Increasing visibility of a pixel

M
Posted By
Mark24
Nov 23, 2003
Views
1034
Replies
31
Status
Closed
I can decrease visibility of a pixel with Eraser Tool, but can I somehow increase it?

For example – there is only one layer, completely empty (transparent) – I use Brush Tool to draw anything (for example with red color – FF0000) – I use Eraser Tool with opacity=50%, and red pixels become 50% visible, but they have the same color – FF0000
– and now I want to increase visibility of those red pixels

The best solution would be editing alpha channel, but I haven’t found such option.

How to Master Sharpening in Photoshop

Give your photos a professional finish with sharpening in Photoshop. Learn to enhance details, create contrast, and prepare your images for print, web, and social media.

RK
Rob_Keijzer
Nov 23, 2003
Mark,

I gather from your post that you paint (visible), then you erase half of it, and then you want to restore visibility?

Then don’t erase I would say. But I’m probably missing something here. Rob
CW
Colin_Walls
Nov 23, 2003
You can duplicate the layer and then merge it with the copy.
M
Mark24
Nov 23, 2003
I gather from your post that you paint (visible), then you erase half of it, and then you want to restore visibility?

It’s just an example – in general I want to edit visibility of pixels (I can deacrese it with Eraser, but I don’t know how to increase it)

You can duplicate the layer and then merge it with the copy

Yes, it is the way to increase visibility, but it’s not precise at all.
RK
Rob_Keijzer
Nov 23, 2003
Mark,

You can not increase visibility, for the same reason that you can’t fill a bucket that is already full.

When you paint pixels with an opacity of 255 then that is the maximum. you can erase them, but you can’t increase them.

Most things have a limit. Don’t look straight into the sun. Don’t travel faster then light.

Rob
M
Mark24
Nov 23, 2003
You can not increase visibility, for the same reason that you can’t fill a bucket that is already full.

That’s why I gave my example, in which pixels have visibility smaller than 100% Another example is when you draw on an empty layer with Brush Tool and opacity smaller than 100% – that also gives pixels not 100% visible.
Look at this:
<http://g.pl/~cure/stacher/test1.gif>

On the rigt, there are 100% visible, red color pixels (FF0000), in the middle 50% visible pixels (but the color is the same red – FF0000) and on the left 10% visible red pixels.
What I want to do, is make pixels on the left (or those in the middle) more visible (not changing their color)
Are you saying that this couldn’t be done?
CW
Colin_Walls
Nov 23, 2003
You can duplicate the layer and then merge it with the copy

Yes, it is the way to increase visibility, but it’s not precise at all.

Precise? By varying the opacity of the layer(s) before you merge, you can get any opacity you want. If it won’t go high enough, slap on another layer. What am I missing?
M
Mark24
Nov 23, 2003
By varying the opacity of the layer(s) before you merge, you can get any opacity you want

Of course, but it’s not a comfortable way to do it. Imagine you want to increase visibility from 1% to 99%.

It would be perfect, if there was something like "Quick Mask Mode", but for visibility of pixels, not the selection. – You could then change it from 1% to 99% with single use of Brush, you could also make gradients of visibility, etc.
CW
Colin_Walls
Nov 23, 2003
Of course, but it’s not a comfortable way to do it. Imagine you want to increase visibility from 1% to 99%.

Point taken.
CW
Colin_Walls
Nov 23, 2003
Of course, but it’s not a comfortable way to do it. Imagine you want to increase visibility from 1% to 99%.

Actually, I just tried that. It wasn’t really hard.
JS
John_Slate
Nov 24, 2003
layer masks
GA
George_Austin
Nov 24, 2003
Mark,

You have asked a profound quetion. Say that you erase in many different areas with many different brush opacities. Opacity is now an additional pixel attribute besides its RGB attributes. The opacity has become another parameter, not assigned to the entire layer but varying point-to-point. Yet, there is no channel added to bear this opacity data. And there is no new layer. And the file size remains unchanged—It doesn’t appear to have changed by so much as one bit. Where, in the name of Jupiter, is this data? It’s got to be hiding SOMEWHERE.

George
CW
Colin_Walls
Nov 24, 2003
John:

Can you please expand. I can’t see how masks help here.

George:

Very good point. I am intrigued.
PC
Pierre_Courtejoie
Nov 24, 2003
Mark 24, what you ask sounds like a layer mask…

George, opacity of an erased layer is stored in an invisible alpha… to see it, Control+click on the layer, you have now a selection of its opacity. Hit the new alpha channel button, and then fill with white (CTRL+Delete)

To remove the erasing, I JUST FOUND A TECHNIQUE!!!!!

Select the clone stamp tool, set its blending mode to behind, and click the aligned button. Click Alt but don’t move it at all before releasing, so that the cloning area is the same as the source!

You can now paint back the lost opacity… unless it is set at 0
M
Mark24
Nov 24, 2003
what you ask sounds like a layer mask

it may sound so, but it’s something different – you cannot increase visibility of a pixel with a layer mask, you can only decrease it (mask a pixel).

opacity of an erased layer is stored in an invisible alpha

that’s the problem – how to edit this invisible channel

I JUST FOUND A TECHNIQUE!!!!! Select the clone stamp tool…

OK, but it’s just multiplying the opacity, you can’t increase opacity of all pixels by 1%
CW
Colin_Walls
Nov 24, 2003
Isn’t this clone stamp technique doing the same thing as duplicating and merging layers? As I said before, this works fine and it isn’t hard to get from very low to high percentages.
PC
Pierre_Courtejoie
Nov 24, 2003
Colin, yes, but it might be faster on big images to just fix the area you want.

Mark, yes, there is no such thing… as a way to increase the visiblity of a pixel the layermask way… because you can avoid having to resort to the workarounds of this thread: always work on a copy of your layer, take snapshots, do not use the eraser but use a layer mask… and if you’ve just messed with the opacity, go back in the history…

Mark, you can increase opacity of 1% with Colin’s method, but with the copied layer at 1% opacity…
M
Mark24
Nov 24, 2003
I have found the solution for precise control over visibility (opacity/transparency) of pixels.

If you have Layer-1, which has pixels with many different visibility values, which you want to edit, do this:
1. Copy Layer-1 to Layer-2
2. Make all pixels on Layer-2 fully visible (for example by duplicating and merging layers, or Clone Stamp trick described earlier)
3. Load selection from Layer-1 (ctrl+LMB on layer)
4. Add layer mask to Layer-2 with this selection (copied from Layer1-) – now, Layer-2 with enabled mask looks the same as Layer-1 without mask
5. Yoy have full control over transparency by editing mask of Layer-2 with any tool you want. After editing you can apply mask to Layer-2 – this will give image from Layer-1 with changed visibility of pixels.
GA
George_Austin
Nov 24, 2003
"…opacity of an erased layer is stored in an invisible alpha… "

Pierre, if that is true, why isn’t the creation of a new alpha channel confirmed by a file size increase?
JS
John_Slate
Nov 24, 2003
A layer mask is a grayscale, and the opacity of any pixel masked by it relates directly to the value of the mask pixel, with black equalling zero opacity and white equalling full opacity. Editing this mask then edits the opacity of the masked pixel. I see a file size increase here from a layer mask… maybe you are thinking of a vector mask.
CW
Colin_Walls
Nov 24, 2003
John:

I can see that a mask can be used to reduce opacity – do it all the time – but Mark wants to increase opacity.
JS
John_Slate
Nov 24, 2003
painting with white on the mask would do that
GA
George_Austin
Nov 24, 2003
John,

No mask is apparent when you erase yet, if you erase with the eraser opacity less than 100%, that reduced opacity in the erased areas is retained in the file. There is no mask,no layer, no channel for it. Pierre says its hidden. But there is no increase in file size to accomodate the additional data. With 3 bytes used for the tonal data, one additional byte would be needed for opacity so the total number of bytes should increase 33%—unless there is some kind of trade-off in color depth vs opacity.

George
M
Mark24
Nov 24, 2003
George,

The file size does increase, but I’m sure that Photoshop has some kind of compressing/optimizing algorithms, so it’s hard to notice.

Try to do this – open new document 2000×2000 pixels. PS shows on status bar size 11,4M/0K – it means that document after flattening, without transparency has 11,4 MB of uncompressed data (2000*2000*3*8 – 3 channels 8 bits, it is the size of final product – one layer image without transparency). And the second number (0 K) means that there is 0 KB of information in this document. If you now start to draw anything the first number stays the same (because document has the same dimensions, the same RGB mode and the same 8 bit mode), but second number increases. It will also increase if you erase something (especially in "brush" mode with soft brush, because there will be many different values of pixels visibility)
Furthermore, try to add noise on this layer – PS will show 11,4M/11,4 and after that erase something in "brush" mode with soft brush – you can go up to 11,4M/15,2M, which is equal to 2000*2000*4*8, which means that visibility has 8 bits per pixel.
PC
Pierre_Courtejoie
Nov 24, 2003
From Photoshop Channel Chops by Biedny, Moody, and Monroy: "The (new) layer is fully transparent (…) the pixels laid down by the paintbrush are opaque, with soft edges that enable varying amounts of the background to show through (…) In essence, Photoshop is building a mask, on the fly, for the layer; as pixels are added, the transparency msik of the layer is modified. This transparency mask isn’t visible in the way that other Photoshop Masks are-it’s implied…" of course, to see the transparency mask, one has to CTRL+clcik the layer, then create a channel, and fill with white…
GA
George_Austin
Nov 24, 2003
Mark,

Apologies, but I do need to correct your numbers: On the status bar, those are megaBYTES, not megaBITS, so you should not be multiplying by 8.

2000 x 2000 x 3 = 12,000,000 bytes. You must then divide by 1024 x1024 to get 11.44 MegaBYTES, which is the number on the status bar. That is because 1KB is 1024 bytes and 1MB is 1024 KB. Would you believe that 1GB is 1000 MB rather than 1024 MB? And a terrabyte is who knows what? 🙂

George
GA
George_Austin
Nov 24, 2003
Pierre,

That’s making sense to me. So only the opaque pixels count and, since ordinarily most of the pixel sites on the mask are transparent, you don’t add a byte of overhead for every site—just for every OPAQUE site on the mask. The increased byte count would, in general, not be noticed in the status line tally which only shows 3 significant figures. The increase goes undetected unless you do a massive erasure with an eraser opacity less than 100%. Good show. Thanks.

George
JS
John_Slate
Nov 24, 2003
The whole time, I was talking about the other type of layer mask, not the "implied" ones you could see by loading the layer’s transparency as a selection and filling, but the type that you manually add to a layer. I was not suggesting this as a method by which to add back opacity in the exact scenario layed out by the original post, but as a general method of bi-directional editing of pixel opacity (not layer opacity). So you could add a layer filled with red, and add a layer mask, and fill said mask with 50% black and the red would be 1/2 opacity. Then painting black on the mask would bring the red opacity down, and painting white on the mask would bring the red opacity up.
M
Mark24
Nov 25, 2003
George,

Of course, I was counting bits.

Would you believe that 1GB is 1000 MB rather than 1024 MB?

I’m afraid it’s not so simple 😉 Just look here:
< http://www.romulus2.com/articles/guides/misc/bitsbytes.shtml>
GA
George_Austin
Nov 25, 2003
Mabirk,

That reference really puts the matter to bebibed ! Bi the way, I see that I was crossing over from bibinary to debicimal at the gibiga level.

Bi Bi, Gebiorge
DM
dave_milbut
Nov 25, 2003
yea, THAT’LL catch on! 🙂 Thanks for the link though mark! It’ll go over great at the office!
DN
Douglas_Nelson
Nov 26, 2003
Take a snapshot and point the History Brush to that snapshot. Set the brush’s blending mode to Multiply. Paint back in opacity with all the normal brush controls (ie: opacity, pressure, flow, etc.).

http://www.retouchpro.com

How to Improve Photoshop Performance

Learn how to optimize Photoshop for maximum speed, troubleshoot common issues, and keep your projects organized so that you can work faster than ever before!

Related Discussion Topics

Nice and short text about related topics in discussion sections