For example, I have a picture and its size is
900x600
and I want to put this picture into a box, which is 150x150 (different width/height ratio than the original picture)
What to do to generate a 150x150 picture from the original picture without distortion? (some picture contents can be cropped, it’s ok)
I made this crop function you could use. In example at bottom I’m using a red rect, just use display.newImage instead of the rect.
[lua]
local function crop(photo, newFileName)
– End size we want
local endWidth = 256
local endHeight = 256
local tempGroup = display.newGroup()
photo.x = display.contentCenterX
photo.y = display.contentCenterY
tempGroup:insert(photo)
– Find the bigger scale out of widht or height so it will fill in the crop
local scale = math.max(endWidth / photo.width, endHeight / photo.height)
photo:scale(scale, scale)
– This object will be used as screen capture boundaries object
local cropArea = display.newRect(display.contentCenterX, display.contentCenterY, endWidth, endHeight)
cropArea.x = display.contentCenterX
cropArea.y = display.contentCenterY
cropArea : setReferencePoint(display.CenterReferencePoint)
cropArea.alpha = 0.0
tempGroup:insert(cropArea)
– Now capture the crop area which the user image will be underneith
local myCaptureImage = display.captureBounds(cropArea.contentBounds)
display.save(myCaptureImage, newFileName)
--myCaptureImage:removeSelf() – Remove captured image
--myCaptureImage = nil
tempGroup:removeSelf()
tempGroup = nil
end
local photo = display.newRect(10,10,100,400)
photo:setFillColor(255,0,0)
– Put cropped photo into documents directory
crop(photo, “cropped.png”)
[/lua]
Joe, as per reply from @mpappas here http://forums.coronalabs.com/topic/38651-change-size-of-displaysave-image/
I think its a good idea to modify line 4 and 5 to:
[lua]
local endWidth = 256 * display.contentScaleX
local endHeight = 256 * display.contentScaleY
[/lua]
That way the image is always 256px w/h no matter the device.
Hi Jon
What does it mean? If I made the changes you suggested, the picture I got is much smaller, which is not the end size I really want.
…[some research & thinking]…
But I think I got it after a second thought. I think it doesn’t apply to my case because I want the end size to be scaled according to different devices.
Thanks a lot for reminding me of this.
Joe
OK, I’m uploading the image so I want the physical size of the images to be consistent. If you are displaying them, then better skip that modification.
hi, Jon
I saw he also mentioned
Depending on which capture API you are using, you might notice some edge artifacts though (if the final dimensions aren’t a multiple of 4 pixels).
And I do see this kind of artifact edge in some of my rendered images.
Do you know any method to solve this? (If my final dimensions aren’t a multiple of 4 pixels)
Have you tried cropping in a multiple of 4 and then resize to desired size?
I adjusted the final image size to be a multiple of 4, then it’s ok
I thought it’s ok, but after a few days observations, some of the pictures still have artifact edges… although I have adjusted the final size to be a multiple of 4 pixels… 
Thanks a lot, this was really useful for me right now 
I found the artifacts edges might appear/disappear when using different devices
I am using “ZoomEven”
I am wondering if the final size has to be calculated with something else, like the viewable height/width
Try the modification I mention above:
[lua]
local endWidth = 256 * display.contentScaleX
local endHeight = 256 * display.contentScaleY
[/lua]
Then rescale the resulting image.
I made this crop function you could use. In example at bottom I’m using a red rect, just use display.newImage instead of the rect.
[lua]
local function crop(photo, newFileName)
– End size we want
local endWidth = 256
local endHeight = 256
local tempGroup = display.newGroup()
photo.x = display.contentCenterX
photo.y = display.contentCenterY
tempGroup:insert(photo)
– Find the bigger scale out of widht or height so it will fill in the crop
local scale = math.max(endWidth / photo.width, endHeight / photo.height)
photo:scale(scale, scale)
– This object will be used as screen capture boundaries object
local cropArea = display.newRect(display.contentCenterX, display.contentCenterY, endWidth, endHeight)
cropArea.x = display.contentCenterX
cropArea.y = display.contentCenterY
cropArea : setReferencePoint(display.CenterReferencePoint)
cropArea.alpha = 0.0
tempGroup:insert(cropArea)
– Now capture the crop area which the user image will be underneith
local myCaptureImage = display.captureBounds(cropArea.contentBounds)
display.save(myCaptureImage, newFileName)
--myCaptureImage:removeSelf() – Remove captured image
--myCaptureImage = nil
tempGroup:removeSelf()
tempGroup = nil
end
local photo = display.newRect(10,10,100,400)
photo:setFillColor(255,0,0)
– Put cropped photo into documents directory
crop(photo, “cropped.png”)
[/lua]
Joe, as per reply from @mpappas here http://forums.coronalabs.com/topic/38651-change-size-of-displaysave-image/
I think its a good idea to modify line 4 and 5 to:
[lua]
local endWidth = 256 * display.contentScaleX
local endHeight = 256 * display.contentScaleY
[/lua]
That way the image is always 256px w/h no matter the device.
Hi Jon
What does it mean? If I made the changes you suggested, the picture I got is much smaller, which is not the end size I really want.
…[some research & thinking]…
But I think I got it after a second thought. I think it doesn’t apply to my case because I want the end size to be scaled according to different devices.
Thanks a lot for reminding me of this.
Joe
OK, I’m uploading the image so I want the physical size of the images to be consistent. If you are displaying them, then better skip that modification.
hi, Jon
I saw he also mentioned
Depending on which capture API you are using, you might notice some edge artifacts though (if the final dimensions aren’t a multiple of 4 pixels).
And I do see this kind of artifact edge in some of my rendered images.
Do you know any method to solve this? (If my final dimensions aren’t a multiple of 4 pixels)
Have you tried cropping in a multiple of 4 and then resize to desired size?