'16-'17 General Discussion for Lesson 2.3


Use this thread to discuss your questions and comments about how to run the lesson.


My students are able to use the “save image” and paste in the Activity Guide that I download into a word document. They are unable to copy/paste or use the drag feature.

Did anyone else have this problem?



I had that problem as well. If you open it into a new tab, then you can save as a picture and it works. An extra step, but it works OK. Sorry if this is too late to be of help to you.


The Teaching Tips video refers to a walk around card. Is that something that is still available? I am wondering where to find it, if so. Thanks!


I noticed this too. I just had students right click in the image IN the studio.code.org window where they were editing - from there they could “save as” or copy the image.


@jennifer.woughter That’s a great question! I looked through last year’s guide and I didn’t see this in the old lessons either. From the video, it sounds like it is a just a place to write notes about what students are doing in class that you might want to bring up later and follow up questions you can ask them. @brook do you know anything about these “walk around cards”?


Actually @jennifer.woughter - I found it! Actually, Baker found it, but here it is:


Hmmm… it doesn’t look like it posted… here it.


I had fun with this lesson at TeacherCon. A couple take-aways for when I teach it in my classroom:
I am going to move the vocabulary to mid activity - after they have gotten to play with image creation.
I will also have graph paper on hand for students who need to draw the image before they code it.
The video took away some of the exploration. I may move it to after the students have at least explored the pixelation widget.


Love that image and great take aways! That’s what TeacherCon is all about!!


So, maybe this is an esoteric question but it’s driving me a bit nuts…

Thinking about the meta data, shouldn’t the first bit be 0,0 and therefore
0000 1111 x 0000 1111 would represent 16 pixels
and not
0001 0000 x 0001 0000 which, including the 0,0 pixel would be 17 x 17

By this logic then
0000 0000 x 0000 0000 should be 1 x 1 which is tough to get my head around


For the purpose of the widget, we are not considering the meta data for “placement” of the image. We are just looking at the size of the image. Therefore, for an image of 17 x 17 pixels the binary meta data for “size” is 0001 0001 x 0001 0001. For placement, we would require additional meta data for where to image is placed on the screen (i.e. Image - meta data: size, placement, GPS location, etc.,).
I hope this clears things up.


I agree with @terence.stone25 …about the answer…and with @steve1 about the fact it’s hard to wrap your head around because of other ways we talk about binary and the fact we start counting at zero.

So here’s an esoteric response: zero is weird, man. Depending on the context it might describe nothingness, but it also happens to be the first non-negative integer which we use for counting or enumerating elements.

Here’s a completely non-CS analogy: in Europe they often call the first floor of a building, floor 0. But that doesn’t mean there is no floor there! It means they are enumerating floors starting at zero. If that’s the only floor in the building we would say: this building has one floor - floor 0.

Back to CS: the first bit (upper left bit) of the image itself is at coordinate 0,0. But that doesn’t mean there is no pixel there! There is 1 pixel. A 1x1 image has 1 pixel and that pixel is the zeroth pixel in the image.

The meta-data describes the size of the image not the set of values of possible coordinates.

@steve1 your last statement:

By this logic then
0000 0000 x 0000 0000 should be 1 x 1 which is tough to get my head around

Also by this logic we have no way to describe an image with zero pixels. Here’s this for mind blowing: using this protocol it takes 16 bits to say the image has zero pixels.

It could be that someone decided, you know what, we don’t need to have an image file format that lets you create a zero-pixel image (easier to just not have a file at all!), but they didn’t. And this is actually common - the metadata of anything (even say an IP packet) should be able to say: this thing has nothing in it! And it takes some number of (metadata) bits to say that. Mind. blown.

For a hyperbolic example: I just saved a blank MSWord document on my computer and looked at the file size – 21,649 bytes (or 173,192 bits). That’s a lot of bits to say nothing is there.

Does that help?


This makes perfect sense. Thank you for the VERY thorough response. (Aside: this is a really good forum.)

And, my limited mind really wants congruity. I was flummoxed by AppLab’s list variable index started at ‘1’ too. (EDIT: as Baker mentions below, AppLab index starts at zero it’s College Board pseudocode that starts at 1.)

I guess the answer is 1) There must be a way to represent a zero pixel image, 2) it’s a protocol so as long as we all agree then that’s what it is.

Thanks for puzzling it out with me!


For the record: App Lab’s list variable index does start at 0. (Also to be clear, App Lab’s language is javascript - which, like most languages starts indexing at 0).

It’s the college board pseudocode language that starts indexing at 1.



Right! Thank you. That’s an important distinction.

“If some one calls you ‘nerd’, the correct response is ‘thank you’.
Nerds start counting at zero.”