I was just wondering: in general, what does "use of unresolved identifier mean"? I commonly get this and I am sometimes able to mess around until I solve it but there is never a consistent answer. So what is it telling me? 

Also, this piece of code keeps throwing that error and I am stuck! I'm sure it is super simple and I am just not seeing it! The error is on the "return newImage" line. Thank you for the help!

```
    class ColorBoost {

func turnRed(amount: Int) -> UIImage {
    for y in 0..<myRGBA.height {
        for x in 0..<myRGBA.width {
            let index = y * myRGBA.width + x
            var pixel = myRGBA.pixels[index]
            let redDiff = Int(pixel.red) - avgRed
            if (redDiff > 0)
            {
                pixel.red = UInt8( max(0,min(255,avgRed+redDiff*amount     ) ) )
                myRGBA.pixels[index] = pixel
            }
        }
    }

    let redFilteredImage = myRGBA.toUIImage()

    return redFilteredImage!

}

func turnBlue(amount: Int) -> UIImage {
    for y in 0..<myRGBA.height {
        for x in 0..<myRGBA.width {
            let index = y * myRGBA.width + x
            var pixel = myRGBA.pixels[index]
            let blueDiff = Int(pixel.blue) - avgBlue
            if (blueDiff > 0)
            {
                pixel.blue = UInt8( max(0,min(255,avgBlue+blueDiff*amount ) ) )
                myRGBA.pixels[index] = pixel
            }
        }
    }

    let blueFilteredImage = myRGBA.toUIImage()

    return blueFilteredImage!

    }

func turnGreen(amount: Int) -> UIImage {
    for y in 0..<myRGBA.height {
        for x in 0..<myRGBA.width {
            let index = y * myRGBA.width + x
            var pixel = myRGBA.pixels[index]
            let greenDiff = Int(pixel.green) - avgGreen
            if (greenDiff > 0)
            {
                pixel.green = UInt8(  max(0,min(255,avgGreen+greenDiff*amount ) ) )
                myRGBA.pixels[index] = pixel
            }
        }
    }

    let greenFilteredImage = myRGBA.toUIImage()

    return greenFilteredImage!

}

     }

      class chooseFilter {

func applyFilter(filterSelection: String) -> String {

    var callColor = ColorBoost()

    if (filterSelection == "coldImage")

    {
       var newImage = callColor.turnBlue(255); callColor.turnGreen(255)
    }

    if (filterSelection == "warmImage")

    {
        var newImage = callColor.turnRed(5); callColor.turnGreen(15)
    }

    if (filterSelection == "scaryImage")
    {
       var newImage = callColor.turnRed(-1); callColor.turnBlue(-1);   callColor.turnGreen(-1)
    }

    if (filterSelection == "mutedBlue")
    {
        var newImage = callColor.turnRed(-1); callColor.turnBlue(-1);   callColor.turnGreen(-1)
    }

    if (filterSelection == "green")
    {
        var newImage = callColor.turnGreen(2)
    }

 return newImage

```

the "return newImage" line is giving me the issue. (last line of the applyFilter function)

```
}

 }

 var filter = chooseFilter()
 var editedImage = filter.applyFilter("warmImage")

```