Cool. I'm exploring that way. If anyone has experience with this, I'd also be happy to try their suggestions :)

Thanks again !

Thanks!

Although I want to eventually use more personal effects, this is why I want to start with a simple b&w shader... :)

The photos.save_image trick is great to know btw.

Hello,

I'm quite new here, and hope this topic hasn't been beaten to death (I looked a bit and it doesn't seem so, so here we go).

I'd like to make a simple script that take a picture with the camera (or picks one from the roll), apply a simple shader (GLSL), which basically turn the image B&W, and then save it to the iOS roll.

The example I found (filters.fsh in the games directory, and Simplexnoise) was meant to apply the effects in real time. The document scaning script seems to be closer to what I want, but instead of the enhance_contrast() function using CIFilter, I'd like to use a similar function with a custom shader.

How should I go about doing this? Here's my code so far:

Shader (bwShader.fsh) :

varying vec2 v_tex_coord;
uniform sampler2D u_texture;
uniform float u_scale;
uniform vec2 u_sprite_size;
uniform float u_time;

vec4 grayscale() {
	vec4 color = texture2D(u_texture, v_tex_coord);
	float contrast = 1.7;
	color = (color - 0.5) * contrast + 0.5;
	float gray = (color.r + color.g + color.b) / 3.0;
	return vec4(gray, gray, gray, color.a);
}

void main() {
	gl_FragColor = grayscale();
}

Python script, adapted from the scaning example :

import photos
import console
from objc_util import *
from scene import *

CIFilter, CIImage, CIContext, CIDetector, CIVector = map(ObjCClass, ['CIFilter', 'CIImage', 'CIContext', 'CIDetector', 'CIVector'])

def take_photo(filename='.temp.jpg'):
	img = photos.capture_image()
	if img:
		img.save(filename)
		return filename

def pick_photo(filename='.temp.jpg'):
	img = photos.pick_image()
	if img:
		img.save(filename)
		return filename

def load_ci_image(img_filename):
	data = NSData.dataWithContentsOfFile_(img_filename)
	if not data:
		raise IOError('Could not read file')
	ci_img = CIImage.imageWithData_(data)
	return ci_img

def enhance_contrast(ci_img):
	filter = CIFilter.filterWithName_('CIColorControls')
	filter.setDefaults()
	filter.setValue_forKey_(2.0, 'inputContrast')
	filter.setValue_forKey_(0.0, 'inputSaturation')
	filter.setValue_forKey_(ci_img, 'inputImage')
	ci_img = filter.valueForKey_('outputImage')
	filter = CIFilter.filterWithName_('CIHighlightShadowAdjust')
	filter.setDefaults()
	filter.setValue_forKey_(1.0, 'inputShadowAmount')
	filter.setValue_forKey_(1.0, 'inputHighlightAmount')
	filter.setValue_forKey_(ci_img, 'inputImage')
	ci_img = filter.valueForKey_('outputImage')
	return ci_img

def bw(ci_img,shader):
        # PROBLEM HERE?
	ci_img.shader = shader
	return ci_img
	

def write_output(out_ci_img, filename='.output.jpg'):
	ctx = CIContext.contextWithOptions_(None)
	cg_img = ctx.createCGImage_fromRect_(out_ci_img, out_ci_img.extent())
	ui_img = UIImage.imageWithCGImage_(cg_img)
	c.CGImageRelease.argtypes = [c_void_p]
	c.CGImageRelease.restype = None
	c.CGImageRelease(cg_img)
	c.UIImageJPEGRepresentation.argtypes = [c_void_p, CGFloat]
	c.UIImageJPEGRepresentation.restype = c_void_p
	data = ObjCInstance(c.UIImageJPEGRepresentation(ui_img.ptr, 0.75))
	data.writeToFile_atomically_(filename, True)
	return filename

def main():
	
	with open('bwShader.fsh') as f:
		src = f.read()
		shader = Shader(src)
	
	console.clear()
	i = console.alert('Info', '...', 'Take Photo', 'Pick from Library')
	if i == 1:
		filename = take_photo()
	else:
		filename = pick_photo()
	if not filename:
		return
		
	ci_img = load_ci_image(filename)
	
	out_img = bw(ci_img,shader)
	#out_img = enhance_contrast(ci_img)
	
	out_file = write_output(out_img)
	console.show_image(out_file)
	print('Tap and hold the image to save it to your camera roll.')

if __name__ == '__main__':
	main()

Thanks a lot. Once again, I hope I'm not too far off (or too imprecise) with this question.