White Border In Alpha Images

[killer-tomatoes]

Hi

I have one problem with the images that have Alpha. When I render the image the alpha work ok (make the object transparency) but Maya make one little white border (or small white edge) in the image.

IMAGE

The first image is the original image is PSD with a correct alpha the secon is the same image render with Maya. the white border is very significant in the legs of the table.

The problem is in all images with Alpha, and I test this with to much images and with lambert, blinn and phong materials, and render with Maya and Mental ray, but the withe borther is alwais in the render (all the time)...

The maya version is 2008... and this problem is from the version 6....

how can make clean alpha images renders????

[joojaa]

Its not a problem, its just a bit of information your missing.

Theres 2 equally smart ways to handle alpha pre multiplied and straight, gfx programs use straight alpha because its relatively easy to generate when you paint. however all real world based samplings produce alpha thats premultted alpha thsi includes photographs and 3d elements.

The advantage of premultted alpha is that you can view it without accounting for the alpha channel, while a straight allways needs tha alpha computed in.

the difference is:

rgb color * background separate alpha

rgbacolor * alpha + bacground

now because overlay is

rgb top + (1-Alpha)*rbg botttom for premultted

rbg top alpha +(1-Alpha) rbg botttom for unmulted

you actually save going back and forth.

the conversion between the 2 is relatively easy, in fact ps had a entire menu dedicated for this.

Now the problem is easily solved however i dont know which way around your going, if your going form ps to maya and back, you should save out straightened alpha (ps has the very counter intuitive way of dropping alpha to multed on save for formats such as iff or tif) To do this use image calcualtions to divide the bg contribution off and save the alpha as a separate channel and ditch it form the layer.

If your going the other way around ONLY, then just go to the matting menu and remove the matte thei unopremukts the image.

[killer-tomatoes]

Ok. The image is a PSD with transparent pixels (without specific alpha channel) I think that this is premultiply alpha. No?
This image go to lambert material in maya and I assign to one nurbs plane.

If I undestand you Joojaa I need premultiply the alpha channel with the RGB chanel in Maya.

I make this:

Hypershade

I connect the outColor of PSD node in the input1 of the node multiplyDivide
and outAlpha (1 channel) in the input2 (3 channel) of the node multiplyDivide and Multiply.
this make one RGB that I conect to the color of the lambert.
And finaly I connect the outTransparency to the transparency of the lambert.

This work better than only connect the color and transparency directly to the lambert but no is perfect, the small edge continues being there (to much small but is in the render)

help me please...?

[killer-tomatoes]

Hi..

I can't make perfect render with this... I put the project of maya and the image

Maya project

the project have two planes one with the image and one red for see the diference with the black.

and have two shaders:
mesa_original is the shader without touch
mesa_multiplicada that is the same with the multiplyDivide node.

Please help me....

[joojaa]

Your image has a slight matte problem (it becomes clearly visible once ou separate the color an alpha, its a trick i learnt form a master)! and its badly defringed at places. Theres also a serious miss in the left front corner.

you should never use psd files for anything except your i will always stay within photoshop work. Because the format internally is a bit iffy. (as its unmulted perfectly sanely but the choice of white as transparent is a bad choice on interpolating like 3d does it leaves a vital clue unused)

you cant do it with the network ps prettymuch ensures that with ist wierd use of trasparent.
See the biggest problem theres no such thing as transparent! just 4 colors

Heres a fixed and zipped image.

Escritorio.zip

(its essentially channel calculation operations, copy paste and delete, please note as you can see i can undo the image crapping you did in the middle without loss of much info, in fact no info is lost )

i played with the image bit but was far too layzy to fix all the matte pull problems

PS: Never ever send or open mb files form other users, use ma (as in ascii ot binary) files instead. theres HUGE security risk involved in a mb file thet quite frankly you shouldnt take EVER under any circumstances. Its lke telling the other part to give your computer over to him for free.

[killer-tomatoes]

Joojaa you are the BESTTTTTTT, you are the NUMBER ONE.

I have some years learn Maya, and some times I don't work 3d with maya for this (I'm work with Electric Image that don't have problems with PSD)

Thanks guy... ONE BEER FOR MY FRIEND!!!!!