of getting your picture to the laser, I also notice that some are not taking to Photograv (because of it's much needed upgrade) the other methods you/ve can use to prepare it. Again step by step will most certainly help.

I'm sure I have actually said what a lot of the members are actually wanting to hear, if I am wrong I can only apologise, but a clear prescise post would make an excellent pointing post for everyone to refer to. You all know as well as I that this question is going to pop up in a couple of months when the next person who becomes a member and/or purchases their laser engraving machine.


:)

Rodne Gold
01-26-2007, 11:18 PM
I actually posted the step by step to get to a photograv output , here is is again.

Here's how to do it In photoshop

1) Convert to 8 bit greyscale (image/mode/greyscale)

2) Resize the image to the size its gonna get engraved using 150-300 ppi (150 for less detail)
(image/image size)

3) Bump up contrast and brightness about +25 in
both cases - you dont want the pic to be insipid areas of medium grey. (image/adjusyments/brightess-contrast)

4) Heres the VITAL part - use unsharp mask at 500% and a radius of 3-5 pixels - threshold 0 - this will exaggerate edges radically , but thats what you need. In fact you can do this and then STILL add another unsharp mask at 150 % , 1pixel and 0 threshold AFTER the 1st unsharp if you want even more edge detection
(filter/sharpuen/unsharp mask)

5) Convert to a bitmap using 125-150ppi and a diffusion pattern. (image/mode/bitmap)

5) laser.

that will give you essentially similar or better results.

As to DPI and PPI , that is simple.
Essentially , you need to know your image size in pixels , you can ignore dpi

DPI is merely a measure of the capability of an output device , IE a screen can only display lets say 100 dots for 1 inch of real estate and a black and white laser can only output 600 dots per inch.

However this is not really relevant in terms of images as they are NOT measured in dots per inch but in pixels. a pixel is a single element that has brightness and colour info in it.
In a simple case , a 100 x 100 pixel image will display at 1" x 1" on a 100 dpi device that can map a dot to a pixel , if the laser could map a dot to a pixel , then it would print 1/6th of an inch by 1/6th of an inch on a 600 dpi laser.
BUT , printers cannot generally map a pixel to a colour cos they cant print unlimited colours/shades. A colour pixel can be one of millions of colours , a colour inkjet printer with CMYK colours can only print 8 colours , C, M, Y , K , C+M, M+Y, C+Y and white (no print).
So what it has to do is fool the eye it can accurately represent the pixel its printing and it does that by printing a matrix of printed dots with various overlaps and spacing.
With a laser , the laser is capable of only printing ONE colour - black!
However we are asking the laser or laser printer to print grey?? It can only do that by using cells of its dots to represent grey pixels.

For example lets say it uses a 3 x 3 matrix of dots to "fool" us , white would be no dots printed in that cell , black would be all dots printed in that cell , the lightest grey would be one dot printed etc.
So its obvious now that the DPI (DOTS per inch) is not at ALL equal to pixels per inch , as the amount of pixels an inch the output device can print is depedant on how it uses its cells of dots.
Now a laser engraver is only a 300 discrete Dot per inch output device despite what the laser drivers say.
You can work it out real easy , the smallest spot size you can get using our lasers is 0.003" , you can only get 300 of those spots into an inch without them overlapping
If the laser wants to represent only 8 shades of grey , it would need a 3 dot by 3 dot matrix.
so if you want your laser to print 8 shades of grey , all the laser can resolve is a 100 pixel per inch greyscale image.

There is nothing stopping you presenting the laser a higher pixel per inch image , in fact , due to nyquist theorum (which im not going to get into) it SHOULD be 2x the theoretical to get best quality

By going overboard here , you increase processing time and if the image resolution is too high , waste processing time and introduce innacuracies when the software has to sample downwards.
There is a REAL simple formula you can apply to images to be lasered . for perfect output , Make sure you have 150-200 Pixels per inch of image at the size you are going to engrave - end of story!!
You want to engrave a 4" x 6" image , DPI means absolutely NOTHING - you need a 600/800 pixel by 900/1200 pixel image - thats it!!
Size matters not dpi.

Rodne Gold
01-26-2007, 11:26 PM
Bill , Im not going to take this further , the whole world and any printer that knows their oats will accept a high resolution jpeg and print it beautifully for any application.

Dave Jones
01-27-2007, 12:42 PM
Rodney, I agree with a lot of what you are saying, but there is one fundamental thing that is not correct with your explanation.

Diffusion dithering and noise dithering (Photograv uses an adjustable blend of those two in interactive mode) is not cell based. Halftones are, but dithered images are not halftones and are not cell based. They are a much more complex conversion method that uses dot density to simulate the shades of gray. But that dot density is not based on evenly spaced cells of n x n dots.

While it is not capable of converting every pixel to a shade of gray at full resolution, it is capable of conveying much higher resolution than a halftone because it can place dots along sharp transitions of gray at close to, or even at, the full resolution of the output device rather than only at the lower resolution of a fixed grid like a halftone. Dithering won't resolve every pixel. It can't show low contrast details in an image at any higher resolution than the halftone. But since it is not grid/cell based, it can resolve far higher detail on edges within the image and therefore can show an image at much higher resolution than a halftone.

Dithers can also simulate many more shades of gray in areas of the image that are large sections of gray or gradients than halftones can, since it is not limited to a certain number of dots within a cell.

Because it is a blend of lower resolution dot patterns and some higher resolution edges, it is much harder to quantify a maximum useful resolution with a dither conversion. The user will have to decide for themselves if it's worth longer precessing times to do the conversion, but with today's computers that conversion time is virtually instant. There is no difference in lasering time when sending a 300ppi image converted to a 300dpi dither versus a 100ppi image converted to a 300dpi halftone. But there is a large difference in the quality of the final print. There is also no difference in laser time when sending a 100ppi image converted to a 300dpi dither and a 300ppi image converted to a 300dpi dither.

Just like the fact that JPEG is a very efficient compression scheme for photos because it takes into account the way the eye sees photographs, dithering is a more accurate way of rendering images to dots because it can convert edge transitions at higher resolutions and can convert low resolution areas to more shades of gray.

Rodne Gold
01-27-2007, 12:54 PM
Dave , yeh , I was trying to keep it real simple on a theoretical basis that a "layman" can visualize to illustrate the relationship between ppi and dpi.

In theory , due to Nyquist , the best you will ever get is if you use 2x as a sampling frequency , thus if your media and printer is able to resolve 150ppi and no more , then 300 ppi is the most you should ever ever use , anything more is simply a waste.
There are so many variables in terms of lasering a pic , that there can be no one size fits all strategy.

Dave Jones
01-27-2007, 2:55 PM
There are so many variables in terms of lasering a pic , that there can be no one size fits all strategy.

Absolutely true. And the differences between many methods can be so subtle that a lot of people would never notice the difference.

Brian Robison
01-30-2007, 11:11 AM
Thanks for the information. I didn't mean to start an argument. ;)
Rodne, I don't use PhotoShop. I was hoping to do everything in Corel. I don't use PhotoGav either.
I have redrawn the photo in CorelTrace. This has allowed me to manipulate the drawing. I'm concentrating on sharpening up the lines and fonts, deleting some of the shades entirely. So far so good. This "photo" has too much greyscale and not enough contrast IMO.

Dave Jones
01-30-2007, 1:21 PM
Chances are that you can use Corel PhotoPaint to do all the steps that Rodney outlined for Photoshop. The names of some things might be different, but I suspect the program has similar filters and conversion abilities.

Bill Cunningham
01-30-2007, 10:33 PM
Yup Corel photopaint has all the same controls Rodne mentioned.. At least from 11 on.. I know years back, using corel 8 you 'could' do it, but there is no choice in dither types and good results were more difficult to obtain.. The advantage I found with photograv, was speed.. Once you fiddled around with the parameters and improved the result for your machine (and saved them), you only had to push a button to get acceptable results on a repeat of the same material.. A minute saved, is a dollar earned ;)