Create High Resolution Bitmaps

Hello Everyone,
I am very new to image editing and I find it hard to get more information for my problem, since its very specific.

Lets start at the beginning:

I am using a label printer form a company, which requires me to use .bmp files with a 24-bit format to print out a set of pictograms on the label. The image containing the pictograms is roughly 5x14 mm in size. As of right now, they have a very bad image quality and I was tasked with increasing said quality. Seemed pretty easy to me at first: I got the high resolution pictograms from a colleague, arranged them in the way I need them and then set the image size and resolution in Gimp. This worked as intended, I have a high quality image containing the required pictograms in the correct locations.

My problem can be described as follows:
when I export the file (which is needed since I can’t use the natural .xcf file that Gimp creates) the physical size of the image increases beyond the 5x14 mm I need.

Additional information:
when I try to print the .xcf file, the image on the paper has the correct size, when I export it as a .bmp file and open that using any other programm, the physical size increases far beyond the size I need.

I know I am a total noob and I would really appreaciate if someone far more advanced in this type of stuff would be able to help me.

Thank you very much and have a lovely day!

You can scale your image before exporting it. I would make a copy and scale the copy, so as not to lose your high resolution version. The command is “Scale Image” in the “Image” menu. You can choose the units you want to use. I do this all the time, either with GIMP or with ImageMagick’s ‘convert’ or ‘mogrify’ commands.

Hello LaurenceFinston,

That’s exactly what I am doing. I am scaling the image to the size and resolution I want it to have, and then export it as a .bmp file.

When I open the .bmp file with Gimp again, it has the correct size. When I open it with another program, for example the windows photo viewer, then the image is far bigger. The same happens on the Label printer, the image is far bigger than I need it to be.

I don’t understand exactly what you mean. If you’ve scaled the image in GIMP and exported it, then it should have the correct size. In a program for viewing graphics, it might be displayed at a different size but that doesn’t affect the size of the image.

I would check that the image really has the correct size and/or that you’re really displaying the right image.

In GIMP, you can find out the size of an image with the “Image Properties” command in the “Images” menu. With ImageMagick, you can use the ‘identify’ command, e.g.:

identify glyph_dots_110.png

glyph_dots_110.png PNG 1726x982 1726x982+0+0 8-bit sRGB 78333B 0.000u 0:00.000

1726x982 is the width and height of the image (in pixels) and 1726x982+0+0 is the width and height of the page. Sometimes when I’ve made changes to images, the page width and height remain the way they were before. I don’t quite understand why this happens or under what circumstances, but it hasn’t made any difference with the way I’ve been using them. This might not be the case if images are used in other ways.

I’ll try to explain it in a more detailed way:

I have my image, set the size using Scale Image, and then save and export it as a 24-bit Bitmap. When I open that same .bmp in Gimp again, it still has the same size. Not only displayed in the UI, but also when I try to print it on a normal printer on paper.

Now when I open that same .bmp file with a different image viewer, like Paint, or Windows Image Viewer, it doesn’t only seem bigger in der UI, but also in the print preview. When I print it on the same printer I used before, the size increases. The same thing happens to my label printer.

I can rule out, that I am printing different files, since that was one of the first things I checked.

I really appreciate your help, and on Monday when I am back at work I will try to do the things you suggested and see if I can provide you with more information.

Thanks in advance!

I can only speculate as to why this is happening. Possibly scaling the image isn’t changing the page size and the software that prepares the document for the printer is using the page size. Is there a dialogue for scaling the document before it goes to the printer?

I don’t normally have files in bmp format. I usually have graphics in one of the formats Encapsulated PostScript, JPEG or PNG. If I want to print something, I use TeX and DVIPS with EPS most often, but occasionally pdfTeX with PNG. I think it also works with JPEG, but I’m not completely sure. Either way, it’s ultimately converted to PostScript. With TeX and DVIPS and pdfTeX, it’s possible to scale images to whatever size you want. I don’t know if that would be possible for your application, but if so, I would be happy to explain the procedure in detail, if you wanted to try this.

Welcome to GIMP, Julen.

I don’t think I can solve your problem, but maybe I can give you concepts and terminology which will help you think about it.

The number of mm which an image occupies on paper when printed is a function of two things:

  1. The “image size”, which is the number of pixels in the image, made up of the “width” — the number of columns of pixels — and the “height” — the number of rows of pixels.
  2. The “resolution”, which is the number of pixels per unit of distance (mm, inch, etc). There is an “X resolution”, the number of columns of pixels per horizontal distance, and a “Y resolution”, the number of rows of pixesl per vertical distance. The X and Y resolutions are often the same, but don’t have to be.

For more on this terminology, read 6.21. Scale Image in the GIMP documentation.

Does the label printer respect X and Y resolution values which the image file might contain? If it does not, then it probably interprets the image it reads as having an assumed resolution, such as 96 pixels per inch (dpi). I that case, the only way to get the label to come out as 5x14mm in physical dimensions is to give the printer an image which has the specific number of pixels which comes out to the correct physical dimensions at the printer’s assumed resolution.

Note that the printer probably has a fixed physical resolution for its printing mechanism: it always prints 200 pixels per inch, or 300, or some number. The printer’s software must necessarily convert any image which it reads into the printer’s physical resolution somehow. Maybe it is clever about it, like GIMP’s Scale image feature is. Maybe it is crude.

Some image formats have ways of storing desired X and Y resolution values in the image file, and some don’t. You need to find out whether the BMP format can store resolution values. If the BMP format cannot store X and Y resolution values, there is no way the printer could respect your desired X and Y resolutions. If the format can store resolution values, it may still be that a given label printer or application ignores those values.

You say that the current image has “bad image quality”. It sounds like your approach to improving quality is to increase the image size, that is, to put more pixels into the image, and have each pixel occupy less physical space. If that works, great. But if it does not, the alternative is to make an image with the number of pixels required to print the correct physical dimensions, then to edit the colour of individual pixels to make each pixel give the best contribution it can to the overall quality of the image.

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