Print issue ?

[Recrem]

Hi 

I have recently scaled up an image produced with Gimp to print 83 x 50cm. I generally produce the image at 50 x 30cm but had a special request for a larger image. 
I've printed at the smaller size and never noticed any problem.. haven't had any similar problem in ten years of producing and printing images. 

I was surprised to find the printed image was larger on the left side than on the right by 3mm. 

I went back and checked the digital image thinking the image must have been distorted by the "unified transform tool" and left short on the right side.. but found on checking that the image completely filled the 83 x 50 rectangle with no visible empty background ? 

We have since printed the same image twice and it is still 3mm short on the right side. 

I am not certain if this problem has originated in Gimp or via the printer software.. I sent the image to a printer as a jpeg and they checked it in PS before printing.  
Are there any known issues with certain printers.. or image file formats ? 

Has anyone encountered this issue before ?

And if they did how did they resolve it ? 

Thanks in anticipation.

[rich2005]

A reminder that Gimp works in pixels not centimetres, however

Could do with a little more information - pixel size / ppi of the original image before scaling.

One immediate question. Why use the Unified transform scale rather than Image -> Scale Image which must be a more accurate way.

First thoughts, There are rounding errors - pixels to real-world-units. 30 cm x 50 cm which might be so close as to make no difference but scaled up to "50 x 80" gives an actual 50 x 83.3  which would be that 3 mm.

   

Have you checked the original for a tiny error that might be magnified by scaling.

If stuck maybe scale oversize by a tiny amount and crop back down to size.

[Ofnuts]

I don't see how this can happen from the Gimp side unless you did a bit of perspective correction and didnt't notice a tiny transparent band along one of the edges.

Otherwise everyhing is possible, including a slight paper feed problem in the printer. If the edges of the rectangle image are clearly identifiable, are they all exactly perpendicular to the paper edges?

I would print a grid image to see if the problem is progressive over the whole picture or if distortion starts past a given point.

[Recrem]

(05-25-2019, 08:38 PM)Ofnuts Wrote: > I don't see how this can happen from the Gimp side unless you did a bit of perspective correction and didnt't notice a tiny transparent band along one of the edges.

I checked the original image and there was no transparent band.

> Otherwise everyhing is possible, including a slight paper feed problem in the printer. If the edges of the rectangle image are clearly identifiable, are they all exactly perpendicular to the paper edges?

> I would print a grid image to see if the problem is progressive over the whole picture or if distortion starts past a given point.

I'll try that. 

[Recrem]

Ok here are various screen shots of the two images. 

1 is the original image before upscaling.  
2-3-4 are the upscaled image used to print



Notice the image fills the bottom right corner as it does on the print image

2. 

Above is the scaled printed image showing the bottom left corner. 

3. 



The image above shows the top right of the upscaled image used for printing. 

4. 



Show the top right of the printed image. 

Basically all four corners are filled to the end of the rectangle.

In response to Rich2005 I mentioned the "unified transform tool" because I believed it might be possible that the printer had used it on the image..and that I myself might have made slight adjustments using it.  

We've printed 3 times using the second print file and on each occasion it is 3mm short on the left side.

[rich2005]

Somehow you have different aspect ratios. Remember Gimp uses pixels so:

original image 5944 / 3566 = 1.6668

scaled image 9803 / 5906 = 1.6598

For scaling even using cm as units I advise letting Gimp do the arithmetic. With the width and height linked together

Using Scale Image : Enter 50 in the Height box, Click in the Width box and the size in pixels is determined. 9844 x 5906 pix.

   

9844 - 9803 = 41 pix difference = 41 / 300 ppi = 0.1366 inch = 3.47 mm

[Recrem]

(05-28-2019, 07:49 AM)rich2005 Wrote: > Somehow you have different aspect ratios. Remember Gimp uses pixels so:

Hi Rich 

Originally the client asked for a specific size which would have increased the height but not the width and I explained would distort the appearance.  

After exchanging a series of emails we settled on 83cm x 50cm. So the print size came from the discussion with the client. 

Would that cause the printed image to distort only on the right side leaving it 3mm short ? 

Could you outline what you would do to achieve successful upscale to achieve a printed image as near as possible to 83 x 50 ?

Thanks for your feedback.

[rich2005]

Quote:..Would that cause the printed image to distort only on the right side leaving it 3mm short ?

Not a distortion. You already have it as close to 83 cm x 50 cm as possible The problem is not keeping the same aspect ratio as the original.

Getting  calculator out.

83 cm / 2.54 = 32.67716  inch  32.67716 x 300 ppi = 9803 pixels Edit: If that prints at 827mm wide then there is a problem with the printer.

50 cm / 2.54 = 19.68504 inch  19.68504 x 300 ppi = 5905 pixels

If you want the missing 3 mm on the margin then the size needs to be 9844 x 5906 pix.

Just to throw a spanner in the works  Are you sure you need to use 300 ppi? What is the printing process? Colour photo laser printers typically use 100 pix-per-cm (254 ppi and produce superb results with interpolation).  Even with an inkjet 80 x 50 cm is a large print Does it need 300 ppi ? - ask your printer.

[Recrem]

(05-28-2019, 09:17 AM)rich2005 Wrote:

Quote:..Would that cause the printed image to distort only on the right side leaving it 3mm short ?

Not a distortion. You already have it as close to 83 cm x 50 cm as possible The problem is not keeping the same aspect ratio as the original.

Getting  calculator out.

83 cm / 2.54 = 32.67716  inch  32.67716 x 300 ppi = 9803 pixels Edit: If that prints at 827mm wide then there is a problem with the printer.

50 cm / 2.54 = 19.68504 inch  19.68504 x 300 ppi = 5905 pixels

If you want the missing 3 mm on the margin then the size needs to be 9844 x 5906 pix.

Just to throw a spanner in the works  Are you sure you need to use 300 ppi? What is the printing process? Colour photo laser printers typically use 100 pix-per-cm (254 ppi and produce superb results with interpolation).  Even with an inkjet 80 x 50 cm is a large print Does it need 300 ppi ? - ask your printer.

- - - - - 

Would you say this is "a" possible cause or "the" cause ? 

I understand what you are saying.. but I am not clear why that would make the image shorter on the right than on the left ? 

If there are other possible causes I'd certainly like to hear them. I'd like to work through a series of options (if there are any other options) and then print rather than print and find it doesn't resolve it.

[rich2005]

Hopefully you will get more answers. First thing I would do with what you have already printed is determine if the print is actually 830 mm wide. 
Then if an inkjet printer does it impose a 'feed' margin at the end of the print. Is the printer scaling the image 'to-fit'. All unknowns here.

I once had a Canon inkjet that would not print panoramas. Got up to 40 cm on roll paper and stopped there Truncated the image.