Clearification DPI verses Pixels:

[Robert Andersson]

I think it can be good to clear out the difference between pixels and dots per inch. This is used i IronCAD when images and animations are produced.

 

What is a imagefile?

It is a small database consisting of:

First a specifikation of itself saying witch file format (JPG,BMP,TIF) and version and more.

 

The image file then consist of the image data formed as a number of columns and a number of rows.

An image with the resolution of 640 x 400 pixels have 640 bytes (computer words) in X directions and 400 in Y direction.

Each byte have a value. That value is a specific color stored in hexadecimal form.

 

Then the imagefile also have something called DPI value. It is a simple numerical string stating hove big the image should be when printed.

Thats about all a image consist of.

The DPI value does NOT affect the image file size. Only pixels affect filesize.

Images editors can change the DPI value up or down without lossing any quallity at anytime.

DPI value are not interesting when exporting animations in IronCAD. Only pixelvalues are of interest.

 

So hove does pixels/ dots work togheter?

 

1. I want to have the best possible image quality to view on my PC screen:

Export the image with the same X and Y pixels as your PC screen can show. Normaly 1280x 1024 pixels.

I now assume that you look at the image in fullscreen.

DPI are without effect here. More pixels will not add to on sceen quality.

 

2.Best quality for printing?

This is more complicated.

When it comes to printing you have to be familiar with the printers tech specifications.

First check what resolution the printer can create on paper. This is mesured in dots per inch. That is ink dots for a inkprinter.

Say you have a printer that can produce 600 dots per inch. (That is in X)

First you have to chose hove big your image should be on the printed paper. Say it should be 3 inches wide.

Then use this formula:

3 inch x 600 dots per inch gives 1800 dots totally needed.

Then you should export an image from IronCAD with this data:

Pixels: 1800x1350

Dots/ inch=600

That image will be 3 inches wide on paper.

If you export the image with the same pixels but with the Dots value set to 300 dots per inch, the image will be twice as wide on paper.

What if I export a image with 1000 DPI?

-It will not add to printed quality in this casecause the printer cant handle more than 600 dots per inch. The image will be smaller do.

So the DPI value just says to the printer over wich area the pixles should be stretched.

If you need to adjust the printed image size in your desktop publishing software, change the DPI value, not the number of pixels.

 

Robert Andersson

Solidmakarna

[tlehnhaeuser]

Hi Robert,

Does this prinicpal apply to getting realistic textures on parts in the Scene? For instance a client wants to have a pre-cast concrete texture to a part. But we find an image we want, but it changes when applied to the part. We try to change the settings to "increase" the number of "bubble holes" on th concrete but scales the image with proportionately. ultimately want to increase the size of the image without scaling the "holes".

 

they only way is to create the texture in an editor to the exact size then apply to part. But how do we determine what the right size, dpi, pixel etc..is required for optimal realism? That is the question.

 

any feedback is welcomed.

Tom

 

 

Tom Lehn...

Magnacad Design Inc.

http://www.magnacad.com

[Mike Allen]

It may help to create a "tiling" image for mapping. This is an image in which the top edge matches the bottom edge and the right edge matches the left edge. The main trick is starting with an image that is lit evenly (no shadows.) Then open the image in PhotoShop and apply the Offset filter (Filter>Other>Offset...) to offset the image by half its height & half its width. Now you can use the Clone Stamp tool to paint over the edges, resulting in an image that can be tiled in a texture map (which would give you the appearance of a larger image without scaling the size of the holes.) This is all much easier said than done - make sure that your initial image doesn't have any shadows & you're halfway there.