AW: How to test if an image is empty?

[Ken Ray]

> Thanks Mark and Scott,
> "the text" ... hmm, not the first to think about with an image :)

If it helps, Tiemo, you can use this:

  put "" into image 1

and 

  if image 1 is empty then...

The "text" property is implied in the same was as for fields ("put field 1 into.." vs. "put the text of field 1 into...").

Here's a good way to think about images: there's a distinction between the actual image binary data and what is used to show the user what the image currently looks like (including scaling, rotation, rendering in various quality levels, the "paintCompression", etc.). The binary data is the image's *contents* (the 'text' of the image in this case), and what is shown to the user is the 'imageData'+'maskData'+'alphaData' (which I'll just call "image data"). If you empty out the image data, the binary data still exists - all you've done is to say (in effect) "don't show this image to the user", or more accurately: "show blank to the user".

You can have binary data without image data but not the other way around; once you set the image data of an image, the binary data is *created* to support the image data you set. This can be very useful in keeping a scaled version of an image in a stack without holding on to all the extra "weight" of the original image. 

So for example, if you imported a 100K image that was 1000 x 1000 pixels and then scaled it down to 100 x 100 (and set the lockLoc to true so it doesn't "pop" back to its original size), the user would see 100 x 100 pixels of image data, but the image would be storing 1000 x 1000 pixels of binary data. However, if you created a new blank 100 x 100 image an then executed:

   set the imageData of img 2 to the imageData of img 1
   set the alphaData of img 2 to the alphaData of img 1
   set the maskData of img 2 to the maskData of img 1

the binary data for img 2 would only be what is necessary to support what the user sees (100 x 100 pixels). It would look exactly like image 1, but would be only 1% of the original number of pixels and would only take up 1K instead of 100K. You could then delete image 1 and you'd have exactly what you started with but storing a bunch less space.

This is great for working with thumbnails of full-resolution images; of course if you *need* to keep the full-res image around because the image might scale *up* from 100x100 to 1000x1000 (or any size in between) then you want to work with the full-res image and not make a "cheap copy", but you get the idea.

I have a very old (but still mostly accurate) primer on imageData, alphaData, and maskData here:

http://www.sonsothunder.com/devres/revolution/tips/imag003.htm

Hope this helps,

Ken Ray
Sons of Thunder Software, Inc.
Email: kray at sonsothunder.com
Web Site: http://www.sonsothunder.com/	



> Thanks for your quick response
> Tiemo
> 
>> -----Ursprüngliche Nachricht-----
>> Von: use-livecode-bounces at lists.runrev.com [mailto:use-livecode-
>> bounces at lists.runrev.com] Im Auftrag von Scott Rossi
>> Gesendet: Montag, 11. Juli 2011 11:48
>> An: LiveCode Mail List
>> Betreff: Re: How to test if an image is empty?
>> 
>> Recently, Tiemo Hollmann TB wrote:
>> 
>>> when I put empty into img "foo" the imagedata of img "foo" is still not
>>> empty, there are still any binary data in the image.
>>> 
>>> I can't test if the imagedata of img "foo" is empty" nor can I test if
> the
>>> img "foo" is empty. How can I test if I have put empty into an image?
> Can I
>>> test it binary?
>> 
>> To "truly" empty an image, I set the text property of the image to empty,
>> and also check that property to make sure it's empty.
>> 
>>  return (the text of img 1 is empty)
>> 
>> Regards,
>> 
>> Scott Rossi
>> Creative Director
>> Tactile Media, UX Design
>> 
>> 
>> 
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