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 Post subject: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 10:34 am  (#1) 
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Hi guys, me again!

For those who were following my previous post, SUCCESS!! :hi5 :bigthup :jumpclap :tyspin
I'll now be able to move forward on my RC project (even if my vacation time is up :( ). I now was wondering if there is a tutorial/way to:
1)cut/paste the tire sticker in this jpeg(3000x2252px@300dpi), rescale it to fit my RC tire (as shown),
Image
Image

2)or, can I use my original tire logo (from my decal project), and 'curve/bend' it to the RC tire dimensions?

Any ideas? I've been looking in the tuts section, found Molly's tut on text wrapping to an arc, but still searching....
Thanks guys!
Cheers!
S
:)


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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 11:12 am  (#2) 
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You will certainly bend it with the Distorts -> Curve Bend filter, but it is not a wonderful tool to use.

In this instance you might consider using Inkscape to vectorise the image. Bend it around a template. Export as a png at whatever size you want.

example http://i.imgur.com/YVSYj1x.jpg

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 11:32 am  (#3) 
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rich2005 wrote:
You will certainly bend it with the Distorts -> Curve Bend filter, but it is not a wonderful tool to use.

In this instance you might consider using Inkscape to vectorise the image. Bend it around a template. Export as a png at whatever size you want.

example http://i.imgur.com/YVSYj1x.jpg


So, rich2005,
The tool is not effective? I will need to install Inkscape? I'm not familiar with this program. Will it be easy to use?
Thank-you for your time
Cheers!
S


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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 12:06 pm  (#4) 
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It has quite a hard learning curve in my opinion. It does very nice work though.

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 12:16 pm  (#5) 
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Yeah, there is a steep learning curve with Inkscape, so maybe better to stick to Gimp.

The problem with the curve-bend filter is it only acts horizontally and leaves the ends vertical, which does not look correct.

This is the logo from a search, quite a big image.
Give it an alpha channel, Increase the canvas size for some working room and apply a perspective transform just to the logo, to slope the ends.

like this: http://i.imgur.com/n8uoOgK.jpg

Then apply the curve-bend filter, looks like this. http://i.imgur.com/HAeXtdc.jpg

Gives a result like this: Image

All a bit hit-and-miss I am afraid to get the ends and curvature correct.

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 12:28 pm  (#6) 
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The true tool for this is Filter>Distorts>Polar Coordinates

Typically you set your logo along the top border of a square layer which is going to be about 6x wider (if you want the logo to be a 60° arc on the rim, since the whole layer width is mapped to 360°), and apply the filter on that. You may have to squeeze the logo horizontally first (about 3.14x, must be a coincidence:)) to compensate for the change in aspect ratio. The result may be a bit blurry:

Attachment:
Michelin-bent.png
Michelin-bent.png [ 32 KiB | Viewed 32425 times ]

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 12:36 pm  (#7) 
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:ninja by ofnuts (but I have more pretty pictures, and doughnuts :yes )

Here is a mini-tutorial on using the Polar Coordinates filter to map your image to a curve.
1. Open the image that is to be curved. I used the following Gimpchat banner.
Image
2. Open the target image. I used a doughnut (mmm, doughnuts) instead of a tire.
Image
3. Determine on your target image where you want the banner to appear. You don't need to paint the "ring"; I only did that for demonstration purposes.
Image
4. Take two measurements: the diameter of the entire ring and the thickness of its circumference.
Image
5. Go back to your banner image and open the "Image->Scale" dialog. Click on the chainlink button in order to fix the aspect ratio of the banner and then change the height of the image to be twice the thickness determined in step 4.
Image
6. Next open the "Image->Canvas Size" dialog and again click on the chainlink to maintain the aspect ratio. Enter the diameter that you measured in step 4 as the new height. Click on the "Center" button and then change the Y-offset value to zero. Your preview should show the banner centered at the top of the image.
Image
7. Perform a "Layer->Layer to Image Size".
8. Open the "Filters->Distorts->Polar Coordinates" dialog and use the following settings.
Image
9. Autocrop the layer and then copy it over to your target (doughnut) image. Use the Move Tool to place it in position.
Image

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Last edited by saulgoode on Sun Oct 26, 2014 3:39 am, edited 1 time in total.

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 12:45 pm  (#8) 
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not exactly sure what you're trying to accomplish but
here's what i tried using scale and shear tools.
first image, i selected ellipse then sheared selection to fit the perspective of wheel. Then sheared the image to straighten out the perspective of wheel and scale it to fit the hubcab image.
Image

second image, i selected the hubcab using ellipse select tool, then scaled and sheared it to fit the hubcab of the wheel image.
Image

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 1:23 pm  (#9) 
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rich2005 wrote:
Yeah, there is a steep learning curve with Inkscape, so maybe better to stick to Gimp.

The problem with the curve-bend filter is it only acts horizontally and leaves the ends vertical, which does not look correct.

This is the logo from a search, quite a big image.
Give it an alpha channel, Increase the canvas size for some working room and apply a perspective transform just to the logo, to slope the ends.

like this: http://i.imgur.com/n8uoOgK.jpg

Then apply the curve-bend filter, looks like this. http://i.imgur.com/HAeXtdc.jpg

Gives a result like this: [ Image ]

All a bit hit-and-miss I am afraid to get the ends and curvature correct.


That's exactly what I'm getting, warps out the image. However, the flat tire (the one half hidden) is the logo I'd like to use (just the Michelin rectangle).
Ofnuts, that's exactly the result I've been getting too, a little off the mark IMHO.
Saulgoode, will try to do it as you mentioned, keep posted,
trandoductin, what you did there was what I'm trying to figure out, as the hidden tire logo was what I'd like to use (lettering is larger than my other decal logos, looks better on the tire (as shown), just have to arrange the curvature a bit better.

Thanks for all your ideas!
S


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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 2:23 pm  (#10) 
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saulgoode,
Followed what you suggested, but for some reason, the arc does not fit the tire wall well (took the tire image, rescaled it to my actual RC tire size in mm), dunno if I'm doing it wrong, or missed something;

trandoductin,
As I mentioned, trying to 'cut out ' the actual rectangle logo from the tire image, but somehow unable to do this (once again, rescaled the original tire image to my RC tire size). This is where I'm stuck right now.
Will try to figure where I'm doing wrong.
Thanks guys!
S


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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 2:54 pm  (#11) 
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Sc00by5ting wrote:
saulgoode,
Followed what you suggested, but for some reason, the arc does not fit the tire wall well (took the tire image, rescaled it to my actual RC tire size in mm), dunno if I'm doing it wrong, or missed something;

Here's my result:


Attachments:
michelin.jpg
michelin.jpg [ 142.02 KiB | Viewed 3134 times ]

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 3:29 pm  (#12) 
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saulgoode wrote:
Sc00by5ting wrote:
saulgoode,
Followed what you suggested, but for some reason, the arc does not fit the tire wall well (took the tire image, rescaled it to my actual RC tire size in mm), dunno if I'm doing it wrong, or missed something;

Here's my result:


That is excellent! :bigthup But I was wondering if the original tire image could be 'cropped' out? (the flat-facing tire only)
Image
The lettering on the tire is much larger and more readable. I had opened a blank A4 w/transparency, pasted my rescaled original tire to the actual RC tire size (139mm dia.), and simply printed out a test sheet, and the decal came out perfectly! Can Gimp cut out this decal, so as to make multiple copies on a decal sheet?
Cheers!
S


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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Sun Aug 17, 2014 4:24 pm  (#13) 
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interesting,

found a michelin on the internet and enlarged the lettering larger like shown in the wheels picture.
Image
I tried using polar coordinates as described above.
here's my try.
Image
here's the logo before i pasted on the hubcab
Image

glad to have learned something new today (how to curve a banner using polar coordinates :))

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Mon Aug 18, 2014 5:12 pm  (#14) 
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trandoductin wrote:
interesting,(...) glad to have learned something new today (how to curve a banner using polar coordinates :))

Me too! :yesnod
Saulgoode thx for the tutorial! :tyspin

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Mon Aug 18, 2014 8:06 pm  (#15) 
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Saulgoode,
will try it over again, making sure all steps are followed precisely, and if you guys would like to know,
1)Actual RC tire outer diameter (for decal): 139.4mm (sorry, gotta use metric for me!) ;)
2)Actual RC tire thickness of circumference: 9.5mm

trandoductin;
you got it down good! the lettering is a lot more to what you would actually see on a real WRC rally car (thx youtube!)

I've got to go rest for my work tomorrow, but will try to work on it after work.
Stay tuned...
Cheers!
S


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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Tue Aug 19, 2014 7:08 pm  (#16) 
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ARRGH! :gaah
Saulgoode,
used my jpeg decal I used for my RC body (3541x621px@300dpi), followed your steps to the letter (with the measurements mentioned in previous update), and made a very blocky rendition of a decal that is only 1.5mm thick (!?!) I honestly do not know what I'm doing wrong, as I'm referencing the actual RC tire wall measurements.

trandoductin,
noticed you found a decal similar to mine, can you specify what the actual jpeg 'name' is (to see if it is the same as the one I found) I really want to succeed with this, and its frustrating when my result is nowhere near you guys. I'm learning this program as I try to achieve this project, so I'm light years behind. But I will persevere! Patience will reward me with a proper result!

Thanks again guys!
S


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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Tue Aug 19, 2014 7:21 pm  (#17) 
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If you want to speed things along, post an image of your decal and an image of your tire (side view, similar to the shot trandoductin and I used but without any decals).

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Wed Aug 20, 2014 3:17 am  (#18) 
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I followed the tutorial Saulgoode and got good results.
Below an example.
I used these images:
Tire - http://www.brazmax.com.br/painel/princi ... grande.jpg
Logo - http://www.asadelaloire.com/rallyegier1 ... chelin.jpg


Attachments:
pneuClogo.png
pneuClogo.png [ 611.14 KiB | Viewed 3026 times ]

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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Thu Aug 21, 2014 5:24 pm  (#19) 
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Update,
still getting shrunken logos (should I be translating to px, instead of mm?)
Anyhow,
here's the original tire pic
Image
(Actual tire diameter is 139.05mm, but the outer edge of tire wall is 129mm, inner edge of tire wall is 109.41mm)
Image
Actual file used for decal
Image
I really don't know what it is I'm doing wrong, but I will keep trying until I get it right, because your tutorial saulgoode seems bulletproof.
To be continued...
Thanks guys for your help!
S


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 Post subject: Re: Can an image be shaped to an arc?
PostPosted: Thu Aug 21, 2014 9:40 pm  (#20) 
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Here is the result I achieved using your images (I slightly cropped the decal to eliminate the white border around it):

Image

The XCF file can be downloaded from the following webpage:
http://barn.kerosenecow.net/u/saul/m/michelin-xcf-d7d2/

Before starting, I first scaled the tire image so that the tire was 139mm in diameter at 300 DPI.

I then created a selection around the outer circumference of the "whitewall" and noted it was 1526 pixels in diameter. I then created a selection around the inner circumference and measured the thickness of the "whitewall" to be 91 pixels.

I scaled the decal image to be 1103x182 pixels (actually I just changed the height, the width of 1103 was automatically calculated to maintain the same aspect ratio).

Next I resized the canvas of the decal to be 9198x1526 pixels (again, the width was automatically calculated by GIMP based on a height of 1526 and a constant aspect ratio).

Next, I added an alpha channel to the decal layer and performed a "Layer->Layer to Image Size".

I then performed the Polar Coordinates operation, using an offset angle of 180 and unchecking the Map From Top option.

Finally, I autocropped the layer (resulting in a layer that was 562x139px).

The resulting decal layer was copied to the tire image to verify that it fit.

If done properly, the decal layer should be able to be added to a letter-sized image and printed on a 300DPI printer.

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