Environment:
1. Windows Mobile 6
2. Vincent lib

1. I just created gradient image in vertical direction like the below:

int width=256; int height=256;
unsigned char data[256*256*4];
int x,y;
for(y=0;y<height;++y)
for(x=0;x<width;++x)
{
data[4*(x+y*width)] = y;
data[4*(x+y*width)+1] = y;
data[4*(x+y*width)+2] = 0;
data[4*(x+y*width)+3] = 255;
}
and then binded this texture like the below.
glBindTexture(GL_TEXTURE_2D, textureName);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);

2. I expected to be displayed gradiently but It shows like the step like the below.

Can you give me advices for this issue in OpenGL ES 1.x.
Is there any options list for me to ckeck?