How to make an image that is transparent in the background?

[Mehdi Ghorbani Saeidian]

Hello friends;

As I have tested before, we can just use images that are bmp type and also they should be 16 and 24 I think. I wanted to make an object that has no background. Let me explain with an example:

I used this article. The problem is when I want to create an image I don't know how to make transparent background. I used black bg and white bg, but none of them worked.
Do you know how I can fix it?

[Krasimir Milchev]

The reason isn't the black vs white background — it's that a 24-bit BMP has no alpha channel at all, so there's nothing to make transparent. Two things usually fix this:

1. If you don't actually need an image file, skip the BMP and draw straight onto a canvas with an alpha-capable format. The default  CreateBitmapLabel  format is  COLOR_FORMAT_XRGB_NOALPHA  (opaque) — that's the usual culprit. Use  ARGB_NORMALIZE  and erase to a fully transparent background:

#include <Canvas\Canvas.mqh>
CCanvas canvas;
canvas.CreateBitmapLabel("myImg", x, y, w, h, COLOR_FORMAT_ARGB_NORMALIZE);
canvas.Erase(0);                                   // 0 = fully transparent
canvas.FillCircle(w/2, h/2, 40, ColorToARGB(clrDodgerBlue, 255));
canvas.Update();

Erase(0) leaves the background see-through and only what you draw (with alpha in the color's A byte) shows up.

2. If you specifically need to load a picture, it has to be a 32-bit BMP with a real alpha channel — and save it in top-down row order. CCanvas has a long-standing quirk where a bottom-up BMP renders only the top half, which sends a lot of people down the wrong path.

ARGB_NORMALIZE premultiplies alpha for you, so blending over the chart looks correct out of the box. Start there.

[Connor Michael Woodson]

Mehdi Ghorbani Saeidian:

Hello friends;

As I have tested before, we can just use images that are bmp type and also they should be 16 and 24 I think. I wanted to make an object that has no background. Let me explain with an example:

I used this article. The problem is when I want to create an image I don't know how to make transparent background. I used black bg and white bg, but none of them worked.
Do you know how I can fix it?

I couldn't get transparency to work with BMP's either. I used the MQL5 PNG library to use PNG's instead.

[Krasimir Milchev]

The catch is the format: a 16- or 24-bit BMP has no alpha channel, so it simply can't carry transparency — there's no "no background" for it to store, which is why nothing you tried worked, whatever colour you used.

You need an image with an alpha channel:

• a PNG — transparency built in, simplest path, and it's what Connor switched to, or
• a 32-bit BMP with an alpha channel — save it top-down, or only the top half shows.

Make it in any editor (Paint.NET, GIMP, Photoshop) with the background erased to transparent, export as PNG or 32-bit BMP, and load that — the bars will sit with the chart showing around them, exactly like your example.

[Connor Michael Woodson]

Krasimir Milchev #:

The catch is the format: a 16- or 24-bit BMP has no alpha channel, so it simply can't carry transparency — there's no "no background" for it to store, which is why nothing you tried worked, whatever colour you used.

You need an image with an alpha channel:

• a PNG — transparency built in, simplest path, and it's what Connor switched to, or
• a 32-bit BMP with an alpha channel — save it top-down, or only the top half shows.

Make it in any editor (Paint.NET, GIMP, Photoshop) with the background erased to transparent, export as PNG or 32-bit BMP, and load that — the bars will sit with the chart showing around them, exactly like your example.

I've tried unsuccessfully with Krita, Photoshop CS6, and MS Paint. MS Paint was an old version, perhaps newer versions will work better. One thing I like about the PNG library is that it has a resize function so I can scale the PNG for high-resolution displays.